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Federal Highway Administration > Publications > Public Roads > Vol. 57· No. 1 > The Highway Perspective of Side Impacts

Summer 1993
Vol. 57· No. 1

The Highway Perspective of Side Impacts

by Jerry A. Reagan

This paper incorporates opening remarks presented at the Society for Automotive Engineers International Congress and Exposition held in Detroit, Michigan, on March 1-5, 1993. The author was a cochairperson on a session on side impact collisions.

The National Highway Traffic Safety Administration (NHTSA) seeks to improve highway safety by improving the crashworthiness of motor vehicles. In recent years NHTSA and the automobile industry have been involved in studying side-impact issues. These studies have focused on vehicle-to-vehicle side impacts and the injuries associated with such collisions.

The Federal Highway Administration (FHWA) seeks to improve highway safety through the design, construction, and maintenance of safer highways. For the past decade, FHWA has been studying the side-impact issues from a roadside safety hardware perspective. We are currently focused on side impacts into narrow objects such as trees, utility poles, sign and light supports, and guardrail terminals.

While there has been some exchange of ideas within the agencies at the working level, both agencies and the automobile industry have largely pursued their respective interest independently. Efforts to work together have been hampered because of the limited information available on side impacts into narrow objects, the lack of a common scientific basis for sharing information, and a lack of understanding of highway design practices. To overcome these problems, FHWA, through the Federal Outdoor Impact Laboratory (FOIL), conducted a series of side-impact tests into narrow objects. The results of these tests are available in four reports. (1,2,3,4) The data provide valuable information on side impacts into narrow objects, including the performance of small cars when impacting existing roadside safety hardware. The number of fatalities and the severity of injuries mandate that the agencies and industry work closely together to design automobile and roadside safety hardware as a system.

A quick glance at some statistical data will show that each agency's perspective is important. Data on fatalities are from the Fatal Accident Reporting System (FARS) and all other data are from the National Accident Sampling System (NASS) Continuous Sampling System (CSS). There are also some differences in the way FARS and NASS data are coded. For example, the NASS CSS does not contain most harmful event data. However, the general trends are accurate.

Table 1 - Fatalities and injuries by most harmful event (1985) (5)

Most Harmful EventFARS (Fatalities)NASS (Injuries)
FrequencyPercentFrequencyPercent
Vehicle-to-Vehicle
17,495401,721,00051
Fixed Object
9,23921503,00015
Pedestrian/Cyclist
7,48117114,0003
Overturn
6,69815186,0006
Other/Unknown
2,9127839,00025
Total
43,8251003,363,000100

Table 1 shows the seriousness of fixed-object and overturn most harmful events (5). Both fixed-object and overturn (as well as pedestrian/cyclists) account for a greater percentage of total fatalities than they do of total injuries. Fixed objects account for 21 percent of all fatalities and 15 percent of all injuries. Overturns account for 15 percent of all fatalities and 6 percent of all injuries. By comparison vehicle-to-vehicle collisions account for a smaller percent of total fatalities (40 percent) than they do of total injuries (51 percent).

Table 2 - Roadside fatalities - most harmful event is outside the shoulder (1985) (5)

Harmful EventMost Harmful EventPercent
Fixed Object
8,10756
Overturn
4,82033
Other/Unknown
1,50811
Total
14,435100

Table 2 lists all of the fatalities of Table 1 in which the first harmful event is outside the highway shoulder. (5) This is the roadside safety problem. Note that 72 percent of all overturns (4,820 out of 6,698) occur on the roadside. Fixed-object collisions constitute 56 percent of the roadside fatalities. This paper does not discuss overturns (rollovers), but they too are a serious problem both for NHTSA (crashworthiness) and FHWA (design).

Table 3 - Occupants involved in single or multiple vehicle accidents where the most harmful event was a fixed roadside object by region of impact (2)

Most Harmful Event1980-1985 FARS1982-1985 NASS
FrequencyPercentFrequencyPercent
Front
5,70165603,00066
Side
2,24165226,00025
Rear
168227,0003
Other
685858,0006
Total
8,795100914,000100

Roadside hazard, fixed-object collisions can be further broken down by the region of impact where the vehicle struck the fixed object. Table 3 shows that in both the FARS and the NASS data, the roadside hazard, fixed-object, side-impact category represents 25 percent of the total fixed-object roadside safety problem.

Table 4 - Occupants involved in single-vehicle, fixed-object, side-impacts by vehicle type (2)

Most Harmful Event1980-1985 FARS1982-1985 NASS
FrequencyPercentFrequencyPercent
Passenger
1,64779168,00079
Utility
2621226,00012
Motorcycle
15184,7002
Other
36113,0007
Total
2,096100211,700100

The roadside hazard, fixed-object, side-impact problem is broken down by vehicle type in Table 4. Table 5 shows that most passenger car crashes involve narrow objects such as trees, utility poles, sign and light supports, and guardrail terminals.

Table 5 - Type of fixed object struck in single passenger vehicle, side impact, fixed object accidents (5)

Object Struck1980-1985 FARS1982-1985 NASS
FrequencyPercentFrequencyPercent
Narrow
1,31480100,00059
Broad
1891130,0002
Other
144938,00023
Total
1,647100168,000100

In summary, approximately 160,000 people are involved in accidents where the side of the passenger car impacts a fixed roadside object such as a tree, utility pole, light support, etc. More than 1,600 occupants-- about one in 100--are killed. The annual cost to society is $3 billion each year.

Given the magnitude of the problem, serious thought must be given to reducing this tragedy. NHTSA, FHWA, and the automobile industry must recognize that the vehicle and the roadway cannot be treated separately. The crashworthiness of cars and the design of roadside safety hardware represent a system. Treatment of the vehicle and the roadway as a system means that many of the concepts that have been used in the past must be re-examined. It may be that the current notions favoring redirection when cars impact guardrails and roadside safety hardware that breaks away on impact need to be re-examined. It may also mean that the current dynamic side impact test standard, Federal Motor Safety Standard (FMVSS) 214, should include a car-to-fixed-object test as well as the current car-to-car test.

Additional work on side impacts into fixed objects is planned by FHWA. It is anticipated that much of the work will be coordinated with NHTSA with three ideas in mind. First, FHWA, NHTSA, and the automobile industry need to agree on a standard set of analytic tools so that data can be shared and understood. Secondly, there needs to be a standard vehicle adopted by FHWA, NHTSA, and the automobile industry that can be used for the design of roadside appurtenances under side-impact conditions. Such a vehicle should represent the best thinking on how future vehicles will be constructed. Third, the design of roadside safety appurtenances may require changes in both existing hardware and automobile side structure.

It is anticipated that this additional work will build on two joint FHWA/NHTSA initiatives that are now underway. FHWA/NHTSA have signed an interagency agreement with the Department of Energy to have the Lawrence Livermore National Laboratory (LLNL) adapt the non-linear finite element code DYNA3D to simulate crash impacts. LLNL are developers of the DYNA3D code. In addition, FHWA and NHTSA are jointly funding the National Crash Analysis Center (NCAC) located on the George Washington University Virginia Campus. The NCAC maintains all FHWA and NHTSA crash films and uses these films for crash analyses, including side impacts. Finally, the side-impact crash tests supporting this program will be conducted at FOIL. FOIL is located at the Turner-Fairbank Highway Research Center in McLean, Virginia, and has a unique capability to conduct side-impact tests into narrow objects.

References

(1) J.A. Finch, J.A. Hansen, M.W. Hargrave and D.R. Stout. Full-scale Side Impact Testing, Publication No. FHWA RD-89-157, Federal Highway Administration, Washington, DC, February 1989.

(2) L.A. Troxel, M.H. Ray, and J.F. Carney III. Accident Data Analysis of Side-Impact Fixed Object Collision, Publication No. FHWA-RD-91-122, Federal Highway Administration, Washington, DC, May 1993.

(3) M.H. Ray and J.F. Carney III. Side Impact Test and Evaluation Procedures for Roadside Structures Crash Tests, Publication No. FHWA-RD-92-062, Federal Highway Administration, Washington, DC, April 1993.

(4) M.H. Ray and J.F. Carney III. Side Impact Crash Testing of Roadside Structures, Publication No. FHWA-RD-92-079, Federal Highway Administration, Washington, DC, April 1993.

(5) J.G. Viner. "Harmful Events in Crashes," Accident Analysis and Prevention, Volume 25, Number 2, April 1993, pp. 139-45.

Jerry A. Reagan is chief of the Design Concepts Research Division, Office of the Associate Administrator for Research and Development, Federal Highway Administration (FHWA) at the Turner-Fairbank Highway Research Center (TFHRC) in McLean, Va. Prior to that assignment, he served as the chief of the Safety Traffic Implementation Division. He has had a variety of experiences with FHWA, beginning in 1967 as a materials engineer. Later he was assigned to Region 15 as a soils and foundation engineer. In 1973, he transferred to the Office of Environmental Policy at FHWA headquarters where he worked for 10 years. Then he moved to TFHRC as the state programs officer of the National Institute of Highways where he was responsible for the NHI short course.

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