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Home / FHWA Review of ET-Plus / Safety Analysis of Extruding W-Beam Guardrail Terminal Crashes

FHWA Review of ET-Plus

Safety Analysis of
Extruding W-Beam Guardrail
Terminal Crashes

Report from Joint AASHTO-FHWA Task Force on
Guardrail Terminal Crash Analysis


Joint AASHTO-FHWA Task Force Members

Federal Highway Administration (FHWA) representatives

American Association of State Highway Transportation Officials (AASHTO) representatives

State Department of Transportation (DOT) representatives

* Denotes membership on AASHTO's Technical Committee on Roadside Safety (TCRS)


Table of Contents

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  1. Executive Summary
  2. Introduction
  3. Task Force Methodology
  4. Task Force Findings
  5. Conclusions and Recommendations
  6. Appendix A – Glossary
  7. Appendix B – Summary of State Responses
  8. Appendix C – Narrative Summary of 231 Crash Cases from Harman Data Source
  9. Appendix D – Listing of Crash Cases
  10. Appendix E – Examples of Crash Cases Not Forwarded for Review by Task Force

DISCLAIMER

The FHWA and AASHTO thank all sources of the information considered in this report for their voluntary submission of that information with the common goal of ensuring safety of roadside safety hardware. Any opinions, findings, conclusions or recommendations expressed in this publication are those of FHWA and AASHTO and do not necessarily reflect the views of those who provided graphical or photographic submissions cited within. Any personally identifiable information has been removed from all images to maintain the privacy of individuals. The U.S. Government does not endorse products or manufacturers. Trademarks or manufacturers' names may appear on this publication only because they are considered essential to the objective of the report. They are included for informational purposes only and are not intended to reflect a preference, approval, or endorsement of any one product or entity.

EXECUTIVE SUMMARY

This report documents a joint effort between the Federal Highway Administration (FHWA) and the American Association of State Highway and Transportation Officials (AASHTO) to assess the safety performance of extruding w-beam guardrail terminals (also called guardrail end terminals and guardrail end treatments). The Joint Task Force on Guardrail Terminal Crash Analysis (Task Force) was assembled to answer the following questions:

The purpose of this effort was to determine whether there is any evidence of unique performance limitations of the ET-Plus 4-inch guardrail terminal and the degree to which any such performance limitations extend to other extruding w-beam guardrail terminals. This study does not constitute a full in-service evaluation because the available data did not provide a representative sample of terminals in service or a representative sample of terminals that were struck. As a result, the effort does not provide relative comparisons of the in-service safety performance of individual terminal types or an indication of the frequency of occurrence of the individual performance limitations.

The report provides background information on guardrail terminals and covers the data on extruding w-beam guardrail terminals analyzed by the Task Force and independent experts. The data include information received from records and crash reports from States, the public, and interested safety organizations submitted in response to an FHWA Federal Register Notice and Request for Information (79 FR 77595 (Dec. 24, 2014)); from FHWA Division Offices; national databases such as the Fatality Analysis Reporting System (FARS), National Automotive Sampling System Crashworthiness Data System (NASS CDS), the National Motor Vehicle Crash Causation Study (NMVCCS), and the multi-state Highway Safety Information System (HSIS).

The FARS and HSIS analyses provided estimates of the frequency and severity of crashes with guardrails. The FARS analysis indicates that fatal crashes with guardrails involving passenger cars and light trucks represent less than one percent of the almost 33,000 fatalities nationwide that occurred in 2013. In the same year, passenger car and light truck fatalities in which the most harmful event was a collision with a guardrail face or guardrail end (which includes all types of crashworthy guardrail terminals and non-crashworthy terminals such as blunt ends and turn-downs) represent 0.6 percent and 0.2 percent, respectively, of total highway fatalities. The HSIS analysis indicates that the majority of crashes when guardrails were coded as the most harmful event resulted in property damage only (75 percent for guardrail face and 61 percent for guardrail end).

The combined number of crashes FHWA received through its external outreach and that it could glean from the crash records contained in national databases for guardrail terminals was 1231 (the complete list of the crashes received is contained in Appendix D). FHWA conducted an initial screening of these cases to determine whether they contained sufficient detail to evaluate:

The cases received varied considerably in the level of detail each contained. FHWA was able to review several data sources that became available before the Task Force was formed, and through the initial screening, was able to keep the effort on schedule. FHWA shared with the Task Force the methodology used to screen the cases and forwarded to the Task Force those cases that provided sufficient information to allow them to evaluate the role the terminal played in the crash. These cases concentrated on crashes involving severe or fatal injuries, occupant compartment penetration or deformation, rollover, or where the outcome appeared to be unusual or extreme. Out of the 1231 cases, 161 cases were selected for the Task Force's detailed review and analysis. These cases that comprised the focus of the review were viewed as the most likely to show potential performance limitations and represented a limited sample across five different guardrail terminals. The data in this assessment were skewed toward severe crashes involving ET terminals; a limited sample of SKT and FLEAT cases were captured.

The information provided for the 1231 crash cases was inconsistent and prevented an in-depth analysis of each crash. For some cases, there was enough information to allow a reasonably informed evaluation of the performance of the terminal. However, the conclusions should not be interpreted as definitive. The limitations highlight the need for well-designed in-service performance evaluations of all guardrail terminals with a comprehensive sample representing all crash severities (fatal, serious injury, moderate injury, minor injury, and property damage only crashes). Nevertheless, from this analysis of the 161 crashes which were predominantly ET-Plus 4-inch devices (ET 2000, ET-Plus 5-inch, SKT, and FLEAT devices also were included), some performance limitations could be gleaned in two broad areas for extruding w-beam guardrail terminals: impact conditions and installation conditions. The evidence did not suggest that these performance limitations are limited to the ET-Plus 4-inch device.

Based on the analysis, the Task Force developed the following conclusions and recommendations to address the identified w-beam guardrail terminal performance limitations.

Conclusions

  1. Guardrail Terminal Crash Test Impact Conditions and Field-installed Conditions - The review of guardrail terminal performance based upon the limited number of crashes confirms what is acknowledged in National Cooperative Highway Research Program (NCHRP) Report 350[1] and the AASHTO Manual for Assessing Safety Hardware (MASH)[2] – there are real-world impact conditions that vary widely from the crash test matrices as related to vehicle type and sizes, first point of vehicle impact, vehicle non-tracking, and vehicle speed. Also, there are different installation and maintenance practices in place that can affect safety performance. Within the roadside safety community, it is recognized that even with the "best" practice of terminal design, with the wide variety of traffic and field conditions and applications, there will be crashes that exceed the performance expectations for the terminals. In addition, roadside features such as ditches, curbing, uneven terrain, and steep slopes in the vicinity of the terminal factor into the ability to mitigate the severity of the outcome of a guardrail terminal crash event. These terrain features can contribute to an increased likelihood of rollover during or after the impact event.

  2. Performance Limitations – Performance limitations are factors in a real-world crash environment that can contribute to the unsuccessful performance of a roadside safety hardware device. As indicated in MASH, guardrail terminals "are generally developed and tested for selected idealized situations that are intended to encompass a large majority, but not all, of the possible in-service collisions." Satisfactory performance can typically be expected for collision conditions similar to the test conditions. However, the performance of these devices is dictated by physical laws, vehicle stability, vehicle crashworthiness, and the site conditions of these real-world crashes. The more the crash conditions differ from the test conditions, the more likely it becomes that performance will be outside of the desirable limits.

    Through its analysis, the Task Force identified several performance limitations for all types of extruding w-beam guardrail terminals reviewed in this study. The limitations fall into two general categories: 1) impact conditions, and 2) installation conditions. For impact conditions, the primary performance limitations that were identified include: 1) side impacts, 2) head-on/shallow-angle corner impacts, and 3) head-on/shallow-angle high-energy impacts. For installation conditions, the performance limitations identified include: 1) hardware installation/maintenance/repair issues, 2) grading issues, and 3) placement that does not conform to accepted guidance and practice. These installation conditions can adversely affect the safety performance of these devices, but it is unknown to what extent, since terminals are crash tested under ideal, controlled conditions.

  3. NCHRP Report 350 Crash Test Criteria – NCHRP Report 350 crash test matrices do not specifically address the performance limitations the Task Force identified. It appears that side impacts, head-on/shallow-angle high-energy impacts, and head-on/shallow-angle corner impacts may lead to safety performance issues. However, the data analyzed did not allow for an assessment of how frequently these situations occur (i.e., they may be limited or they may appear on a regular basis) in the field. The shallow angle impact test condition is addressed in the MASH crash test criteria, but side impacts and front corner impacts are not specifically addressed in MASH. This points to the need to conduct in-service performance evaluations on roadside safety hardware including guardrail terminals; these evaluations are critical to determine whether crash-tested hardware have performance limitations that are not detected by the testing process and should be used to amend the crash test criteria in subsequent updates.

  4. Crash Testing of Extruding W-beam Guardrail Terminals – The Task Force considered additional crash testing of all existing NCHRP 350-compliant extruding w-beam guardrail terminals but concluded that such testing would not be informative because the performance limitations identified for these terminals fall outside of the NCHRP 350 testing matrices.

Recommendations

The Task Force developed the following recommendations:

  1. Fully Implement MASH Compliance for New Installations of Guardrail Terminals – This action is related to the roadside safety community setting a date by which new installations of guardrail terminals should be consistent with the MASH crash test criteria. MASH testing incorporates changes in the crash matrix details that will be more discerning for guardrail terminals. More specifically, MASH addresses impacts that occur at shallow angles, which is an important element in two of the performance limitations identified in this report. Each successive version of crash testing guidelines is meant to encourage manufacturers to advance the state of the practice and to develop safety devices that work with a changing vehicle fleet under a wider range of conditions. Because of the extensive development and testing required, it typically takes many years after roadside safety hardware guidelines are established for products meeting those guidelines to be widely available on the market. However, in the six years since MASH was published, there have not been a significant number of MASH-tested devices developed and brought to market. Therefore, in order to encourage the expanded development and installation of MASH-compliant devices, the Task Force supports the roadside safety design community to expeditiously transition to the MASH criteria for all new installations of guardrail terminals.

  2. Conduct In-Service Performance Evaluations of Guardrail Terminals – The Task Force recommends that comprehensive in-service performance evaluations of guardrail terminals be conducted at the national and State levels. As previously highlighted in this report, the Task Force's assessment did not involve a complete in-service evaluation and concentrated on a limited group of mostly higher severity crashes, specifically focused on crashes with the ET-Plus terminal. The findings of this report should be considered by the National Academies' National Research Council (NRC) committee that is conducting a project entitled "In-Service Performance of Energy-Absorbing W-beam Guardrail End Treatments." The intent of the NRC committee is to conduct exploratory work to determine what data are available, in sufficient quantity and quality, to allow for meaningful in-service evaluation studies of guardrail terminals.

  3. Expand Documentation of Guardrail Crashes – The Task Force recommends that AASHTO and FHWA encourage public agencies to thoroughly document guardrail crashes in order to allow for conducting more comprehensive in-service evaluations. Photographic evidence of an impacted guardrail and damaged vehicle(s) involved in a crash is extremely valuable and not typically captured. In addition, the Task Force recommends that AASHTO and FHWA request that the National Highway Traffic Safety Administration (NHTSA) thoroughly document guardrail crashes in its Crash Investigation Sampling System which is being phased in over the next two years as the replacement for the NASS CDS. Also, NCHRP project 17-43, "Long-Term Roadside Crash Data Collection Program," is providing an opportunity to improve data pertaining to roadside safety hardware that helps address this recommendation.

  4. Advance Noteworthy Safety Data and Roadside Hardware Inventory Practices – The Task Force recommends that the highway safety community and transportation agencies bring forward noteworthy practices for developing and maintaining roadside hardware inventory systems and also those that link crash data to the location and type of roadside safety devices. This linking is important and critical to obtain complete information for analyzing roadside crashes. FHWA has a noteworthy practices database established at the following web location where this information could be added in the future: (http://rspcb.safety.fhwa.dot.gov/noteworthy/default.aspx).

  5. Conduct Research on Vehicle Corner Impacts with Guardrail Terminals – The Task Force recommends that AASHTO and FHWA conduct research to evaluate the performance of vehicle front corner impacts with guardrail terminals to gain a better understanding of these crashes and the circumstances and conditions associated with them. Greater knowledge of this crash type could potentially be used to update future crash testing criteria. As summarized by this report, there were observed performance limitations with extruding w-beam guardrail terminals when the impact occurred at or near the vehicle corner in the headlight area.

  6. Conduct Research on Vehicle Side Impacts with Guardrail Terminals - The Task Force recommends that AASHTO and FHWA conduct research to evaluate the performance of vehicle side impacts with guardrail terminals to gain a better understanding of these crashes and the circumstances and conditions associated with them. Greater knowledge of this crash type could potentially be used to update future crash testing criteria. As summarized by this report, there were observed performance limitations with extruding w-beam guardrail terminals when the impact occurred on the side of the vehicle. The opportunity for research should be explored with NHTSA to review vehicle standards relative to the strength of the sides of passenger vehicles and to determine if vehicle side impacts into terminals and other fixed objects can be better addressed.

  7. Promote Proper Placement, Installation, and Maintenance Practices – The Task Force recommends that appropriate placement, installation, and maintenance practices be shared with the roadside safety community as was recently done through FHWA's May 26, 2015 memorandum. FHWA provides training and technical assistance on these practices, and the Task Force recommends that highway agencies take advantage of these resources. In addition, the Task Force recommends that AASHTO, through its Technical Committee on Roadside Safety, include additional content regarding proper placement, installation, and maintenance of guardrail terminals in the next edition of AASHTO's Roadside Design Guide.

  8. Crash Testing of Extruding W-beam Guardrail Terminals – The Task Force does not recommend additional crash testing of existing NCHRP 350-compliant extruding w-beam guardrail terminals for two reasons. First, the performance limitations identified for these terminals fall outside of the NCHRP 350 testing matrices, nor is it expected that NCHRP 350 tested devices function under all real-world conditions beyond what is present in the crash test scenarios. Second, as discussed in recommendation #1, the Task Force recommends that the roadside design community move to full implementation of MASH for all new installations of guardrail terminals which will help address an element of some of these performance limitations. Therefore, additional NCHRP 350 crash testing of existing guardrail terminals would be irrelevant since all crash testing since January 2011 has been required under the MASH criteria.

INTRODUCTION

Purpose

This report documents a joint effort between the Federal Highway Administration (FHWA) and the American Association of State Highway and Transportation Officials (AASHTO) to assess the safety performance of extruding w-beam guardrail terminals. The Joint Task Force on Guardrail Terminal Crash Analysis (Task Force) was assembled to answer the following questions:

To address the first question, a broad array of data from different sources was assembled and analyzed. This effort began when FHWA asked AASHTO to include questions regarding the performance of w-beam terminals in a 2012 survey of its Standing Committees on Highways' Subcommittees on Maintenance and Design. The effort expanded to include:

This report provides a background and some history of roadside safety hardware to set the context and covers the data the Task Force and a group of independent experts analyzed. While a considerable number of crashes involving guardrail terminals were reviewed, the lack of well-documented, detailed records of the crashes limited the breadth and depth of the review. The findings of the analyses of individual crash cases highlight observed performance limitations of extruding w-beam guardrail terminals. The report concludes with a set of recommendations and next steps to help address these performance limitations.

This effort does not constitute a full in-service evaluation because the available data was not a representative sample of terminals in service or a representative sample of terminals that were struck. As a result, the effort does not provide relative comparisons of the in-service safety performance of individual terminal types or an indication of the frequency of occurrence of the individual performance limitations. This type of comparison requires a well-designed and executed research study to collect all of the necessary data and account for exposure and confounding factors such as proper installation. Clearly, for this effort, a comparison was not possible given the limited available data and because the focus of the data reviewed was mostly on crash cases involving atypical or extreme conditions.

Guardrail Terminal Background

Guardrail design has evolved and improved significantly to reduce the risk of injury or death when a vehicle leaves the roadway. Since the mid-1960s, improvements have been guided both by observation of the performance of existing systems and by increasingly stringent testing of proposed systems.

However, a guardrail is intrinsically a roadside object that may be struck by an errant vehicle, albeit a roadside object that is intended to reduce crash severity by shielding a motorist from a hazard. A guardrail system should only be installed when the risk of impacting it is lower than the risk associated with encountering the objects shielded by the guardrail system.[3]

Guardrail systems are generally designed to accommodate the most common vehicles (i.e., passenger cars, pickup trucks, vans, and sport-utility vehicles) on a roadway and the "worst practical conditions."

When a crash occurs, there are many variables that may affect the outcome, including the impact speed; pavement condition; amount of braking; the angle of departure from the road; and the rate, direction, or amount of vehicle spin. Crash testing cannot replicate every possible scenario, so representative tests are conducted. For example, the AASHTO Manual for Assessing Safety Hardware (MASH) prescribes that crash tests into longitudinal barriers occur at an impact speed of 100 km/h (62 mph) and an impact angle of 25 degrees to represent the "practical worst case" for passenger vehicle impacts into guardrail systems installed on most high-speed highways.

Modern guardrails are intended to reduce the severity of crashes as compared to the trees, utility poles, steep slopes, and other objects they shield. Their primary function is to redirect an impacting vehicle back toward the road. For decades, a major challenge has been to design the terminals of the guardrail to minimize the severity of crashes into the end of a length of a guardrail.

Prior to the 1950s, many terminals consisted of a bent shape of sheet metal that covered the end of the rail, often called a "blunt end." These terminals frequently speared vehicles that ran into them. Moreover, these ends provided little anchorage for the ends of the rail; thus while vehicles impacting the guardrail more than about 30 feet from either end could be safely redirected, a vehicle impacting near the unanchored end of the rail could break through and continue on to the roadside objects it was intended to shield.

The potential risk presented by blunt terminals led to the development of "ramped" or "turned-down" terminals. The concept of these terminals was to secure the leading end down onto the ground where it would not spear into a vehicle. This strategy not only anchored the rail securely, but it essentially eliminated the chance of spearing crashes. It became apparent, however, that this improvement also increased the likelihood of rollover crashes. Rollovers have relatively high injury risks. Even at low speeds, they increase the chance of unbelted motorists being completely or partially ejected and crushed by the vehicle.

The first terminal designed to anchor the guardrail as well as reduce the potential for rollover and spearing was the Breakaway Cable Terminal (BCT). A steel cable connecting the bottom of the first post to the guardrail beam provided an anchor to the barrier. The use of breakaway posts and layout of the terminal on a parabolic flare was designed to allow an errant vehicle to break through the end of the BCT without spearing or rolling over. While this terminal worked effectively for large passenger cars when crash-tested in the early 1970s, later testing with sub-compact cars showed a propensity for spearing.

The roadside design community looked for innovative ways to improve terminal designs. The goal was to develop terminals "soft" enough that the resulting vehicle decelerations were within specified limits for small vehicles, yet "firm" enough to stop larger vehicles. The intended function of the new terminals was to dissipate much of the kinetic energy from the vehicle – which is a function of its mass and speed – by using it to bend, kink, crush, or otherwise deform the elements of the w-beam guardrail. Terminals of this generation are called "energy-absorbing" terminals.

The first energy-absorbing product to reach the market was the Guardrail Extruder Terminal (GET), later named the ET-2000. Together with its successor, the ET-Plus, the Extruder Terminal family comprises the most common energy-absorbing guardrail terminals installed along the Nation's highways. Other extruding, energy-absorbing terminals include the Sequential Kinking Terminal (SKT) and the Flared Energy Absorbing Terminal (FLEAT). Extruding-type terminals are designed to function as follows, depending on the type of impact. During head-on impacts, the vehicle engages the impact head and pushes it down the rail. As the head travels down the rail, it bends and/or flattens the rail and extrudes the rail out the side of the head, essentially moving the rail away from the vehicle. This process dissipates energy from the impacting vehicle. During angled impacts at the end of the terminal, the rail bends away and allows the vehicle to pass through the system. This behavior is called gating, and it typically dissipates much less energy from the impacting vehicle.

National Statistics

This section highlights some key national statistics to quantify the magnitude and severity of crashes involving guardrail and guardrail terminals.

Fatality Analysis Reporting System (FARS)

FARS is a nationwide census providing annual data regarding fatal injuries suffered in motor vehicle traffic crashes.[4] To assess the national role of guardrail terminals, fatality statistics from FARS involving passenger cars and light trucks were assembled, since these are the vehicle types in the recommended tests for safety performance evaluation of terminals.[5] In FARS, the category "passenger cars and light trucks" includes pickup trucks, sport utility vehicles, and minivans.

Furthermore, the FARS analysis considered fatalities in which either the most harmful event or the first harmful event, as defined in FARS, was collision with a guardrail face or guardrail end.[6] FARS defines most harmful event as "the event that resulted in the most severe injury or, if no injury, the greatest property damage involving this motor vehicle." FARS defines first harmful event as "the first injury or damage-producing event that characterizes the crash type." The following examples illustrate the difference between the most harmful event and first harmful event.

The first example involves a single-vehicle crash in which a vehicle departs the roadway, hits the end of the guardrail at an angle causing property damage only, and then goes behind the guardrail end as it "gates" and runs down an embankment, causing the vehicle to roll over with the driver sustaining major injuries. The first harmful event in this example is the guardrail impact, while the most harmful event is the rollover event that resulted in the driver being injured.

The second example involves a multi-vehicle crash in which vehicle A sideswipes vehicle B causing property damage to both vehicles. The driver of vehicle B then loses control and crashes into a guardrail causing an unbelted passenger in vehicle B to be ejected and fatally injured. The driver of vehicle A comes to a stop on the shoulder and sustains no injuries. The first harmful event in this example is the collision of the two vehicles, while the most harmful event is vehicle B impacting the guardrail.

Figure 1 shows the trend from 1979 to 2013 in the annual number of fatalities (on the vertical axis) involving passenger cars and light trucks in which the most harmful event was collision with a guardrail—a decline of 53 percent from 548 fatalities in 1979 to 258 fatalities in 2013. Overall, the total number of motor vehicle fatalities declined 36 percent during the same period.

Figure 1 - Collision with Guardrails as Most Harmful Event in Fatalities involving Passenger Cars and Light Trucks

Figure 1 shows the trend from 1979 to 2013 in the annual number of fatalities (on the vertical axis) involving passenger cars and light trucks in which the most harmful event was collision with a guardrail–a decline of 53 percent from 548 fatalities in 1979 to 258 fatalities in 2013.

Source: Fatality Analysis Reporting System

In 2004, FARS began distinguishing between crashes into a guardrail face (i.e., along the length of the guardrail) and crashes into a guardrail end. Comparing passenger car and light truck statistics from recent years (2005- 2008 time period to 2009- 2013 time period), fatalities from crashes into a guardrail face as the most harmful event declined 15 percent, and fatalities from crashes into a guardrail end as the most harmful event declined 12 percent.

As shown in Table 1, during the past 5 years for which data are available (2009-2013), an annual average of 194 fatalities and 63 fatalities involved passenger cars and light trucks colliding with a guardrail face and end as the most harmful event, respectively.

Table 1 - Number of Fatalities in which the Most Harmful Event Involved Passenger Cars and Light Trucks Colliding with Guardrail Face and Guardrail End: 2009-2013

Most Harmful Event 2009 2010 2011 2012 2013 Average
Collision with Guardrail Face 204 207 178 195 187 194
Collision with Guardrail End 50 54 73 69 71 63

Source: Fatality Analysis Reporting System

In 2013, a total of 32,719 fatalities occurred on the Nation's roads for all vehicle types. Fatalities involving passenger cars and light trucks striking a guardrail face and a guardrail end as the most harmful event represent 0.6 percent and 0.2 percent, respectively, of total highway fatalities in 2013.

Table 2 summarizes the number of fatalities involving passenger cars and light trucks during the most recent five-year period for which data are available in which the first harmful event was collision with a guardrail face or guardrail end. On average, from 2009 to 2013, there were 479 fatalities and 132 fatalities per year in which the first harmful event involved guardrail face and guardrail end, respectively.

Table 2 - Number of Fatalities in which the First Harmful Event Involved Passenger Cars and Light Trucks Colliding with Guardrail Face and Guardrail End: 2009-2013

First Harmful Event 2009 2010 2011 2012 2013 Average
Collision with Guardrail Face 508 524 462 460 439 479
Collision with Guardrail End 125 130 136 126 141 132

Source: Fatality Analysis Reporting System

Fatalities in which the first harmful event was collision with a guardrail face or guardrail end represent 1.5 percent and 0.4 percent, respectively, of total highway fatalities in 2013.

Table 3 shows the number of fatalities with most harmful event for passenger cars and light trucks involving collisions with other fixed objects and obstacles (i.e., trees, utility poles, culverts, sign supports) and rollovers off the roadway.

Table 3 - Number of Fatalities with Most Harmful Event for Passenger Cars and Light Trucks: 2009-2013

Most Harmful Event 2009 2010 2011 2012 2013 Average
Collision with Other Fixed Objects 5,926 5,516 5,365 5,636 5,494 5,587
Rollover Off Roadway 4,780 4,566 4,338 4,380 3,921 4,397

Source: Fatality Analysis Reporting System

The number of fatalities with fixed objects and rollover off roadway as the most harmful event is considerably larger than the number of fatalities with guardrail face and end as the most harmful event. Guardrail systems are put in place to help shield motorists from encountering these objects and for other reasons.

Highway Safety Information System (HSIS)

HSIS[7] is a multi-state database that contains crash, roadway inventory, and traffic volume data for a group of seven States. North Carolina is the only State in HSIS that has data for guardrail face and end. The North Carolina data are presented in Tables 4 and 5. The tables include single-vehicle and multi-vehicle crashes involving passenger vehicles (passenger cars and light trucks). For the multi-vehicle crashes, the analysis captures the most severe injury that occurred in the vehicle for which the most harmful event was a collision with a guardrail face or guardrail end. The multi-vehicle cases in which the most severe injury may have occurred in the vehicle for which the most harmful event was not striking the guardrail have been removed. The KABCO scale is used to characterize injury severity.[8]

In summary, during the past 14 years for which data are available (2000-2013), 0.6 percent of guardrail face crashes and 2.3 percent of guardrail end crashes in North Carolina resulted in a fatality or serious injury. The majority of crashes with guardrail faces and ends as the most harmful event resulted in property-damage only.

Table 4 - North Carolina Single- and Multi-Vehicle (Passenger Vehicle) Crashes Involving Collision with Guardrail Face as Most Harmful Event: 2000-2013

Injury Severity Total Number
(2000-2013)
Average Number per Year Percentage
K 66 4.7 0.2%
A 149 10.6 0.4%
B 2,109 151 5.9%
C 6,499 464 18.3%
O 26,734 1,910 75.2%
Total 35,557 2540 100.0%

Table 5 - North Carolina Single- and Multi-Vehicle (Passenger Vehicle) Crashes Involving Collision with Guardrail End as Most Harmful Event: 2000-2013

Injury Severity Total Number
(2000-2013)
Average Number per Year Percentage
K 36 2.6 0.6%
A 96 6.9 1.7%
B 730 52 13.0%
C 1,341 96 23.9%
O 3,412 244 60.8%
Total 5,615 401 100.0%

General Data on Guardrail Terminals Supplied by States

On October 10, 2014, FHWA made a request through its Division Offices for information from State DOTs regarding the performance of the ET-Plus device in the field. All 50 States responded with varying levels of information. Some States provided general information, some provided crash statistics, and others discussed individual crashes. Appendix A contains an overview of the information each State provided.

This section focuses on the information from a small group of States (Connecticut, Illinois, Iowa, Massachusetts, Missouri, New Hampshire, North Carolina, and Pennsylvania) that provided crash statistics or information on individual crashes. The information is summarized below as reported by these States.

Connecticut

Connecticut indicated it has approximately 213 ET-Plus units (no distinction was made between the 4-inch and 5-inch versions) in the State with approximately 20 impacts on these units. Of these impacts, Connecticut indicated "all units performed well except in one crash where the unit was destroyed with components sticking up vertically after crash. It is unknown if any injuries were sustained in this crash as the vehicle fled the scene."

Illinois

Table 6 summarizes the total number of crashes for all contracts (i.e., projects) in Illinois between 2006 and 2012 as well as the weighted loss per crash (with weights of 25 for a K/fatal crash, 10 for an A severity-type crash, and 1 for a B-type crash on the KABCO scale) and the corresponding severities for the terminal types identified in those contracts.

Table 6 - Illinois Guardrail Terminal Crashes: 2006-2012

Terminal Type # of Crashes Weighted Loss Per Crash Severities
Contract Data (2006-2012)
Total All Types
48    
Crashworthy Terminals 17 0.24 0K, 0A, 4B, 0C, 13 PDO
ET Plus 12 0.25 0K, 0A, 3B, 0C, 9PDO
ET 2000 5 0.20 0K, 0A, 1B, 0C, 4 PDO
       
Non-Crashworthy 31 0.81 0K, 2A, 5B, 0C, 24 PDO

The weighted loss reported per crash was slightly higher for ET-Plus (no distinction was made between the 4-inch and 5-inch versions) relative to ET 2000. The crashworthy terminals had a lower loss per crash than the non-crashworthy terminals. It is important to note that these crash numbers are small making it challenging to draw statistical conclusions from this data.

In Illinois, the 3-year rolling average, for 2004-2013 data, showed a 23% decline in K&A injuries related to terminals (from 8.5% in 2004 to 6.5% in 2013).

The Illinois DOT monitors damage to terminals and replaces or repairs as necessary. It has had no indication from its district offices, local agencies, or the Illinois State Police of any adverse performance issues to date associated with the ET-Plus terminal.

The Illinois Tollway also responded and indicated it has experienced no adverse performance issues with ET-Plus terminals.

Indiana

The Indiana DOT reviewed terminal crashes that occurred in Indiana from January 1, 2007 through October 21, 2014. Its assessment primarily focused on nine crashes: six of the crashes involved the ET-Plus (4-inch or 5-inch channel), and three crashes involved the SKT-350. In eight of the cases, the State found no apparent evidence that any part of the barrier penetrated the vehicle. In the ninth case, which involved the SKT-350 terminal, the officer's report stated that the guardrail penetrated the vehicle and struck the driver. The precise element on the barrier run that penetrated the vehicle and the specific manner in which it did so were not specified. Indiana's investigation discovered no "undesirable pattern of behavior" of the ET-Plus in either the 4-inch or 5-inch channel design.

Iowa

From January 2010 to September 2014 in Iowa, 3 of 7 fatal crashes and 15 of 26 major injury crashes with guardrails involved a terminal. Out of the 18 fatal and major injury crashes into terminals, none involved an ET-Plus. During the same time period, Iowa did have six low-severity reported crashes (two non-incapacitating injury crashes, two possible injury crashes, and two crashes without injury) and four unreported crashes involving the ET-Plus. At the statewide level, Iowa estimates that 30 to 40 percent of all guardrail crashes go unreported.

Massachusetts

During the Massachusetts DOT's initial review of some of its most recent crash data, it found four crashes that appeared to involve vehicle impacts with an ET-Plus terminal.

Of the four crashes, the Massachusetts DOT's initial evaluation was that in two of the crashes, it appeared that the ET-Plus terminal performed as designed. One crash resulted in a fatality but the Massachusetts DOT did not believe that the fatality was related to the performance of the ET-Plus terminal, as the terminal appeared to perform as designed but the vehicle rolled over after impact and the occupant was ejected. In the fourth crash, the Massachusetts DOT indicated it appeared that the impacting vehicle did experience some spearing of the vehicle after impact with an ET-Plus, but no injuries to the occupant resulted from the spearing.

In a submission to the Federal Register Notice and Request for Information, FHWA also received a report from Massachusetts involving an ET-Plus that was damaged and was unrepaired before a subsequent fatal crash.

Missouri

The Missouri DOT provided results from a study it commissioned from the University of Alabama-Birmingham (UAB), as documented in a report entitled In-Service Evaluation of FHWA-Accepted Guardrail Terminals. Following Missouri's submission, UAB revised the report content and changed the title to Relative Comparison of NCHRP 350 Accepted Guardrail Terminals. The study was not able to separate the 5-inch ET-Plus units from the 4-inch units based on the Missouri data. The data from the revised UAB study is presented below.

The study used a sample of approximately 1,550 miles of roadway along which there were 2,399 terminals. The most common type of end treatment was the ET-Plus. The entire distribution of observed systems is shown in Table 7 (displayed as Table 5 in the revised UAB study).

Table 7 - Exposure Data for Guardrail End Crash Locations
(as titled in the original UAB study)

System Total Distribution
ET-2000 961 40.1%
ET-Plus 1,200 50.0%
FLEAT 9 0.4%
SKT 38 1.6%
SRT 191 8.0%
Total 2,399 100.0%

Table 8 (displayed as Table 6 in the revised UAB study) shows A+K and K crashes separately for the different systems.

Table 8 - Simple Probability and Odds Ratios (as titled in the original UAB study)

A+K Crashes
System Accidents Exposure Probability Odds Ratio
ET-2000 49 961 0.0510 1.00
ET-PLUS 93 1,200 0.0775 1.52
FLEAT 0 9 0.0000 0.00
SKT 0 38 0.0000 0.00
SRT 14 191 0.0733 1.44

K Crashes
System Accidents Exposure Probability Odds Ratio
ET-2000 4 961 0.0042 1.00
ET-PLUS 17 1,200 0.0142 3.40
FLEAT 0 9 0.0000 0.00
SKT 0 38 0.0000 0.00
SRT 2 191 0.0105 2.52

The probability of a guardrail terminal being involved in a crash was calculated using the crash site and exposure data for each of the five crashworthy guardrail terminals. In this study, it was assumed that the occupants of the vehicle would have driven 10 miles on the highway prior to a where a crash occurred. Exposure was defined as the number and distribution of end treatments observed in those 10 miles. Using the ET-2000 as a baseline, an odds ratio was calculated relative to the other systems (i.e., the odds of a terminal being involved versus an ET-2000). The odds ratios of the ET-Plus were found to be 1.52 and 3.40 for A+K and K crashes, respectively, when compared to its predecessor, the ET-2000. The study concluded that the ET-Plus is 1.52 times more likely to be involved in a severe injury than the ET-2000, and the ET-Plus is 3.40 times more likely to be involved in a fatal crash than the ET-2000.

This study was independently reviewed by three experts, and the results of the review can be found at https://www.fhwa.dot.gov/guardrailsafety/peerreview.cfm. The reviewers raised concerns about limitations or flaws in the study's methodology, which led all of them to question the validity of the study's findings and conclusions. The Safety Institute provided a response to FHWA's review which can be found at http://www.thesafetyinstitute.org/the-safety-institute-responds-to-critical-fhwa-review-3/, and Dr. Kevin Schrum's response to the review can be found at http://www.regulations.gov/, Docket Number FHWA-2014-0039, under Kevin Schrum - Comments.

New Hampshire

New Hampshire crash reports do not distinguish which section of a guardrail unit is impacted (i.e., longitudinal section or terminal unit). However, the New Hampshire DOT reported that it is aware of a crash on I-93 in the town of Ashland that impacted a recently installed ET-Plus terminal. Based upon a District office's photos of the post-crash event, the State believes the terminal "coiled" as designed with the impacting vehicle coming into contact with the stiffer longitudinal beam guardrail section where the rail eventually kinked. According to news reports, the rail entered the vehicle and seriously injured the two occupants.

Pennsylvania

Based on available data and a high-level data search of the 1,593 suspected crashes within 1000 feet of ET-2000 and ET-Plus known locations, Pennsylvania found only one case in which the guardrail terminal hit was listed as the only harmful event and involved compartment intrusion from the guardrail. Overall analysis of Pennsylvania's 4,936 guardrail terminal crashes between 2009 and 2013 show that 1.4 percent of such crashes resulted in a fatality. The fatality rate in the State for Trinity extruder terminals (ET-2000, ET-Plus 5-inch, and ET-Plus 4-inch) also was 1.4 percent.

TASK FORCE METHODOLOGY

Overview of Data Sources Used to Assess Crash Cases

FHWA conducted a broad search for data on crashes involving extruding w-beam guardrail terminals with the focus on the ET-Plus 4-inch device. This search included an October 10, 2014 e-mail request to FHWA Division Offices in each State, a December 24, 2014 Federal Register Notice and Request for Information, queries of three national databases, multi-state HSIS, inquiries to industry representatives and safety organizations, and media reports.

In total, FHWA received 1231 cases. FHWA conducted an initial screening of these cases to determine whether they contained sufficient detail to evaluate:

Based upon this initial screening, 161 cases were selected for detailed review and analysis. The Task Force was not fully assembled at the time initial screening of certain data sources occurred but was informed regarding the approach taken in identifying the cases for further review. Table 9 summarizes the number of cases initially screened and subsequently reviewed in detail by data source and terminal type. There were some duplicate cases identified across the data sources; for these cases, the one with the most robust data was used for analysis purposes.

Table 9 - Crash Cases Reviewed by Data Source and Terminal Type

Review
Phase
Data Source # of Cases
Screened
by FHWA
# of Cases Reviewed by Task Force by Terminal Type
Total ET-Plus
4"
ET-Plus
5"
ET-Plus
(unknown
channel width)
ET-2000 SKT FLEAT Unknown
or N/A
1A NMVCCS 78 14 0 2 8 4 (2)** (1) ** 0
2A Harman 231 14 13 0 1 0 0 0 0
2B Missouri DOT,
First Submission
34 11 7 0 4 0 0 0 0
3A NASS CDS 56 10 3 3 4 0 0 (1) ** 0
3B Missouri DOT,
Second Submission
38 32 24 1 4 3 (1)** 0 0
4A Delaware DOT 12 8 8 0 0 0 0 0 0
4B Connecticut DOT 6 6 2 0 1 0 0 0 3
4C Washington State DOT 162 20 6* 0 13 1 (5)** 0 0
4D Massachusetts DOT 560 20 0 0 15 0 0 0 5
5A The Safety Institute 39 10 4 2 2 0 0 0 2
5B Media and
Other Sources
15 4 4 0 0 0 (1) ** (1) ** 0
6A Cases involving
SKT and FLEAT
Terminals from
1A, 3A, 3B, 4C
--*** 12 0 0 0 0 9 3 0
TOTAL 1231 161 71 8 52 8 9 3 10

* Washington State DOT refers to these terminals as ET-31 terminals, i.e., ET-Plus terminals used with 31-inch guardrail.

** Numbers in parentheses are not included in column total. They indicate the data source of the Phase 6A cases.

*** Phase 6A cases were drawn from Phases 1A, 3A, 3B, and 4C. Those cases are included in the number of cases screened by FHWA for those phases.

1A—National Motor Vehicle Crash Causation Survey (NMVCCS). The NMVCCS was a congressionally mandated, on-scene crash study conducted to better understand the "causes" of crashes. NMVCCS investigated a nationally representative sample of crashes between 2005 and 2007. The National Highway Traffic Safety Administration (NHTSA) makes NMVCSS data accessible through http://www-nass.nhtsa.dot.gov/nass/nmvccs/SearchForm.aspx. The database includes crash reports and photos of crash scenes for viewing post-crash conditions of w-beam guardrail terminals as a means to better understand their in-service performance. FHWA searched the database for roadway departure impacts of selected w-beam guardrail terminals. The search yielded more than 700 cases involving roadway departure, including 78 in the vicinity of w-beam guardrail terminals. Among these cases, FHWA identified 14 crashes involving ET-Plus or ET-2000 terminals that were reviewed. In addition, two crashes that involved the SKT and one that involved a FLEAT were reviewed during Phase 6A.

2A—Harman. On December 3, 2014, FHWA received a letter from Boies, Schiller & Flexner LLP, which represents Joshua Harman, transmitting a spreadsheet listing 231 crash cases as well as data on those cases. The letter stated that the data on that spreadsheet represented "accidents of all 4-inch ET-Plus crashes that we are aware of in which the ET-Plus failed to operate as intended." The data varied by crash. Some included photographs of a damaged terminal and/or photographs of damaged vehicles involved in crashes, and others included supporting documentation such as crash reports, news articles, and legal documents. In its initial screening of these data, FHWA identified 156 crash cases in which the photographic evidence confirmed an ET-Plus 4-inch terminal was involved in the crash. Among these cases, FHWA identified 14 crashes that appeared to involve severe injuries, vehicle compartment intrusion, vehicle occupant compartment penetration, spearing, rollover, snagging of rail, or otherwise appeared to be unusual or extreme; these crashes were targeted for further review. Appendix C provides an overview of the 231 crash cases.

2B—Missouri DOT, First Submission. The Missouri DOT provided information on 34 crash cases involving terminals in the State. The information included crash reports and photographs. In its initial screening of this information, FHWA identified 11 cases involving ET-Plus terminals. The other cases involved other terminal types or terminal types that could not be determined from the available information, or did not involve a terminal.

3A—National Automotive Sampling System, Crashworthiness Data System (NASS CDS). The NASS CDS has detailed data on a representative, random sample of approximately 5,000 minor, serious, and fatal crashes per year involving passenger cars, light trucks, vans, and utility vehicles. Trained crash investigators obtain data from crash sites and then those data are quality controlled and become part of the permanent NASS CDS record available at http://www-nass.nhtsa.dot.gov/nass/cds/. FHWA queried the NASS CDS for the years 2010 through 2013, identified 56 cases in which w-beam terminal systems were impacted during roadway departure crashes, and then conducted photographic analysis of those cases. FHWA could positively identify the terminal type in 35 of these cases. Of these, the 10 cases involving ET-Plus terminals were reviewed, and one involving a FLEAT terminal was reviewed during Phase 6A.

3B—Missouri DOT, Second Submission. The Missouri DOT provided a second submission of information on 38 crash cases. Two of these cases were "identified by motorists in Missouri." The data for the two citizen-identified cases, which each included two photographs, were insufficient for detailed review. The 36 remaining crash cases included 32 cases involving an ET-Plus or ET-2000 terminal. These cases moved forward for detailed review. One case involved an SKT terminal that was reviewed during Phase 6A. In the remaining 3 cases, the terminal type either could not be identified or was not an energy-absorbing type of terminal.

4A through 5A—Crash Cases Submitted through Federal Register Notice. In a December 24, 2014 Federal Register Notice and Request for Information, FHWA requested data and information regarding the in-service performance of the ET-Plus guardrail terminal, including any data and information concerning vehicle crashes involving the ET-Plus. FHWA specifically sought crash reports, photographs of damaged ET-Plus devices at crash scenes, photographs of vehicles at crash scenes that impacted ET-Plus devices, and crash reconstruction reports with corresponding data. All comments submitted to the Federal Register docket in response to this request are available at https://www.federalregister.gov/articles/2014/12/24/2014-30081/ET-Plus-guardrail-end-terminal. Several entities provided data and information that were sufficient to evaluate the performance of the terminal. These include:

Crash Case Review Process

The crash case review process included six primary components:

  1. Initial screening of all crash case data by FHWA staff
  2. Detailed analysis of selected crash cases by FHWA staff
  3. Detailed analysis of selected cases by independent expert reviewers
  4. Detailed analysis of selected cases by State DOT representatives on Task Force
  5. Task Force discussion of key cases
  6. In-person meeting of the Task Force and independent expert reviewers

Component 1: Initial Screening of All Crash Case Data by FHWA

For each of the data sources, FHWA conducted an initial screening of the crash cases. The primary purpose of the initial screening was to determine whether there were sufficient data to evaluate:

A variety of information is important in order to accurately determine whether a terminal performed as intended, including data on:

Accurate information on these details, along with an analysis of the guardrail terminal and involved vehicle(s), would be necessary in order to effectively determine whether the placement, installation, or maintenance of the guardrail terminal had an unintended effect on the severity outcome of the crash.

The types of data sources that might provide such information include:

The post-crash photos must be viewed with caution. After crashes, rescue or maintenance crews need to clear the deformed rail and/or terminal from the roadway. Post-crash photos may not show the vehicle and rail damage locations immediately after impact.

None of the cases provided the complete information necessary to make a full, definitive evaluation of the crash. For some cases, however, there was adequate information to allow a reasonably informed evaluation of the performance of the terminal. Those cases for which the available data were not deemed sufficient to permit a reasonably informed evaluation did not move forward to the next phase of review.

Over time, the review focused increasingly on cases that were most likely to provide evidence of performance limitations in terminals, i.e., cases that resulted in a fatality or serious injury outcome and/or may have involved occupant compartment deformation, occupant compartment penetration, spearing, rollover, sudden deceleration, snagging of rail, or otherwise appeared to be unusual or extreme. Therefore, many cases in which the "terminal appeared to perform as intended" and in which the crash outcome was less severe did not move forward to the next phase of review.

Appendix D includes a listing of all cases screened by FHWA, identifies those cases sent forward to the independent expert reviewers and the State representatives on the Task Force for detailed review, and summarizes the reason the remaining cases were not sent forward. Appendix E includes several examples of those remaining cases to illustrate typical reasons cases were not sent forward to the Task Force for review.

Component 2: Detailed Analysis of Selected Cases by FHWA

FHWA staff conducted detailed reviews of the data available for those cases passed forward from the initial screening. The reviewers documented their evaluation of the type of terminal and the behavior of the vehicle and terminal during impact. FHWA also recorded a summary assessment of the performance of the terminal in one of five categories:

There were many discussions over the course of the review on the meaning of "perform as intended" and similarly for other assessment categories. As noted under the section that discusses Component 5 of the effort, these summary assessments simply provided a "first cut" of the device's performance, and the Task Force did not view them as a conclusive determination of the outcome of the cases.

Component 3: Detailed Analysis of Selected Cases by Independent Expert Reviewers

FHWA contracted with the University of North Carolina Highway Safety Research Center (UNC HSRC) to manage a review of the 161 crash cases by independent expert reviewers and charged the Center with selecting as reviewers three individuals who:

The UNC HSRC selected as reviewers:

The independent expert review process was conducted as follows:

This process was repeated for each of the data sources. Figure 2 provides an example of the instructions FHWA provided to the UNC HSRC for one of the data sources.

Figure 2 - Sample Instructions to Independent Expert Reviewers

Independent Expert Reviews of Crash Cases Involving Guardrail Terminals

Phase IIIA

Instructions to Reviewers

Background:

The Federal Highway Administration (FHWA) is conducting a safety analysis of guardrail terminals. As part of that analysis, FHWA identified crash cases from several sources that may have occurred within the vicinity of a terminal of interest. For each case, FHWA staff assessed the type of terminal in the vicinity of the crash; what, if any, role the terminal played in the crash outcome; whether or not the terminal appears to have performed as designed/intended; and whether the available data suggest any design issues with the terminal.

Phase IIIA Review:

Phase IIIA involves a review of 10 crash cases from NHTSA's National Automotive Sampling System (NASS) Crashworthiness Data System (CDS). FHWA identified these cases in the vicinity of a terminal of interest from the online NASS CDS Case Viewer. FHWA is providing a review form that provides a hyperlink to the online NASS CDS case file, a summary of FHWA staff's evaluation, and a cell for reviewers to document their assessment of the crash case. Within the online case file, reviewers have several options to view Text and Images Only, create a Print Friendly Version of Case, or Download Case.

Reviewers should understand that FHWA is providing links to data directly from the source. These data do not include information on the pre-crash condition of the terminal, or what may have been done to the damaged terminal by first responders or maintenance workers. There is no information on whether the terminal was installed or maintained correctly, or whether it had been damaged and left unrepaired prior to the crash in question, beyond evidence that may be visible in the post-crash photos.

FHWA seeks independent expert review of these 10 cases, including FHWA staff's written evaluation. Pertinent questions include:

  • The type of terminal in the vicinity of the crash.
  • What, if any, role the terminal played in the crash outcome.
  • Whether or not the terminal performed as designed/intended.
  • Whether the available data suggest any design issues with the terminal.

Estimated Level of Effort:

FHWA's estimate of the time required to review the 10 cases is approximately 1 hour per case. FHWA estimates an additional 4 hours may be required for each reviewer to document their findings.

Component 4: Detailed Analysis of Selected Cases by State DOT Representatives on Task Force

For each data source, FHWA transmitted the data files for the same selected crash cases to the State DOT representatives on the Task Force. The Task Force agreed to the screening method FHWA used to screen the cases down to the 161 cases for the Task Force's review. In addition, FHWA provided the Task Force members both the FHWA and independent expert reviewer evaluations in a format that enabled individual members to decide whether they wished to view those evaluations before, during, or after their own review of the cases.

The AASHTO co-chair of the Task Force divided the nine State DOT representatives into two groups and randomly assigned each case to one of the groups. Some State DOT representatives, however, elected to review all of the cases. The AASHTO co-chair developed a review form that each State DOT representative completed for each case. The review form requested the information listed in Table 10 for each case. In this form, terminal performance had three categories:

The State DOT representatives completed their reviews independently and submitted their completed review forms to FHWA. FHWA compiled the individual reviews in a spreadsheet.

Table 10 - Data Elements on State DOT Representatives Review Form

• Maximum injury level of crash • Crash: Impact into rear of vehicle • Vehicle: Vehicle sliding at impact (non-tracking) • Terminal: Rail too high
• Posted Speed Limit of facility • Crash: Shallow impact angle • Vehicle: Occupant compartment penetration • Terminal: Rail too low
• Terminal type • Crash: Outcome could have been worse without barrier present • Terminal: Rail rupture • Terminal: Missing/wrong hardware
• Terminal post type • Weather conditions: Raining at time of crash • Terminal: Rail bending back onto itself (kinking/knuckling) • Terminal: Damaged prior to impact
• Terminal head engaged during crash? • Weather conditions: Snowing at time of crash • Terminal: Rail travel impeded through terminal head • Terminal: Buildup of soil under rail
• Terminal performance (Three categories) • Weather conditions: Snow/ice present • Terminal: Minimal extrusion of rail through head • Other
• Not as Intended Description • Weather conditions: Buildup of snow/ice under rail • Terminal: Excessive ground slope • Additional Comments
• Crash: Other impact prior to or after collision with barrier • Vehicle: Not representative of TL-3 test vehicle • Terminal: Excessive flare rate  
• Crash: Rollover after impact • Vehicle: Modifications made to vehicle • Terminal: Curved flare used instead of straight flare  
• Crash: Occupant unbelted • Vehicle: Excessive speed • Terminal: Straight flare used instead of curved flare  
• Crash: Occupant ejected • Vehicle: Vehicle rolling at impact • Terminal: Lack of grading blister/shelf  
• Crash: Impact into side of vehicle • Vehicle: Vehicle pitching at impact • Terminal: Installed behind curb  

Component 5: Task Force Discussion of Key Cases

FHWA identified cases in which at least one of the FHWA staff, independent expert reviewers, or State DOT representatives categorized the terminal's performance as "not as intended," "unexpected," or "impacted under extreme conditions." The Task Force discussed those cases during weekly conference calls with the goal of identifying performance limitations.

It became apparent during the early discussions of individual cases that the two or three word summary statements about a terminal's performance were useful for screening the cases that merited further attention, in the form of group discussion, but that they had limited value beyond initial screening. Because of the myriad of complicating factors and the lack of detailed information on conditions before and during impact with a terminal, the summary statements were insufficient for characterizing the cases. As the discussions continued, the Task Force increasingly focused on the central issue of its charge: performance limitations.

Component 6: In-Person Meeting of Task Force and Independent Expert Reviewers

On May 4-5, 2015, the Task Force members and the independent expert reviewers met to review and discuss the key 161 crash cases. The group spent considerable time reaching consensus on whether or not terminals exhibited performance limitations in individual cases, identifying commonalities in performance limitations across cases, and developing meaningful categorizations of observed performance limitations. The Task Force findings are organized according to this categorization.

TASK FORCE FINDINGS

Review of Crash Cases

At the in-person meeting, the Task Force and the independent expert reviewers met to discuss whether there are performance limitations associated with extruding w-beam guardrail terminals. The group reviewed and discussed cases the Task Force and expert reviewers identified that exhibited potential performance limitations of extruding w-beam guardrail terminals. During review of the cases, the group came to a consensus on the potential performance limitations the cases exhibited, and which cases best illustrated each limitation based on the available information. Through review of the cases, a final set of performance limitations emerged from the analysis.

The Task Force's analysis nevertheless had inherent limitations. For a number of cases, it was not possible to determine whether performance limitations existed due to the limited available information. It was not always possible to infer pre-crash conditions or to conclusively determine a terminal's behavior during a crash from post-crash photography and reporting. Pre-crash photos of the terminal were rarely provided, and many cases lacked post-impact photos of the vehicle or of the terminal that were of sufficient quality to be useful. Finally, some cases completely lacked any photos.

Finally, the Task Force's review and analysis of crash cases were not intended to be full crash reconstructions. None of the Task Force members or expert reviewers are certified crash reconstructionists.

Performance Limitations

Performance limitations are factors in a real-world crash environment that can contribute to the unsuccessful performance of a roadside safety hardware device. As indicated in MASH, guardrail terminals "are generally developed and tested for selected idealized situations that are intended to encompass a large majority, but not all, of the possible in-service collisions." Satisfactory performance can typically be expected for collision conditions similar to the test conditions. However, the performance of these devices is dictated by physical laws, vehicle stability, vehicle crashworthiness, and the site conditions of these real-world crashes. The greater the crash conditions differ from the test conditions, the more likely the possibility that performance will be outside of the desirable limits.

As noted in both NCHRP Report 350 and MASH, even the most carefully researched roadside hardware device has performance limitations dictated by many factors. Limitations may be exhibited once these devices, having met all recommended test and evaluation criteria, are installed under real-world conditions. As noted, seemingly insignificant site conditions such as curbs, slopes, and soft soil conditions can contribute to the unsuccessful performance of a safety feature for some impact conditions. It is to be expected that certain features, meeting all recommended test and evaluation criteria, will have untested "windows of vulnerability" in service.

In its review of cases, the Task Force identified several potentially harmful occurrences associated with certain guardrail terminal crashes. These occurrences include: sudden deceleration, rollover, occupant compartment penetration, and occupant compartment deformation. Crash cases noted as having these occurrences were used to help identify performance limitations.

Both sudden deceleration and rollover of a vehicle can result in injuries through occupant contact with interior surfaces of the vehicle or through ejection of an occupant from the vehicle. Occupant compartment penetration involves a portion of the guardrail entering the passenger area of the vehicle and can result in injuries through occupant contact with the penetrating rail. Occupant compartment deformation occurs when the force of a guardrail impact deforms the interior structure of a vehicle's passenger area. Injuries can result from occupant contact with the intruding structure.

Members of the Task Force identified six primary performance limitations of extruding w-beam guardrail terminals. These limitations are classified into two general categories: impact conditions and installation conditions.

The impact conditions that the Task Force identified as performance limitations include:

The installation conditions identified as performance limitations include:

The following section discusses the impact conditions that were identified as performance limitations. The findings are based on the Task Force's observations during its review of the crash cases combined with the collective engineering judgment of the Task Force members. There is a general description first of these impact conditions followed by crash cases exhibiting the different impact conditions.

Impact Condition: Side Impact

Side impacts include crashes where any side portion of a vehicle is the first portion of the vehicle to make contact with a guardrail terminal. This situation typically occurs after a vehicle has lost control and leaves the roadway in a rotating or non-tracking manner. Side impacts into terminals may result in four potentially harmful occurrences: occupant compartment penetration, occupant compartment deformation, sudden deceleration, and rollover.

Side impacts pose a risk of occupant compartment deformation, especially in those cases where first contact occurs at one of the doors. Extruding w-beam guardrail terminals were developed to absorb a certain amount of energy over a certain distance. This requires them to exert a very strong force to slow an impacting vehicle. In a frontal impact, these strong forces act well in front of the occupants in a space that includes crumple zones, an engine, and significant frames and structures. When the same high forces are applied to the side of a vehicle, there is often very little structure to resist these forces, and significant deformation can occur. Additionally, an occupant may be in very close proximity to the powerful impact with the terminal.

Because side impacts are typically associated with vehicle rotation, they have the potential to stop the process of guardrail extrusion very early in an impact event by bending or knocking the impact head out of line with the downstream run of guardrail. Once this occurs, a kink in the rail can form, and the kink may make contact with, and penetrate through, the side of the vehicle. Penetration risk is increased because the side of the vehicle presents a wider target for a kink to penetrate into than does the front of a tracking vehicle. Additionally, the sides of most passenger vehicles are relatively weak, whereas the front of most vehicles provides the protection of an engine block, bumper, suspension, and firewall. The vehicle's rate of rotation, the direction of the vehicle's momentum, the initial point of contact, and the vehicle's speed can each affect whether a guardrail kinks, how much guardrail is extruded before it kinks, and where the kink contacts the vehicle, if at all.

Seat belts and most airbags are designed to restrain motorists against forward motion. But unless the vehicle is equipped with side airbags, sudden decelerations experienced during a side impact may result in occupants moving sideways and striking one of the vehicle's pillars.

Side impacts have an increased risk of rollover because a vehicle in a lateral skid is subject to higher lateral tire forces and may be more prone to tripping on the terminal. In addition, portions of the terminal that come into contact with the vehicle may act as a fulcrum to introduce a tripping moment on the vehicle.

The images in Figure 3 show one possible sequence of events during a side impact that can result in occupant compartment deformation.

Figure 3 - Possible side impact scenario

Figure 3 shows images of one possible sequence of events during a side impact that can result in occupant compartment deformation.

Impact Condition: Head-on/Shallow-Angle Corner Impacts

The next impact condition that may indicate a performance limitation of extruding w-beam guardrail terminals is a head-on impact that occurs near the corner of the vehicle. These types of crashes occur when a vehicle encounters a terminal in a head-on or nearly head-on manner (i.e., at a shallow angle), and when first contact with the impact head takes place near one of the edges of the front of the vehicle, in one of the headlight regions. These impacts differ from crash tests in NCHRP Report 350 or MASH in that the initial contact occurs farther outboard on the front of the vehicle than the quarter point.

Head-on impacts near the corner of the vehicle have the potential to become problematic because the force of the vehicle pushing on the guardrail (located at the vehicle's center of gravity) is significantly out of line with the opposing force of the guardrail pushing on the vehicle. This induces a rotation of the vehicle (as highlighted in Figure 4) that bends the impact head to the side, which kinks the rail at the end of the inlet chute. The impact head may then fold across the front of the vehicle, subjecting the vehicle to the kink and the entirety of the downstream run of guardrail. With the loss of the energy-absorbing function of the impact head, as the vehicle continues its movement downstream, the rail may either push farther into the vehicle, or form kinks downstream of the impact due to buckling of the rail.

Figure 4 – Rotation induced by corner impact

Figure 4 shows Head-on impacts near the corner of the vehicle have the potential to become problematic because the force of the vehicle pushing on the guardrail (located at the vehicle’s center of gravity) is significantly out of line with the opposing force of the guardrail pushing on the vehicle. This induces a rotation of the vehicle that bends the impact head to the side, which kinks the rail at the end of the inlet chute.

Figures 5 and 6 depict the difference between kinking of the guardrail due to bending, and kinking of the guardrail due to buckling. An angle impact at the nose of the terminal will likely push the terminal to the side, causing the system to bend, creating a kink in the rail as shown in Figure 5. Figure 6 shows a load applied at the nose of the terminal but the w-beam rail that is downstream does not have the necessary stiffness to resist bending. In either case, the terminal is no longer able to travel down the rail and absorb the energy of the crash. The vehicle may continue forward and come in contact with the kink in the rail.

Figure 5 - Example of kinking of the guardrail due to bending

Figure 5 shows kinking of the guardrail due to bending.

Figure 6 - Example of kinking of the guardrail due to buckling

Figure 6 shows kinking of the guardrail due to buckling.

The reaction of the vehicle to these corner-type impacts will vary based on mass and speed. However, in general, smaller mass vehicles have a lower moment of inertia and will rotate about the rail more readily, which may expose the side of the vehicle to either the first kink in the rail or a subsequent, downstream kink. Higher mass vehicles have higher moments of inertia and tend to rotate about the rail more slowly.

The images in Figure 7 show one possible sequence of events during a head-on corner impact with a smaller mass vehicle that could result in occupant compartment deformation and/or penetration. The degree of offset, the direction of the vehicle's momentum, the initial point of contact, and the vehicle's speed and mass will each affect the outcome of the crash.

Figure 7 - Head-on/shallow-angle corner impact scenario

Figure 7 shows one possible sequence of events during a head-on corner impact with a smaller mass vehicle that could result in occupant compartment deformation and/or penetration.

Impact Condition: Head-on/Shallow-Angle High-energy Impacts

Another impact condition that may indicate a performance limitation of extruding energy-absorbing terminals is a head-on/shallow-angle high-energy impact. These types of crashes occur when the kinetic energy of the impacting vehicle exceeds the test level 3 impact conditions of NCHRP Report 350 under which the terminal was crash tested, and the angle of impact is shallow or nearly head-on. The kinetic energy can be exceeded through an impact involving a vehicle with high mass, a vehicle with excessive speed, or a vehicle with both high mass and excessive speed. In general, "excessive speed" is defined as speeds above 62 mph (100 km/h) and "high mass" is defined as vehicle mass greater than 4,400 pounds (2000 kg).

Head-on/shallow-angle high-energy impacts into terminals may result in the impacting vehicle remaining engaged with the impact head for an extended time period. With extruding terminals that are designed to absorb energy while being pushed along the rail, it is likely very rare that a vehicle's path and the terminal's resistance would remain perfectly aligned. Therefore, the longer the vehicle remains engaged with the impact head, the chances increase for minor perturbations in the extrusion process to develop, resulting in misalignment of the impact head with respect to the direction of the vehicle's momentum. As observed during crash tests, extruding energy-absorbing terminals have an inherent ability to correct and overcome minor misalignments. However, any misalignment beyond a certain threshold can cause the rail to bend.

Figure 8 - Head-on/Shallow-angle high-energy impact scenario

Figure 8 shows one possible sequence of events during a high-energy, head-on/shallow-angle impact that may result in occupant compartment deformation and/or penetration.

The images in Figure 8 show one possible sequence of events during a high-energy, head-on/shallow-angle impact that may result in occupant compartment deformation and/or penetration. The angle of impact, the initial point of contact, and the vehicle's speed and mass will all affect the outcome of the crash.

Minor perturbations in the extrusion process may occur due to several factors, including the vehicle traveling over downed posts, steering or braking inputs applied by the driver, rail splices and bolts passing through the impact head, or damaged sections of rail passing through the impact head. The Task Force noted one phenomenon that had the potential to damage the rail during an impact event: vertically out-of-plane impacts.

As illustrated in Figure 9, high contact on an extruding terminal's face could induce a rotational force that will cause the inlet end of the chute to move downward. The same can also be true of a low impact moving the chute upwards as contact is made. If the rotation is forceful enough, the top corrugation of the w-beam may be crushed down or the bottom corrugation may be crushed up. In an extreme case, rotation from a high contact may cause the bottom of the inlet end to strike the ground underneath the terminal, potentially stopping the extrusion process.

Figure 9 - Example of a vertically out-of-plane impact

Figure 9 shows how a high contact on an extruding terminal’s face could induce a rotational force that will cause the inlet end of the chute to move downward.

The cross-section drawings in Figure 10 correspond to the illustrations in Figure 9. The cross-sections in red represent what may happen to the w-beam rail as it passes through an extruding terminal after the top of the w-beam is deformed by the inlet end of the terminal early in the crash event.

Figure 10 - Example sections of a vertically out-of-plane impact
(see Figure 9 for section cuts)

The cross-section drawings in Figure 10 correspond to the illustrations in Figure 9. The cross-sections in red represent what may happen to the w-beam rail as it passes through an extruding terminal after the top of the w-beam is deformed by the inlet end of the terminal early in the crash event.

Crash Cases Exhibiting Performance Limitations: Impact Conditions

This section summarizes the detailed reviews of crash cases that best illustrate the performance limitations related to impact conditions. Table 11 lists the 15 crash cases that illustrate the identified performance limitations. The crash narratives for the cases were developed based on all available information for a particular crash (not just the narrative the police officer or crash investigator provided). The set of illustrations the Task Force developed for these cases depicts its interpretation of the likely sequence of events in the crash. The Task Force developed illustrations for crash cases for which enough information existed to approximate (i.e., likely not exact) one possible scenario for the sequence of events. These illustrations for all of the crash cases in the report should not be interpreted as crash reconstructions. They were inferred from photos of crash scene, damaged terminal, and damaged vehicle but some assumptions were made given the limitations of the data available.

Table 11 - Crash Case Performance Limitations and Potentially Harmful Occurrences

Primary
Performance
Limitation

Case #

Device Type

Vehicle

Injury Severity

Potentially Harmful
Occurrence

Side Impact

1A004

ET-2000

Sedan

PDO*

Sudden deceleration

2B002

ET-Plus 4-inch

SUV

Fatal

Rollover

2B010

ET-Plus 4-inch

Sedan

Unknown

Sudden deceleration

3A007

ET-Plus 5-inch

Pickup

Unknown

Rollover

3A010

ET-Plus 4-inch

Sedan

Unknown

Occupant compartment
deformation

5A002

ET-Plus 4-inch

Sedan

Fatal

Rollover

6A002

SKT

Sedan

Incapacitating

Sudden deceleration

Head-on / Shallow-
angle Corner Impact

2A018

ET-Plus 4-inch

Truck

Unknown

Penetration

2B008

ET-Plus 4-inch

Sedan

Serious injury

Penetration

2B009

ET-Plus 4-inch

Sedan

Fatal

Penetration

5A001

ET-Plus 5-inch

SUV

Incapacitating injury

Penetration

6A020

FLEAT

Pickup

Minor injury

Penetration

Head-on /Shallow-
angle High-energy Impact

1A009

ET-Plus 5-inch

Pickup

PDO

Near Penetration

5A009

ET-Plus
(4-inch or 5-inch)

Truck

Fatal

Penetration

6A021

SKT

SUV

Fatal

Penetration

* PDO: Property Damage Only

Case #1A004

Narrative:

This single-vehicle crash occurred during daylight hours on a right-curving entrance ramp to a 4-lane divided interstate highway with a speed limit of 70 mph. At the time of the crash, it was cloudy and the roadway was wet from a recent rain event.

The subject vehicle, a 2007 Pontiac G6 sedan, lost control negotiating the curved entrance ramp. The available evidence suggests the vehicle fishtailed and began to rotate clockwise, skidded off the right side of the highway, left side leading, and struck an ET-2000 terminal with its left rear side. Approximately 10 feet of rail was extruded through the impact head before the terminal gated and allowed the vehicle to pass through. The force of the impact with the terminal deformed the left rear passenger door, door frame, and quarter panel. The vehicle then rotated back in the counterclockwise direction, slid down an embankment, and came to rest.

While there were no injuries associated with this particular crash, it does demonstrate the extreme forces involved in such an impact. Injuries could have resulted from intrusion of the door panel, contact with the side window glass, or sudden deceleration. The potentially harmful occurrence in this case appears to be sudden deceleration.

The non-tracking side-impact conditions of this crash were beyond what would be tested under NCHRP Report 350 and MASH.

Photos:

Photo 1 - Approach to terminal and final rest of vehicle

Photo 1 showing damaged terminal head for Case #1A004, caption reads 'Approach to terminal and final rest of vehicle.'

Photo 2 – Close-up of end terminal

Photo 2 showing damaged terminal head for Case #1A004, caption reads 'close up of end terminal.'

Photo 3 - Damage to vehicle

Photo 3 showing damaged vehicle for Case #1A004, caption reads 'Damage to vehicle.'

Figure 11 – Police Report Crash Diagram

Figure 11 shows Police report crash diagram for Case #1A004.

Figure 12 - Illustration of one possible crash sequence

Figure 12 shows illustration of one possible crash sequence for Case #1A004.

Case #2B002

Narrative:

This crash occurred approximately one hour before sunrise on a clear, mid-January morning. The subject vehicle, a 1987 Ford Bronco II, was traveling on a tangent, dry, four-lane divided interstate highway when it was impacted from the left by another vehicle traveling in the same direction.

The available evidence indicates this impact caused the subject vehicle to lose control, initiating a clockwise rotation and sending it skidding toward the right side of the roadway, as evidenced by the skid marks shown in Photo 4. The vehicle had rotated nearly one-quarter turn by the time it exited the paved portion of the roadway, where it impacted a 4-inch ET-Plus terminal. The vehicle made first contact with the terminal in the area of the driver's side front tire. This contact with the leading edge of the terminal left vertical indentations in the fender just above the tire, as shown in Photo 5.

Approximately two feet of rail was extruded through the impact head before the angle of the impact bent the rail at the inlet chute, causing a kink to form as shown in Photo 6. This kink contacted the vehicle in the driver's door, crushing the door inward as shown in Photo 7, and initiating a roll. The vehicle rolled over one complete rotation, ejecting the two unbelted occupants. The driver sustained a fatal injury and the passenger sustained an incapacitating injury as a result of the crash.

The potentially harmful occurrence in this case appears to be rollover, and the non-tracking side-impact conditions of this crash were beyond what would be tested under NCHRP Report 350 and MASH.

Photos:

Photo 4

Photo 4 shows approach roadway for Case #2B002

Photo 5

Photo 5 shows damaged vehicle for Case #2B002

Photo 6

Photo 6 shows damaged guardrail for Case #2B002

Photo 7

Photo 7 shows approach roadway for Case #2B002

Figure 13- Police Report Crash Diagram

Figure 13 shows Police Report Crash Diagram for Case #2B002.

Figure 14 - Illustration of one possible crash sequence (Part A)

Figure 14 shows illustration of one possible crash sequence with no vehicle roll over for Case #2B002.

Figure 15 – Illustration of one possible crash sequence (Part B)

Figure 15 shows illustration of one possible crash sequence with vehicle roll over for Case #2B002.

Case #2B010

Narrative:

This single-vehicle crash occurred on a suburban interstate facility with four through lanes and one auxiliary (entrance ramp) lane. The speed limit along this portion of interstate is 60 mph. The alignment at the point where the vehicle left the roadway was straight and the grade was nearly flat (-1%). At the time of the crash, in the very early hours of a mid-March morning, the weather was clear and the roadway was dry.

The driver of the subject vehicle, a 2000 Toyota Camry, failed to negotiate a merge into the right travel lane from an auxiliary entrance ramp lane that was ending. The vehicle ran off the road to the right onto the soil shoulder. The available evidence suggests that the driver was attempting to steer the vehicle back onto the roadway when the right side of the vehicle clipped the inside edge of an ET-Plus terminal. Upon making contact with the terminal, the vehicle began to rotate clockwise, and slid along the roadway approximately 200 feet before the driver was able to regain control of the vehicle.

Based on the tire impressions shown in Photos 8 and 9, the available evidence indicates the vehicle appeared to have been heading back toward the roadway at a shallow angle just prior to impact. The initial impact with the inside edge of the terminal head occurred near the handle on the right side front door, just slightly in front of the B-pillar as shown in Photo 10. After impacting the right front door, the vehicle remained in contact with the terminal head, the right rear door was torn away from its hinges and the door was pushed rearward, exposing the rear occupant's compartment. After extruding approximately 8 to 10 feet of guardrail, the system bent and kinked toward the roadway, and the terminal head disengaged from the vehicle. After the photos shown below, a set of illustrations the Task Force developed is presented that depicts its interpretation of one possible scenario of the likely sequence of events in this crash.

The potentially harmful occurrence in this case appears to be sudden deceleration, and the side-impact conditions of this crash were beyond what would be tested under NCHRP Report 350 and MASH.

Photos:

Photo 8

Photo 8 shows approach roadway for Case #2B010

Photo 9

Photo 9 shows approach roadway with tire impressions for Case #2B010

Photo 10

Photo 10 shows damage to vehicle for Case #2B010

Figure 16 - Illustration of one possible crash sequence

Figure 16 shows illustration of one possible crash sequence for Case #2B010.

Case #3A007

Narrative:

This single-vehicle crash occurred on a four-lane divided highway at approximately 11:00 a.m. on a November day. The roadway was level and curving to the right, with a posted speed limit of 55 mph. At the time of the crash, the weather was clear, the roadway was dry, and it was daylight.

The driver of the subject vehicle, a 1997 Dodge Dakota, failed to negotiate the curve and departed the roadway to the left. As the driver attempted to steer the vehicle back onto the roadway, the available evidence appears to indicate the vehicle began to rotate clockwise and the left side of the vehicle contacted an ET-Plus guardrail terminal, just forward of the driver's side rear wheel. Contact with the terminal initiated a roll of the vehicle. Approximately 3 feet of guardrail was extruded through the impact head before the vehicle lost contact with the terminal. The truck rolled over and came to rest on its roof in the traveled lanes. The vehicle caught fire.

The available information contained only one photograph of a damaged terminal; the remaining photographs were of an undamaged terminal.

The potentially harmful occurrence in this case appears to be rollover, and the non-tracking side-impact conditions of this crash were beyond what would be tested under NCHRP Report 350 or MASH.

Photos:

Photo 11 - Repaired terminal at crash site

Photo 11 shows approach roadway for Case #3A007

Photo 12 - On-scene photo of terminal after impact

Photo 12 shows damaged end terminal for Case #3A007

Photo 13 - Crash scene after impact and vehicle roll

Photo 13 shows damaged vehicle for Case #3A007

Photo 14 - Damage near the left rear tire, the initial point of contact with terminal

Photo 14 shows damaged vehicle for Case #3A007

Figure 47 - Police Report Crash Diagram

Figure 47 shows police report diagram for Case #3A007

Case #3A010

Narrative:

This single-vehicle crash occurred at approximately 7:00 p.m. on a May evening on a 5-lane divided roadway. The roadway was straight and level. At the time of the crash, the weather was clear and the roadway was dry. It appears there was another vehicle entering the roadway at the on-ramp and the driver of the subject vehicle, a 1993 Oldsmobile Cutlass Supreme, took evasive maneuvers to avoid a collision. The available evidence indicates the driver lost control of the vehicle and began a counterclockwise yaw. The vehicle skidded off the roadway to the right (Photo 15) and struck an ET-Plus terminal. Photo 16 indicates the impact occurred on the right side in the rear passenger door area. The force of the impact deformed the door, and the inside of the door intruded into the occupant compartment.

The terminal extruded approximately 19 feet of rail and halted the counterclockwise yaw. The vehicle remained in contact with the extruder head and began to spin clockwise. As the vehicle spun back onto the roadway, the rail bent and kinked toward the roadway, and the extruder head disengaged from the vehicle. After the photos and Police Report Crash Diagram shown below, a set of illustrations the Task Force developed is presented that depicts its interpretation of one possible scenario of the likely sequence of events in this crash.

The potentially harmful occurrence in this case appears to be occupant compartment deformation. The non-tracking side-impact conditions of this crash were beyond what would be tested under NCHRP Report 350 or MASH.

Photos:

Photo 15 - Skid marks of vehicle at point of impact

Photo 15 shows skid marks of vehicle at point of impact for Case #3A010

Photo 16 – Point of end terminal contact

Photo 16 shows damaged terminal for Case #3A010

Figure 58 - Police Report Crash Diagram

Figure 58 shows police report diagram for Case #3A010

Figure 69 - Illustration of one possible crash sequence

Figure 69 shows illustration of one possible crash sequence for Case #3A010

Case #5A002

Narrative:

This crash occurred mid-morning on a December day on a two-way, undivided roadway. The posted speed limit of the roadway is 65 mph. The roadway curves to the left on an uphill grade, and guardrail lines both sides of the roadway. The crash involved one vehicle, a 1992 Ford Taurus, containing three occupants. At the time of the crash, it was daylight, raining, and the roadway was snow-covered with some ice/frost present.

As the vehicle attempted to traverse the curve, the driver lost control on the icy pavement. The vehicle started to yaw in a clockwise direction, departed the roadway to the right, and struck a guardrail terminal near its front left corner. A minimal amount of rail was extruded through the terminal before the rail bent and a kink was formed. It appears that the kink contacted the side of the vehicle just aft of the rear passenger door. Contact with the kink caused a tripping moment, and the vehicle overturned, coming to rest on its roof, off of the roadway.

A set of illustrations the Task Force developed is presented that depicts its interpretation of one possible scenario of the likely sequence of events in this crash.

The potentially harmful occurrence in this case appears to be a rollover. The non-tracking side-impact conditions of this crash were beyond what would be tested under NCHRP Report 350 or MASH.

Photos:

Photo 18

Photo 18 shows damaged terminal & vehicle for Case #5A002

Photo 19

Photo 19 shows damaged terminal for Case #5A002

Photo 20

Photo 20 shows damaged vehicle for Case #5A002

Photo 21

Photo 21 shows damaged vehicle for Case #5A002

Photo 22

Photo 22 shows slope damaged by vehicle for Case #5A002

Figure 20 - Police Report Crash Diagram

Figure 20 shows police report diagram for Case #5A002

Figure 21 - Illustration of one possible crash sequence (Part A)

Figure 21 shows illustration of one possible crash sequence for Case #5A002

Figure 22 - Illustration of one possible crash sequence (Part B)

Figure 22 shows illustration of one possible crash sequence for Case #5A002

Case: 6A002

Narrative:

This crash occurred on a November afternoon on an entrance ramp to a four-lane expressway. The posted speed limit of the expressway was 55 mph. The entrance ramp consists of a 3.3% downward slope and a curve to the right with an approximate 370-foot radius. It was snowing at the time of the crash, with slush accumulation on the shoulders. Photos 19 and 20 show approach views of the crash scene.

The driver of the subject vehicle, a 1993 Saturn SL2, was entering the expressway via the entrance ramp, attempting to merge into the westbound traffic. The driver attempted to merge, but was unable to find a gap. Upon slowing the vehicle, the driver lost control and the vehicle began a clockwise spin. The vehicle then ran off the road to the right and contacted a guardrail terminal with the front driver's side door.

After impact, the vehicle rotated one-quarter turn, coming to rest facing the wrong direction. There was damage to the driver's side front door as a result of the impact (Photo 25) and minor damage to the left rear corner (Photo 26) from what appears to be additional contact with the guardrail prior to the vehicle coming to rest, as seen on the Police Report Crash Diagram. The terminal extruded a very small amount of rail and gated as the vehicle continued its rotation.

A set of illustrations the Task Force developed is presented that depicts its interpretation of one possible scenario of the likely sequence of events in this crash.

The potentially harmful occurrence in this case appears to be sudden deceleration. The non-tracking side-impact conditions of this crash were beyond what would be tested under NCHRP Report 350 or MASH.

Photos:

Photo 23

Photo 23 shows approach roadway for Case #6A002

Photo 24

Photo 24 shows approach roadway & damaged terminal for Case #6A002

 

Photo 25

Photo 25 shows damaged vehicle for Case #6A002

Photo 26

Photo 26 shows damaged vehicle for Case #6A002

Photo 27

Photo 27 shows damaged terminal for Case #6A002

Photo 28

Photo 28 shows damaged terminal for Case #6A002

Figure 23 - Police Report Crash Diagram

Figure 23 shows police report diagram for Case #6A002

Figure 24 - Illustration of one possible crash sequence

Figure 24 shows illustration of one possible crash sequence for Case #5A002

Case #2A018

Narrative:

A redacted police crash report and numerous photos of the crash site (taken six days after the crash) were provided for this case. However, photos of the installation prior to the crash, photos of the crash scene, and post-crash photos of the vehicle could not be obtained. Nor are the make and model of the subject vehicle known. Given the lack of information, it is not possible to develop a strongly reliable sequence of crash events, but one possible scenario is presented here and is depicted in the illustrations that follow.

This crash occurred on a 4-lane divided interstate in the late afternoon of an October day. The speed limit on the highway was 65 mph. The weather was clear, and the roadway was dry. The driver of the subject vehicle – a small truck according to the police crash report – apparently fell asleep and drifted off the road to the left, striking a 4-inch ET-Plus terminal. The crash report states that the truck ended up on the traffic side of the barrier and pointing roughly upstream, so it is likely that the terminal was first contacted near the left front corner of the truck. The guardrail was pushed through the head until a damaged section of rail reached the reducer portion of the head. Passage of this damaged rail through the reducer caused a brief spike in resistance to the extrusion process. The increased resistance overcame the column strength of the rail, causing it to buckle downstream at the fourth post. Once the rail buckled, it could no longer exert the force necessary to continue pushing the damaged section of rail through the head, and that movement stopped. With the loss of the extrusion process, the vehicle was exposed to the downstream run of rail, and the rail penetrated through the front of the vehicle into the driver's footwell area.

This was the only case the Task Force reviewed for which there appears to have been a high resistance to passage of the rail through the head of the terminal. While this behavior was likely caused by a damaged section of rail, the source and the extent of the damage could not be verified. It is possible that the rail was damaged prior to the impact event, or that it was damaged during the impact event from a vertically out-of-plane impact, as described earlier in this report.

The potentially harmful occurrence in this case appears to be occupant compartment penetration. The offset, head-on nature of this crash is similar to the parameters used in NCHRP Report 350 Test 3-30. However, the vehicle in the subject crash (a small truck) is likely heavier than the 820C test vehicle, and the offset of the impact from the centerline of the vehicle is probably greater.

Photos:

Photo 29

Photo 29 shows damaged terminal and rail for Case #2A018

Photo 30

Photo 30 shows damaged rail for Case #2A018

Photo 31

Photo 31 shows damaged terminal and rail for Case #2A018

Photo 32 - Post 5

Photo 32 shows damage to post No5 for Case #2A018

Photo 33 - Close-up of Post 5 base

Photo 33 shows close-up of damage to post No5 for Case #2A018

Photo 34- Bowing of reducer sides

Photo 34 shows damaged terminal and bowing of reducer sides for Case #2A018

Figure 25 – Police Report Crash diagram

Figure 25 shows police report diagram for Case #2A018

Figure 26 - Illustration of one possible crash sequence (Part A)

Figure 26 shows illustration of one possible crash sequence part A for Case #2A018

Figure 27 - Illustration of one possible crash sequence (Part B)

Figure 27 shows illustration of one possible crash sequence part B for Case #2A018

Case # 2B008

Narrative:

This single-vehicle crash occurred on a 65-mph interstate when the driver fell asleep with the cruise control set and drifted off the shoulder on the right side. It was early morning, the weather was clear, the pavement dry, and there was daylight.

Damage to the hood and front of the vehicle, a 2005 Chevy Impala, indicate that the vehicle struck the left edge of an ET-Plus terminal just inboard of the right headlight (Photo 35). Due to the vehicle's relatively moderate weight and the offset nature of the impact, the vehicle began to rotate clockwise about the terminal. Based on the available evidence, it appears this rotation caused a bend to form in the rail at the inlet chute after approximately 15 feet of rail had been extruded (Photo 36). The rail kinked, and the impact head flattened across the front of the vehicle. With the loss of the extrusion process, a second kink appeared to develop downstream and contacted the vehicle just behind the left front wheel (Photo 37). This kink penetrated into the occupant compartment through the lower portion of the driver's side firewall (Photo 38).

The potentially harmful occurrence in this case appears to be occupant compartment penetration. The offset, head-on nature of this crash is similar to the parameters used in NCHRP Report 350 Test 3-30. However, the vehicle in the subject crash is almost twice as heavy as the 820C test vehicle, and the offset of the impact from the centerline of the vehicle is greater. The increased momentum may have resulted in the vehicle not "moving out of the way" of the guardrail as readily. The vehicle's trajectory continued forward which exposed the vehicle to any downstream kinks that may have developed.

Photos:

Photo 35

Photo 35 shows damaged vehicle for Case # 2B008

Photo 36

Photo 36 shows damaged terminal for Case # 2B008

Photo 37

Photo 37 shows damaged vehicle for Case # 2B008

Photo 38

Photo 38 shows damaged vehicle interior for Case # 2B008

Figure 28 – Police Report Crash diagram

Figure 28 shows police report diagram for Case #2B008

Case #2B009

Narrative:

This single-vehicle crash occurred around 10:00 p.m. on a March night on a straight and level section of interstate highway. At the time of the crash, it was snowing, and the road surface was wet and slushy. Though the speed limit was 70 mph, only four of the timber posts were snapped, suggesting the subject vehicle, a 2001 Toyota Camry, was being operated at a reduced speed. The driver of the vehicle lost control, and the vehicle departed the roadway to the right in a non-tracking fashion, rotating clockwise.

Upon leaving the roadway, the vehicle impacted an ET-Plus guardrail terminal with its front left corner (Photo 39). Based on the available evidence, it appears due to the rotation of the vehicle and its movement away from the road, the impact head was pushed quickly aside, bending and kinking the rail at the inlet end of the chute. The kink made contact with the vehicle near the front edge of the driver's door and penetrated into the occupant compartment (Photo 40).

After the photos and Police Report Crash Diagram shown below, a set of illustrations the Task Force developed is presented that depicts its interpretation of one possible scenario of the likely sequence of events in this crash.

The potentially harmful occurrence in this case appears to be occupant compartment penetration. The offset, head-on nature of this crash is similar to the parameters used in NCHRP Report 350 Test 3-30. It is important to note that the photos suggest a head-on crash, while the police report crash diagram depicts a side impact crash.

Photos

Photo 39

Photo 39 shows damaged vehicle and terminal for Case #2B009

Photo 40

Photo 40 shows damaged vehicle and terminal for Case #2B009

Figure 29 - Police Report Crash Diagram

Figure 29 shows police report diagram for Case #2B009

Figure 30 - Illustration of one possible crash sequence

Figure 30 shows illustration of one possible crash sequence for case #2B009

Case #5A001

Narrative:

This single-vehicle crash occurred on a rural two-lane highway around 6:00 a.m. on a Saturday morning in late March. The road was essentially straight, but the grade was rising for an overpass. The speed limit was 50 mph. The weather was cloudy and the pavement was wet.

The subject vehicle, a 2001 Chevy Tahoe, was approaching the overpass when it departed the roadway to the right. The lack of any skid marks on the road (Photo #41) to indicate an avoidance maneuver or loss of control suggests that the driver may have fallen asleep, and the vehicle drifted off the road at a very shallow angle.

The vehicle impacted an ET-Plus terminal on its front right side, near the passenger-side headlight. Based on the available evidence, it appears the offset impact induced a clockwise rotation of the vehicle. Approximately 25 feet of guardrail was extruded through the impact head (Photo #42) before the rotation caused a bend to form in the rail at the entrance to the inlet chute. The rail kinked, and it appeared the impact head flattened across the front of the vehicle (Photo #43). With the loss of the extrusion process and the continued forward motion of the vehicle, kinks began to form in the guardrail downstream. At this time, the vehicle appeared to have rotated approximately one-quarter turn, one of the downstream kinks then made contact with the driver's side of the vehicle near the base of the A pillar, and penetrated into the occupant compartment (Photo #44).

After the photos and Police Report Crash Diagram shown below, a set of illustrations the Task Force developed is presented that depicts its interpretation of one possible scenario of the likely sequence of events in this crash.

The potentially harmful occurrence in this case appears to be occupant compartment penetration. The conditions of this crash were beyond what would be tested under NCHRP Report 350. The subject vehicle exceeds the mass of the 2000P test vehicle by approximately 10 percent, and the offset, nearly head-on impact is not represented by any NCHRP Report 350 crash test for a vehicle of this size.

Photos:

Photo 41

Photo 41 shows approach roadway for Case #5A001

Photo 42

Photo 42 shows damaged guardrail for Case #5A001

Photo 43

Photo 43 shows damaged guardrail and terminal for Case #5A001

Photo 44

Photo 44 shows damaged vehicle and guardrail for case #5A001

Figure 31 - Police Report Crash Diagram

Figure 31 shows police report diagram for case #5A001

Figure 32 - Illustration of one possible crash sequence (Part A)

Figure 32 shows illustration of one possible crash sequence part a for case #5A001

Figure 33 - Illustration of one possible crash sequence (Part B)

Figure 33 shows illustration of one possible crash sequence part b for case #5A001

Case #6A020

Narrative:

This single-vehicle crash occurred on a 70-mph interstate when the vehicle, a 2006 Chevy Silverado, left the roadway for unknown reasons and drifted off the shoulder on the left side. The crash occurred at approximately 10:00 p.m. on an October night when the weather was clear and the pavement was dry. The estimated speed of the vehicle at the time of the crash was reported as 70 mph. Based on the Police Report Crash Diagram and the tire tracks visible in Photo 45, the impact into the terminal appears to have occurred at a shallow angle.

The initial point of contact was near the front left corner (headlight area) of the vehicle. Based on the available evidence, it appears the FLEAT 350 terminal extruded very little rail before the offset impact kinked and fractured the guardrail. Photo 46 shows the terminal head separated from the rest of the rail and located beyond the final point of rest of the vehicle. This occurrence likely implies the terminal head and the guardrails (up to the first splice) separated in the early stages of the crash and were propelled downstream. It appears that the exposed end of the in-place guardrail penetrated into the occupant compartment through the lower driver's side firewall as the vehicle continued to move forward (Photo 47). Even though the impact occurred on the extreme left corner of the vehicle, the vehicle spun out in a clockwise direction, going behind the guardrail. This may be attributed to the slope of the ground behind the guardrail installation. The vehicle ultimately rotated nearly 180 degrees before coming to a stop behind the rail.

After the photos and Police Report Crash Diagram shown below, a set of illustrations the Task Force developed is presented that depicts its interpretation of one possible scenario of the likely sequence of events in this crash.

The potentially harmful occurrence in this case appears to be occupant compartment penetration. The conditions of this crash were beyond what would be tested under NCHRP Report 350. The subject vehicle exceeds the mass of the 2000P test vehicle by approximately 20 percent, and the offset, nearly head-on impact is not represented by any NCHRP Report 350 crash test for a vehicle of this size.

Photos:

Photo 45 - Approach trajectory of vehicle

Photo 45 shows approach roadway for Case #6A020

Photo 46 - Terminal and rail beyond vehicle point of rest

Photo 46 shows vehicle damage for case #6A020

Photo 47 - Rail visible in driver’s side footwell

Photo 47 shows vehicle interior damage for case #6A020

Photo 48 - Final rest of vehicle

Photo 48 shows vehicle & guardrail damage for case #6A020

Figure 34 – Police Report Crash Diagram

Figure 34 shows police report diagram for case #6A020

Figure 35 - Illustration of one possible crash sequence (Part A)

Figure 35 shows illustration of one possible crash sequence for case #6A020

Figure 36- Illustration of one possible crash sequence (Part B)

Figure 36 shows illustration of one possible crash sequence for case #6A020

Case #1A009

Narrative:

This crash occurred early on a March afternoon on a divided four-lane interstate within a curve to the left. The speed limit on the highway was 65 mph, and there were no adverse weather conditions at the time of the crash. It appears that the driver of the subject vehicle, a Ford F-150 SuperCab pickup, may have fallen asleep and ran off the right side of the road, impacting a guardrail terminal. No braking was apparent from the post-crash photos, so it is likely that the impact speed was close to 65 mph.

Based on the available evidence, it appears the tire tracks (Photo 49) indicate that the pickup was traveling nearly parallel or at a slight angle to the road at the time of impact, but had its right-side tires approximately 18 inches past the paved shoulder. That offset and the marks left by the terminal head on the front bumper (Photo 50) indicate that the likely primary contact was with the left flange of the terminal face and was approximately one foot to the right of the center of the vehicle. The photo has been marked with a solid white arrow pointing to the deep indentation made by the traffic-side flange of the terminal's face. A dashed white arrow points to the lesser indentation made by the other flange.

The slight clockwise yawing that may have occurred with the initial impact would have been counteracted by the strong final forces on the left front corner of the vehicle (Photo 55). The net result was that the pickup essentially ended up parallel to the highway (Photo 57), but four feet farther away from the shoulder than it was at initial contact.

A set of illustrations the Task Force developed is presented that depicts its interpretation of one possible scenario of the likely sequence of events in this crash.

The potentially harmful occurrence in this case appears to be near occupant compartment penetration. The conditions of this crash were beyond what would be tested under NCHRP Report 350. The subject vehicle exceeds the mass of the 2000P test vehicle by approximately 10 percent, and the impact speed may have been slightly higher than the 62-mph speed used in crash testing.

Photos:

Photo 49

Photo 49 shows guardrail damage at post 1 for Case #1A009

Photo 50

Photo 50 shows vehicle damage for case #1A009

Photo 51

Photo 51 shows guardrail and vehicle damage for case #1A009

Photo 52

Photo 52 shows guardrail damage at terminal head for case #1A009

Photo 53

Photo 53 shows guardrail & vehicle damage for case #1A009

Photo 54

Photo 54 shows guardrail and vehicle damage for case #1A009

Photo 55

Photo 55 shows guardrail and vehicle damage for case #1A009

Photo 56

Photo 56 shows vehicle damage for case #1A009

Photo 57

Photo 57 shows vehicle and guardrail damage for case #1A009

Figure 37 – Police Report Crash diagram

Figure 37 shows police report diagram for case #1A009

Figure 38 – Illustration of one possible crash sequence

Figure 38 shows illustration of one possible crash sequence for case #1A009

Case: 5A009

Narrative:

This single-vehicle crash occurred at approximately 2:00 a.m. on an April morning. The weather was clear, the pavement was dry, and the roadway was tangent and level. The posted speed limit of the facility was 45 mph. The driver apparently fell asleep at the wheel and drifted off the right shoulder of the roadway.

The subject vehicle, a 2000 Chevrolet Express Single-unit Truck, left the roadway in a tracking manner (no evidence of skid marks or tire marks found at scene) and appears to have impacted a guardrail terminal head-on. The terminal post type is unknown due to the absence of on-site crash photos. Initial contact with the terminal appears to have been made with the front passenger-side bumper (Photo 58). The terminal head extruded an unknown amount of rail before the rail kinked and the terminal head was pushed away from the vehicle.

Based on the available evidence, it appears that several kinks formed after the initial impact and due to the mass of the vehicle (10,000-14,000 pounds), the vehicle continued down the rail with little, if any, yawing. The vehicle contacted one of the kinks in the front driver-side fender just in front of the wheel (Photo 59). The kinked rail penetrated the passenger compartment and continued through to the cargo box of the vehicle (Photo 60). At some point, the rail ruptured/separated at two separate splice joint locations (Photo 61).

The vehicle traveled approximately 100 feet after initial impact with the terminal, yawed slightly in a counter clockwise rotation, then rolled over onto its passenger side largely due to the slope behind the guardrail system.

The potentially harmful occurrence in this case appears to be occupant compartment penetration. The conditions of this crash were beyond what would be tested under NCHRP Report 350. Guardrail terminals are not designed for or tested with single-unit trucks, which can be much heavier than 4400-pound pickup trucks used in terminal crash tests.

Photos:

Photo 58

Photo 58 shows vehicle damage case #5A009

Photo 59

Photo 59 shows vehicle damage case #5A009

Photo 60

Photo 60 shows vehicle damage case #5A009

Photo 61

Photo 61 shows vehicle damage case #5A009

Figure 79 - Police Report Crash Diagram

Figure 79 shows police report diagram for case #5A009

Case #6A021

Narrative:

This single-vehicle crash occurred on a December afternoon on an 80-mph posted speed limit facility. The weather was cloudy, the pavement was dry, the roadway was straight and on a grade. For unknown reasons, the driver of the vehicle drifted to the left, departed the travel lane, and apparently struck a guardrail terminal head-on.

Information from the crash report indicates that the subject vehicle, a 2014 Jeep Grand Cherokee, struck the terminal at a relatively high rate of speed and made initial contact with the front center of the vehicle. The terminal post type is unknown due to the absence of on-site crash photos. Based on the available evidence, it appears the terminal extruded an unknown amount of rail before the terminal head was pushed away from the front of the vehicle. The police report crash diagram indicates the vehicle began to yaw counter-clockwise as the terminal head was being pushed away from the vehicle. At some point, it appears a kink formed in the rail. According to the police report, a section of the rail penetrated the occupant compartment through the rear passenger-side door.

The photos of the terminal head alone do not provide adequate information to assess the performance of the terminal. The photos appear to indicate both ends of the rail were cut in order for the terminal to be removed. Therefore, it cannot be determined how much rail was extruded through the terminal head.

The potentially harmful occurrence in this case appears to be occupant compartment penetration. The conditions of this crash were beyond what would be tested under NCHRP Report 350. The assumed impact speed of 75-80 mph was significantly higher than the 62-mph speed used in crash testing. This narrative is based on limited information from the crash report and post-crash terminal photos. No photos of the vehicle or crash scene were available.

Photos:

Photo 62

Photo 62 shows terminal damage for Case #6A021

Photo 63

Photo 63 shows terminal damage for Case #6A021

Photo 64

Photo 64 shows terminal damage for Case #6A021

Figure 40 - Police Report Crash Diagram

Figure 40 shows police report diagram for case #6A021

Performance Limitations: Installation Conditions

This section of the report covers placement, installation, and maintenance issues associated with extruding w-beam guardrail terminals. These issues can adversely affect the safety performance of w-beam guardrail terminals, but it is unknown to what extent, because terminals are not crash tested under less-than-ideal conditions. Designers encounter many constraints in the field (i.e., geographical challenges, environmental impacts, and restricted rights-of-way) that inhibit the ability to install these devices under standard crash tested (ideal) conditions. In many cases, it may be preferred to shield a hazard with a barrier installed under less-than-ideal conditions rather than leaving the hazard unshielded.

The Task Force identified placement, installation, and maintenance issues using: 1) reviews of individual crash cases, 2) FHWA's training effort to assist highway agencies with their design, installation, and maintenance practices for roadside safety hardware, and 3) the joint AASHTO-FHWA Task Force report on ET-Plus 4-inch Dimensions, which reviewed dimensions taken from ET-Plus 4-inch devices in the field.

In the review of the crash cases, the Task Force observed a number of placement, installation, and maintenance issues. These issues fall into three categories: 1) hardware installation/maintenance/repair, 2) grading (such as lack of relatively flat graded platform in advance of, and adjacent to, the terminal), and 3) placement (such as terminal located behind curb). Table 12 illustrates these issues with photos from individual crashes. For many of the issues, there is a brief statement about the potential effects on performance. However, it is not clear for these individual crash cases how they ultimately contributed to the outcome of the crash, which is why the performance statements in Table 12 should be viewed as potential effects.

Table 12- Installation Conditions Observed in Crash Cases

Issue

Crash Case Photos

Terminal Located Behind Curb

May affect the stability of the impacting vehicle.

Table 12 shows potentially adverse installation conditions observed in crash cases. Table 12 shows potentially adverse installation conditions observed in crash cases. Table 12 shows potentially adverse installation conditions observed in crash cases.

Lack of relatively flat graded platform in advance of, and adjacent to, terminal

Terminal can only anchor the guardrail for downstream impacts.

Table 12 shows potentially adverse installation conditions observed in crash cases.

Installation did not comply with the manufacturer's drawings

Bolted cable bracket used instead of tabbed bracket.

Terminal may not absorb energy in crash as designed.

Table 12 shows installation conditions for installation did not comply with manufacturer's drawings and terminal placement issues observed in crash cases.

Soil tubes protruding more than 4 inches above ground surface.

Vehicle undercarriage may snag on posts causing abrupt deceleration.

Table 12 shows installation conditions for installation did not comply with manufacturer's drawings and terminal placement issues observed in crash cases.

Installation did not comply with the manufacturer's drawings

Tangent terminal installed on flare.

Table 12 shows installation conditions for installation did not comply with manufacturer's drawings and terminal placement issues observed in crash cases. Table 12 shows installation conditions for installation did not comply with manufacturer's drawings and terminal placement issues observed in crash cases.

Flared terminal installed on tangent.

Table 12 shows installation conditions for installation did not comply with manufacturer's drawings and terminal placement issues observed in crash cases.

Terminal placement issues

Within, or just beyond, sloping gore areas.

Table 12 shows installation conditions for terminal placement issues observed in crash cases.

Terminal placement issues

Within curves

Energy absorbing terminals need a straight run of guardrail to travel on.

Table 12 shows installation conditions for terminal placement issues observed in crash cases.

Terminal placement issues

Where slopes behind the rail are relatively flat and free from obstacles (i.e., where a barrier may not be warranted)

Barrier may present a higher level of risk than the unshielded condition.

Table 12 shows installation conditions for terminal placement issues observed in crash cases. Table 12 shows installation conditions for terminal placement issues observed in crash cases.

Table 12 shows installation conditions for terminal placement issues observed in crash cases. Table 12 shows installation conditions for terminal placement issues observed in crash cases.

Other placement, installation, and maintenance issues for terminals exist beyond those highlighted through crash cases in Table 12. FHWA has documented these other issues in a technical brief as part of an FHWA memo (http://safety.fhwa.dot.gov/roadway_dept/policy_guide/road_hardware/policy_memo/memo052615/index.cfm) issued on May 26, 2015 and through the Agency's training effort titled "Roadside Safety Systems Inspection/Maintenance & Designers Mentoring Program" to assist highway agencies with their placement, installation, and maintenance practices of roadside safety hardware. This training has been delivered to ten States since 2010. Through the training visits to participating States, photographs of existing roadside safety hardware are taken in these States to document their design, installation, and maintenance practices.

Summary of Findings

A total of 1231 crash cases were received and 161 cases were selected for detailed review and analysis by the Task Force. Members of the Task Force identified six primary performance limitations of extruding w-beam guardrail terminals. These limitations are classified into two general categories: impact conditions and installation conditions. The impact conditions that the Task Force identified as performance limitations include side impacts, head-on/shallow-angle corner impacts, and head-on/shallow-angle high-energy impacts. The categories of installation conditions the Task Force identified as performance limitations include hardware installation/maintenance/repair, grading, and placement.

CONCLUSIONS AND RECOMMENDATIONS

This report documents a joint AASHTO and FHWA effort to examine the safety performance of extruding w-beam guardrail terminals with a focus on identifying their performance limitations. The ET-Plus w-beam guardrail terminal with a 4-inch wide feeder channel was the Task Force's primary focus, but the effort also included a review of other extruding w-beam guardrail terminals. The purpose of this effort was to determine whether there is any evidence of unique performance limitations of the ET-Plus 4-inch guardrail terminal and the degree to which any such performance limitations extend to other extruding w-beam guardrail terminals. The effort does not provide relative comparisons of the in-service safety performance of individual terminal types or an indication of the frequency of occurrence of the individual performance limitations because the collection of crash cases does not characterize a representative sample of terminals in service or a representative sample of terminals that were struck.

As background, the Task Force reviewed national safety statistics and data provided by States, which are presented in this report. Using FHWA's roadway departure definition and comparing fatalities on a national level, guardrail terminals represent a small percentage (0.2 percent) of total highway fatalities with respect to the most harmful event. These data include information on various w-beam guardrail terminals, including past designs that have no history of being crash tested under any prior performance criteria.

The Task Force determined that a detailed review of individual real-world crashes would provide the best opportunity to address the objectives of this effort. To identify potential performance limitations, the Task Force, with input from three independent expert reviewers, analyzed crash cases involving extruding w-beam guardrail terminals from 11 data sources. The crash case review process consisted of six primary components and included assessments conducted jointly by FHWA, State DOT representatives, and independent expert reviewers. Of the 1231 cases initially screened by FHWA, the Task Force and independent experts conducted a detailed analysis of 161 cases. These cases that comprised the focus of the analysis were viewed as the most likely to show potential performance limitations and represented a limited sample across five different guardrail terminal types. The data in this assessment were skewed toward severe crashes involving ET terminals; a limited sample of SKT and FLEAT cases were also captured.

Based on the analysis, the Task Force developed the following conclusions and recommendations to address the identified w-beam guardrail terminal performance limitations.

Conclusions

  1. Guardrail Terminal Crash Test Impact Conditions and Field-installed Conditions - The review of guardrail terminal performance based upon the limited number of crashes confirms what is acknowledged in National Cooperative Highway Research Program (NCHRP) Report 350[9] and the AASHTO Manual for Assessing Safety Hardware (MASH)[10] – there are real-world impact conditions that vary widely from the crash test matrices as related to vehicle type and sizes, first point of vehicle impact, vehicle non-tracking, and vehicle speed. Also, there are different installation and maintenance practices in place that can affect safety performance. Within the roadside safety community, it is recognized that even with the "best" practice of terminal design, with the wide variety of traffic and field conditions and applications, there will be crashes that exceed the performance expectations for the terminals. In addition, roadside features such as ditches, curbing, uneven terrain, and steep slopes in the vicinity of the terminal factor into the ability to mitigate the severity of the outcome of a guardrail terminal crash event. These terrain features can contribute to an increased likelihood of rollover during or after the impact event.

  2. Performance Limitations – Performance limitations are factors in a real-world crash environment that can contribute to the unsuccessful performance of a roadside safety hardware device. As indicated in MASH, guardrail terminals "are generally developed and tested for selected idealized situations that are intended to encompass a large majority, but not all, of the possible in-service collisions." Satisfactory performance can typically be expected for collision conditions similar to the test conditions. However, the performance of these devices is dictated by physical laws, vehicle stability, vehicle crashworthiness, and the site conditions of these real-world crashes. The more the crash conditions differ from the test conditions, the more likely it becomes that performance will be outside of the desirable limits.

    Through its analysis, the Task Force identified several performance limitations for all types of extruding w-beam guardrail terminals reviewed in this study. The limitations fall into two general categories: 1) impact conditions, and 2) installation conditions. For impact conditions, the primary performance limitations that were identified include: 1) side impacts, 2) head-on/shallow-angle corner impacts, and 3) head-on/shallow-angle high-energy impacts. For installation conditions, the performance limitations identified include: 1) hardware installation/maintenance/repair issues, 2) grading issues, and 3) placement that does not conform to accepted guidance and practice. These installation conditions can adversely affect the safety performance of these devices, but it is unknown to what extent, since terminals are crash tested under ideal, controlled conditions.

  3. NCHRP Report 350 Crash Test Criteria – NCHRP Report 350 crash test matrices do not specifically address the performance limitations the Task Force identified. It appears that side impacts, head-on/shallow-angle high-energy impacts, and head-on/shallow-angle corner impacts may lead to safety performance issues. However, the data analyzed did not allow for an assessment of how frequently these situations occur (i.e., they may be limited or they may appear on a regular basis) in the field. The shallow angle impact test condition is addressed in the MASH crash test criteria, but side impacts and front corner impacts are not specifically addressed in MASH. This points to the need to conduct in-service performance evaluations on roadside safety hardware including guardrail terminals; these evaluations are critical to determine whether crash-tested hardware have performance limitations that are not detected by the testing process and should be used to amend the crash test criteria in subsequent updates.

  4. Crash Testing of Extruding W-beam Guardrail Terminals – The Task Force considered additional crash testing of all existing NCHRP 350-compliant extruding w-beam guardrail terminals but concluded that such testing would not be informative because the performance limitations identified for these terminals fall outside of the NCHRP 350 testing matrices.

Recommendations

The Task Force developed the following recommendations:

  1. Fully Implement MASH Compliance for New Installations of Guardrail Terminals – This action is related to the roadside safety community setting a date by which new installations of guardrail terminals should be consistent with the MASH crash test criteria. MASH testing incorporates changes in the crash matrix details that will be more discerning for guardrail terminals. More specifically, MASH addresses impacts that occur at shallow angles, which is an important element in two of the performance limitations identified in this report. Each successive version of crash testing guidelines is meant to encourage manufacturers to advance the state of the practice and to develop safety devices that work with a changing vehicle fleet under a wider range of conditions. Because of the extensive development and testing required, it typically takes many years after roadside safety hardware guidelines are established for products meeting those guidelines to be widely available on the market. However, in the six years since MASH was published, there have not been a significant number of MASH-tested devices developed and brought to market. Therefore, in order to encourage the expanded development and installation of MASH-compliant devices, the Task Force supports the roadside safety design community to expeditiously transition to the MASH criteria for all new installations of guardrail terminals.

  2. Conduct In-Service Performance Evaluations of Guardrail Terminals – The Task Force recommends that comprehensive in-service performance evaluations of guardrail terminals be conducted at the national and State levels. As previously highlighted in this report, the Task Force's assessment did not involve a complete in-service evaluation and concentrated on a limited group of mostly higher severity crashes, specifically focused on crashes with the ET-Plus terminal. The findings of this report should be considered by the National Academies' National Research Council (NRC) committee that is conducting a project entitled "In-Service Performance of Energy-Absorbing W-beam Guardrail End Treatments." The intent of the NRC committee is to conduct exploratory work to determine what data are available, in sufficient quantity and quality, to allow for meaningful in-service evaluation studies of guardrail terminals.

  3. Expand Documentation of Guardrail Crashes – The Task Force recommends that AASHTO and FHWA encourage public agencies to thoroughly document guardrail crashes in order to allow for conducting more comprehensive in-service evaluations. Photographic evidence of an impacted guardrail and damaged vehicle(s) involved in a crash is extremely valuable and not typically captured. In addition, the Task Force recommends that AASHTO and FHWA request that the National Highway Traffic Safety Administration (NHTSA) thoroughly document guardrail crashes in its Crash Investigation Sampling System which is being phased in over the next two years as the replacement for the NASS CDS. Also, NCHRP project 17-43, "Long-Term Roadside Crash Data Collection Program," is providing an opportunity to improve data pertaining to roadside safety hardware that helps address this recommendation.

  4. Advance Noteworthy Safety Data and Roadside Hardware Inventory Practices – The Task Force recommends that the highway safety community and transportation agencies bring forward noteworthy practices for developing and maintaining roadside hardware inventory systems and also those that link crash data to the location and type of roadside safety devices. This linking is important and critical to obtain complete information for analyzing roadside crashes. FHWA has a noteworthy practices database established at the following web location where this information could be added in the future: (http://rspcb.safety.fhwa.dot.gov/noteworthy/default.aspx).

  5. Conduct Research on Vehicle Corner Impacts with Guardrail Terminals – The Task Force recommends that AASHTO and FHWA conduct research to evaluate the performance of vehicle front corner impacts with guardrail terminals to gain a better understanding of these crashes and the circumstances and conditions associated with them. Greater knowledge of this crash type could potentially be used to update future crash testing criteria. As summarized by this report, there were observed performance limitations with extruding w-beam guardrail terminals when the impact occurred at or near the vehicle corner in the headlight area.

  6. Conduct Research on Vehicle Side Impacts with Guardrail Terminals - The Task Force recommends that AASHTO and FHWA conduct research to evaluate the performance of vehicle side impacts with guardrail terminals to gain a better understanding of these crashes and the circumstances and conditions associated with them. Greater knowledge of this crash type could potentially be used to update future crash testing criteria. As summarized by this report, there were observed performance limitations with extruding w-beam guardrail terminals when the impact occurred on the side of the vehicle. The opportunity for research should be explored with NHTSA to review vehicle standards relative to the strength of the sides of passenger vehicles and to determine if vehicle side impacts into terminals and other fixed objects can be better addressed.

  7. Promote Proper Placement, Installation, and Maintenance Practices – The Task Force recommends that appropriate placement, installation, and maintenance practices be shared with the roadside safety community as was recently done through FHWA's May 26, 2015 memorandum. FHWA provides training and technical assistance on these practices, and the Task Force recommends that highway agencies take advantage of these resources. In addition, the Task Force recommends that AASHTO, through its Technical Committee on Roadside Safety, include additional content regarding proper placement, installation, and maintenance of guardrail terminals in the next edition of AASHTO's Roadside Design Guide.

  8. Crash Testing of Extruding W-beam Guardrail Terminals – The Task Force does not recommend additional crash testing of existing NCHRP 350-compliant extruding w-beam guardrail terminals for two reasons. First, the performance limitations identified for these terminals fall outside of the NCHRP 350 testing matrices, nor is it expected that NCHRP 350 tested devices function under all real-world conditions beyond what is present in the crash test scenarios. Second, as discussed in recommendation #1, the Task Force recommends that the roadside design community move to full implementation of MASH for all new installations of guardrail terminals which will help address an element of some of these performance limitations. Therefore, additional NCHRP 350 crash testing of existing guardrail terminals would be irrelevant since all crash testing since January 2011 has been required under the MASH criteria.


[1] TRB's National Cooperative Highway Research Report 350 – Recommended Procedures for the Safety Performance Evaluation of Highway Features,

[2] AASHTO's Manual for Assessing Safety Hardware, 2009.

[3] Roadside Design Guide, 4th Edition, 2011. American Association of State Highway and Transportation Officials.

[4] http://www.nhtsa.gov/FARS.

[5] Recommended Procedures for the Safety Performance Evaluation of Highway Features, NCHRP Report 350, 1993.

[6] 2013 FARS/NASS GES Coding and Validation Manual, Publication Number DOT HS 812 094, 2014.

[7] http://www.hsisinfo.org

[8] Fatal Injury (K): A fatal injury is any injury that results in death within 30 days after the motor vehicle crash in which the injury occurred. If the person did not die at the scene but died within 30 days of the motor vehicle crash in which the injury occurred, the injury classification should be changed from the attribute previously assigned to the attribute "Fatal Injury."

Suspected Serious Injury (A): A suspected serious injury is any injury other than fatal which results in one or more of the following: 1) Severe laceration resulting in exposure of underlying tissues/muscle/organs or resulting in significant loss of blood, 2) Broken or distorted extremity (arm or leg), 3) Crush injuries, 4) Suspected skull, chest, or abdominal injury other than bruises or minor lacerations, 5) Significant burns (second and third degree burns over 10% or more of the body), 6) Unconsciousness when taken from the crash scene, or 7) Paralysis.

Suspected Minor Injury (B): A minor injury is any injury that is evident at the scene of the crash, other than fatal or serious injuries. Examples include lump on the head, abrasions, bruises, minor lacerations (cuts on the skin surface with minimal bleeding and no exposure of deeper tissue/muscle).

Possible Injury (C): A possible injury is any injury reported or claimed which is not a fatal, suspected serious, or suspected minor injury. Examples include momentary loss of consciousness, claim of injury, limping, or complaint of pain, or nausea. Possible injuries are those which are reported by the person or are indicated by his/her behavior, but no wounds or injuries are readily evident.

No Apparent Injury (O): This is a property-damage only crash.No apparent injury is a situation where there is no reason to believe that the person received any bodily harm from the motor vehicle crash. There is no physical evidence of injury and the person does not report any change in normal function.

[9] TRB's National Cooperative Highway Research Report 350 – Recommended Procedures for the Safety Performance Evaluation of Highway Features,

[10] AASHTO's Manual for Assessing Safety Hardware, 2009.

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