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Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations

This summary report is an archived publication and may contain dated technical, contact, and link information
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Publication Number:  FHWA-HRT-16-071    Date:  August 2016
Publication Number: FHWA-HRT-16-071
Date: August 2016


FHWA Research and Technology Evaluation Program Summary Report Spring 2016


R&T Evaluation Summaries: Wave 1 Retrospective Evaluations

Adaptive Signal Control (Operations)

Program Description

Conventional traffic signal systems use preprogrammed daily signal timing schedules that do not automatically adjust to traffic conditions and can therefore contribute to traffic congestion and delay. Adaptive signal control (ASC) improves upon these systems by adjusting signal timing parameters that control the duration of red and green intervals to accommodate variability in demand using current traffic data. FHWA’s ASC research program, which was initiated in the early 1990s, supported both development and deployment of ASC in the United States. This research program, which spanned over 20 years, can be divided into three major phases:

The first two phases focused on technology development. FHWA funded two iterations of ASC technology development, managed pilot deployments, and developed informational materials to introduce the technology to traffic agencies. When development activities were complete, the program switched gears, focusing in the third phase on fostering ASC adoption by expanding outreach activities, developing guidance documents and materials, conducting training sessions, and providing technical assistance to agencies interested in pursuing the technology.

Purpose of the Evaluation

The purpose of the ASC program evaluation is to assess the effects of FHWA’s efforts related to developing ASCT and supporting the adoption of technology by State and local agencies.


The evaluation covered the three phases of FHWA research and outreach activities in two parts. The first part examined the entire ACST program through secondary research and interviews. The second part, which is ongoing, examines phase 3 through a survey of potential purchasers of ASCT.

The evaluation team reviewed research and documentation on the development, deployment, and impact of ASC to: identify stakeholders; understand the timing of relevant development activities, outputs, and short-term outcomes; and refine evaluation hypotheses. The documents reviewed included FHWA program material, websites of vendors and adopters, relevant research on ASC, and literature on technology diffusion models. Volpe conducted 19 interviews with ASC developers, vendors, local agencies, and FHWA program staff to provide context for the literature review. The team transcribed each interview and analyzed the notes to fill in gaps for the timeline analysis and to identify findings for each phase of FHWA research.

Initial Findings

Hypothesis 1: The FHWA R&T ASC activities accelerated the development of ASCTs.

Finding: FHWA had both a direct and indirect effect on ASC technology development (5)

In phase 1, FHWA directly funded the development and pilot testing of ASC algorithms through the RT-TRACS program. Of the four algorithms funded for development, three were pilot tested and two eventually came to market—Optimization Policies for Adaptive Control (OPAC) and Real Time Hierarchical Optimized Distributed Effective System (RHODES). Also, several of the signal control vendors and technology firms interviewed for this evaluation said that RT-TRACS encouraged them to begin or continue ASC research programs.

In phase 2, FHWA used lessons learned from RT-TRACS to develop ACS-Lite, a new algorithm that was less costly and complex for agencies to purchase and maintain. The contract firm developed the algorithm and four National Electrical Manufacturers Association (NEMA) signal control vendors partnered with FHWA to adapt their signal control equipment to run the technology. Two of the NEMA vendors went on to develop their own algorithms—one based on ACS-Lite. Outside these FHWA efforts, several vendors and technology firms developed or improved ASC products, often crediting RT-TRACS and ACS-Lite.

In phase 3, FHWA moved away from technology development to supporting ASCT in general. Eight additional ASCTs launched or came under development.

Hypothesis 2: FHWA R&T ASC activities accelerated the deployment of ASCTs.

Finding: FHWA development and outreach activities, particularly EDC, played a major role in overcoming initial reluctance in the market to adopt ASCT. (5)

During the first two phases, only a handful of agencies deployed technologies developed independently of FHWA: Sydney Coordinated Adaptive Traffic System (SCATS), Split Cycle Offset Optimization Technique (SCOOT), Los Angeles Adaptive Traffic Control System (LA ATCS), and Insync. Interviews, document review, and timeline analysis suggest that without FHWA’s programs, it is unlikely that many agencies would have been aware that the technologies were being developed and deployed in the United States at this time.(5) In phase 3, EDC shifted FHWA’s efforts from ASCT development to supporting the growth of the industry. The program reached State and local traffic agencies in 42 States, providing general information about ASCT through workshops, presentations, and meetings. The hallmark of the EDC effort was the development of the Model Systems Engineering Document for ASCT Systems, which provided guidance for State and local agencies on assessing and selecting ASCT systems. Interview responses suggest that EDC had a significant effect on encouraging agencies to adopt ASCT by providing the knowledge, training, and support needed to get the technology deployed. Since 2009, over 176 ASCT systems have been implemented, and many other agencies are considering the technology.

Hypothesis 3: The FHWA ASC activities improved mobility and reduced emissions.

Finding: Through the three phases of the FHWA R&T ASC program both FHWA-funded teams and FHWA-influenced technology firms have continued to develop ASCT systems, which improved travel time and reduced congestion in recent studies.(5)

Because there were few deployments of ASCT in the United States prior to 2009, the analysis of ASCT effectiveness is based on a relatively small number of performance evaluations in each phase (8 in phase 1, 18 in phase 2, and in phase 3). Therefore, the results speak primarily to the potential of the technology to impact congestion and travel time rather than its fully realized impact. Phase 1 studies showed mixed results in the ability of ACST to reduce travel time and delay. Phase 2 studies revealed improvement. Phase 3 studies show that the majority of ASCTs on the market—including all of those directly affected by FHWA—reduce travel time, delay, and congestion.

Geosynthetic Reinforced Soil Integrated Bridge System (Infrastructure R&D)

Program Description

Geosynthetic reinforced soil (GRS) technology consists of closely spaced layers of GRS and compacted granular fill material. The technology was first applied by the United States Forest Service (USFS) in the 1970s to build walls for roads in steep mountain terrain. Since then, FHWA has worked to evolve the technology into the Geosynthetic Reinforced Soil Integrated Bridge System (GRS-IBS), a fast, cost-effective method of bridge support that blends the roadway into the superstructure. The claimed advantages of GRS-IBS are that it is easy to design, uses low cost materials, can be built in variable weather conditions, and can easily be modified in the field.

The technology was selected for FHWA’s EDC initiative, which aims to accelerate the implementation of proven, market-ready technologies. To promote the technology to State departments of transportation (DOTs) and local transportation agencies, EDC conducted a total of 62 outreach events across the country between February 2011 and July 2015, including 24 State DOT workshops, 15 showcases of GRS-IBS projects, and numerous presentations at conferences and on webinars.(6) FHWA’s TFHRC disseminated several technical documents to assist transportation agencies in implementing GRS-IBS.

Purpose of the Evaluation

The purpose of the GRS-IBS program evaluation is to determine how effective FHWA’s outreach and technical assistance efforts were in increasing awareness, understanding, and deployment of GRS-IBS technologies by State and local transportation agencies. The evaluation also aims to determine the extent to which deployment of GRS-IBS technologies resulted in time or cost savings for infrastructure owners. The evaluation also examines the organizational supports and barriers to GRS-IBS deployment.


The evaluation team focused the evaluation of the GRS-IBS research program on outreach and deployment activities during the first two cycles of the FHWA EDC Program (2011–2014). The team reviewed FHWA documents and conducted 37 semistructured phone interviews. Relevant documents included FHWA materials, FHWA website statistics, and attendance at EDC events for GRS-IBS. Those interviewed included staff from TFHRC, the Resource Center, EDC, Federal Lands, and the Office of Infrastructure; local and State engineers, both from States that had attended outreach events and/or used GRS-IBS implementation materials, and those who had not. Design consultants, American Association of State Highway Transportation Officials (AASHTO) board members, and academic researchers were also interviewed. The evaluation is based primarily on these qualitative sources because of shortcomings in the quantitative data collected.

An additional study on GRS costs and a revision to the draft GRS-IBS evaluation report are forthcoming.

Initial Findings

Hypothesis 1: FHWA activities raised awareness and understanding of GRS-IBS technology and construction guidelines.

Finding: FHWA activities raised awareness and understanding of GRS-IBS technology and construction guidelines among the majority of stakeholders interviewed.

While 8 of the 11 State and local engineers interviewed said that they had not heard of GRS-IBS prior to attending an EDC event and many of the stakeholders interviewed spoke very positively about FHWA activities, this study cannot determine whether FHWA activities raised awareness nationwide.(6)

Hypothesis 2: FHWA activities accelerated the deployment of GRS-IBS technologies.

Finding: FHWA activities have supported local stakeholders and the pace of GRS-IBS bridge construction has increased.

But the degree to which the former contributed to the latter remains unclear. Stakeholders interviewed reported that FHWA materials and resources supported engineers implementing GRS-IBS. The data show that 34 GRS-IBS bridges were constructed in 23 different counties between 2011 and 2014 following exposure to FHWA outreach and technology transfer activities. This is an increase over the 11 GRS-IBS bridges constructed in 2 different counties between 2005 and 2010.(6)

Hypothesis 3: Accelerated deployment of GRS-IBS technologies resulting from FHWA activities reduced design and construction costs and time.

Finding: Preliminary analysis shows GRS-IBS technologies can reduce bridge construction costs and construction time, but conflicting evidence exists.

Research is underway to explain discrepancies. Most State DOT and local agency stakeholders who were involved in the construction of a bridge using GRS-IBS technology believed the technology helped to achieve cost and/or time savings in bridge construction. Some stakeholders said that the construction of a GRS-IBS bridge took as little as one-third to two-thirds of the time that a standard bridge took to build. Several stakeholders also reported cost savings up to 50 percent by using GRS.(6) However, some agencies reported higher costs. FHWA is sponsoring Volpe to investigate the source of these cost discrepancies. One possible explanation is that unfamiliarity with the technology leads some users to stray from GRS-IBS guidelines in ways that inflate costs.

Additional findings

Finding: Stakeholders reported hesitancy to embrace GRS-IBS technology both within FHWA and local agencies.

Some interviewees noted there was debate within FHWA as to whether GRS-IBS was ready for deployment. One FHWA engineer commented that “the implementation push got ahead of the ability to answer technical questions.”(6) Some engineers are also hesitant to depart from traditional methods of bridge construction. Interviewees noted that the “interim” status of GRS-IBS guidance led to uncertainty in the engineering field.

Finding: Initial support for GRS-IBS may be stronger at the county and municipal levels than at the State DOT level.

After multiple county and municipal agencies constructed GRS-IBS bridges in Pennsylvania, PennDOT adopted and approved the use of GRS-IBS design for low-volume local roads throughout the State.(6) Defiance County, OH, engineers are among the most aggressive adopters of GRS-IBS technologies.(6)

Gusset Plates (Infrastructure)

Program Description

The main span of the Interstate 35 West (I–35W) Bridge deck truss in Minneapolis, MN, collapsed on August 1, 2007, killing 13 people and injuring 145.(15) While investigating the incident, the National Transportation Safety Board’s (NTSB) turned to FHWA for technical expertise, focusing on the gusset plate construction of the deck truss. A gusset plate is a thick sheet of steel used to join structural components, such as connecting girders, to bracing or linking truss members. Before the I–35W Bridge collapse, bridge designers were given considerable discretion in designing gusset plates. Additionally, it was assumed that gusset plates should not have to be load rated unless there were changes in their condition, such as a section lost due to corrosion.

Within months of the collapse, NTSB issued its first recommendation—H-08-001—to FHWA, requiring that bridge owners conduct load capacity calculations to verify stress levels in all structural elements, including gusset plates.(16) In response to this recommendation, FHWA’s R&T conducted research and analysis on the failure modes of gusset plates and proposed recommendations for necessary gusset plate design and inspection standards through the NCHRP. The project culminated in NCHRP Web-Only Document 197, which was used to develop new AASHTO load and resistance factor design (LRFD) specifications for the design and rating of gusset plate bridges.(17)

Purpose of the Evaluation

This evaluation seeks to understand how FHWA’s investment in gusset plate research impacted the design and rating of gusset plate bridges. This report documents the process by which FHWA responded to NTSB’s recommendations—particularly Recommendation H-08-001—by conducting and disseminating key research to improve specifications for gusset plate design and load rating. The evaluation also examines how FHWA research contributed to the revision of AASHTO LRFD Bridge Design Specifications (BDS) and the Manual for Bridge Evaluation (MBE).


The evaluation team conducted interviews with key stakeholders and reviewed documents from FHWA, NTSB, and a selection of States. The Volpe team interviewed three NTSB staff members who worked on the I–35W Bridge investigation, two FHWA staff members who worked on key related efforts (the I–35W Bridge investigation, the Performance and Design of Steel Gusset Plate Connections project, and NCHRP Project 12-84), and four current and former members of the AASHTO Committee on Structural Steel Design.

The evaluation team also reviewed numerous documents and found six documents especially helpful: NTSB’s final report on the I–35W Bridge, NTSB’s first recommendations to FHWA, a set of correspondences between NTSB and FHWA, FHWA’s load rating recommendations, FHWA’s guidelines to bridge owners, and NCHRP’s gusset plate load rating specifications.

Initial Findings

Hypothesis 1: FHWA’s R&T activities led to the development, adoption, and application of improved specifications for the design and load rating of gusset plates.

Finding: FHWA’s technical expertise in bridge infrastructure and its prior history of working with NTSB was critical during the bridge investigation.(7)

FHWA ultimately provided the knowledge and expertise on gusset plate performance that led NTSB to conclude a gusset plate design error caused the collapse. Few truss bridges are being constructed, but many such bridges will exist in State inventories for a long time. FHWA’s input helped constructively refocus the conversation away from preventing gusset plate design errors to how States should maintain existing structures to prevent another collapse.

Finding: FHWA’s coordination with key stakeholders contributed to an accelerated timeline to closing NTSB recommendations.(7)

While Minnesota DOT and the engineering firm that designed and constructed the bridge were involved in discussions with NTSB, FHWA was the predominant party that participated in NTSB meetings about the problem and potential solutions. It became clear during the investigation phase that the gusset plate design problem had national implications, and FHWA was in a position to provide support on a far-reaching solution. FHWA’s close collaboration and coordination with NTSB was a major contributing factor to closing out NTSB’s recommendations.

Finding: FHWA’s commitment to bridge research and the decision to jointly fund the NCHRP effort accelerated the research timeline, resulting in expedient development of revised specifications for load rating and designing gusset plates.

Initial scoping efforts for what would eventually become NCHRP Project 12-84 began in May 2008. Within 2 months, FHWA and NCHRP reached an agreement to jointly fund the research. The project kicked off in October 2008, less than 1 year from initial scoping. The typical life of a NCHRP project concludes about six to seven years after funding is approved, and in the case of 12-84, it was determined that answers were needed much quicker for gusset plates than this typical time range. FHWA was able to hit the ground running without going through the development of a Request for Proposal and contractor selection that usually takes approximately 2 years. The quick initiation of the research project was integral to promptly updating AASHTO’s LRFD BDS and MBE

Hypothesis 2: FHWA’s R&T activities led to diffusion of new knowledge about the design and load rating of gusset plates.

Finding: FHWA’s active and ongoing engagement of transportation stakeholders expedited the delivery of new information regarding the design and load rating of gusset plates.

A review of correspondence between NTSB and FHWA concerning Recommendation H-08-001 shows that FHWA embarked on a series of internal and external outreach efforts related to gusset plate research.(7) FHWA, in conjunction with AASHTO, provided ongoing technical assistance and guidance to FHWA field offices and bridge owners about load rating and the evaluation of gusset plates on steel truss bridges. In 2009, FHWA published Load Rating Guidance and Examples for Bolted and Riveted Gusset Plates in Truss Bridges.(18) The agency also sponsored several national teleconferences and a conference to familiarize FHWA and State bridge engineers with using the FHWA guidance.

National Household Travel Survey (NHTS, Policy)

Program Description

National travel surveys have been conducted by the FHWA for over 45 years.The most recent versions, known as the National Household Travel Surveys (NHTS), were conducted in 2009 and 2001.(19,20) The surveys are the only data in the country that link individual personal travel behavior, household demographic and socioeconomic characteristics, vehicle ownership, and vehicle attributes.The NHTS data are used to monitor and track national travel behavior and also to provide information to States and metropolitan planning organizations (MPOs), where local data are oftentimes lacking.

Purpose of the Evaluation

The purpose of the evaluation is to understand the extent of use of FHWA’s NHTS data and the longer term impacts of their availability and use on policy, program, and regulatory decisions.


Volpe determined the range of users of NHTS data by reviewing FHWA documents and outreach efforts (including NHTS Web page usage statistics and by conducting interviews with lead users (academic, government, and consultants). The impact of FHWA’s NHTS data on decisionmaking relied on a review of Federal, State, MPO, and academic research products and interviews with NHTS staff and lead users. Measurement of the responsiveness of the NHTS program to user feedback was supported by document reviews and interviews. Lessons learned were also compiled through the interviews. Information gathered from documents and interviews was organized in a spreadsheet by key hypothesis, enabling a synthesis and comparison of information across sources.

Initial Findings

Hypothesis 1: NHTS activities produce data used by a range of users across multiple fields

Finding: Nearly half of the publications using the 2014 NHTS are in the transportation field with the share of non-transportation publications growing and website data access increasing.

An analysis of the 2014 NHTS Compendium of Uses document demonstrates that the NHTS are used across a range of fields.(21) While 46 percent of publications are primarily transportation focused, more than half of publications have a primary application in some other field, including energy (25 percent), survey methods or analysis (12 percent), environment (9 percent), and health (8 percent).(8) The evaluation team also found that NHTS publications cover a range of transportation topics. When Compendium publications are analyzed over time (2011 through 2014), the team found that the share of publications in nontransportation fields (e.g., health, environment, energy) grew significantly. Monthly website usage statistics for July 2013 through May 2015 indicate that use is robust with growth in some (but not all) metrics. For example, the number of monthly visits to the website increased from 5,118 to 8,443 over this time period.(8) The data also reveal a cyclical trend to usage, with spikes in the spring and fall.(8)

Hypothesis 2: NHTS data informs policy, projects, and regulatory decisionmaking

Finding: While it is difficult to trace the precise decision outputs of NHTS, the interviews suggest that NHTS informs policy and legislative decisions within transportation and other fields.

With respect to legislative uses, the evaluation team found NHTS data referenced in congressional reports, including “The Nation’s Highways, Bridges and Transit: Conditions and Performance Report” and in a series of reports produced by The National Surface Transportation Policy and Revenue Study Commission, established by Congress.(22) As an input to U.S. DOT Secretary Foxx’s “Beyond Traffic”, NHTS informs the national dialogue on the state of transportation.(23) Likewise the Safer People, Safer Streets: Pedestrian and Bicycle Safety Initiative by Secretary Foxx relies on NHTS data to provide an understanding of the use of biking and walking for daily travel.(24) NHTS data is also an input to the calculation of the model year Corporate Average Fuel Economy (CAFE) Standards.(25) In addition, NHTS is used in other fields including health, energy and the environment. For example, the CDC has incorporated NHTS data in its ten year agenda, Healthy People 2020, and most recently in the Surgeon General’s Call to Action to Promote Walking and Walkable Communities.(26,27) States and MPOs also utilize the data for a range of purposes, including to develop, calibrate, or validate their travel demand models. Interviewees indicated that these models are critical to transportation planning and also inform corridor level, interchange and transit projects, as well as air quality reports required by the Environmental Protection Agency (EPA) (e.g., in non-attainment areas).(8) However, tracing how and to what extent NHTS informs policy and legislative decisions is challenging since policy and legislative proceedings do not provide such information. One interviewee explained, “[NHTS] builds a mosaic of understanding and provides context, based on data; evidence can ripple through the system and have an effect. [NHTS] informs the conversation about important topics.”(8) Following such ripples through the system could serve as the basis for a future evaluation.

Hypothesis 3: The NHTS program is responsive to user feedback

Finding: NHTS reaches out to its user community through its website, direct contact, and formal events.

NHTS provides user support via its website and through direct contact with users who have questions and requests. NHTS also conducts a number of formal outreach activities, including Transportation Research Board (TRB) sessions, committee updates, workshops, and conferences. In 2011, NHTS organized the NHTS Task Force, which serves as a bridge between the NHTS team and the user community. Based on user feedback, NHTS has introduced more online tools (e.g., academy modules) and has changed its survey methodology.

Roadside Revegetation (Federal Lands)

Program Description

Twenty-eight percent of land in the United States is under Federal stewardship, including national parks, forests, wildlife refuges, and tribal and other Federal lands.(28) Native roadside revegetation involves establishing or reestablishing appropriate plant material on areas that road construction projects disturb. Its benefits include soil and slope stabilization, improved water quality, aesthetics, carbon sequestration, weed suppression, and enhanced wildlife habitat. Recognizing that sharing information about roadside revegetation processes and techniques is one way to advance the practice and achieve these benefits, FHWA’s Federal Lands Highway Division (FLH) teamed up with the USFS to develop an assessment and monitoring protocol for roadside revegetation. That protocol is documented in Roadside Revegetation: An Integrated Approach to Establishing Native Plants.(10)

Purpose of the Evaluation

The purpose of this evaluation is to determine how effective the guide and related materials (such as a website and training course featuring the guide) have been in achieving their stated goals, which are to:


The evaluation team reviewed the literature on revegetation, analyzed website usage and feedback from website users, and conducted an online survey with followup interviews. Literature was collected primarily from screening relevant websites and through library scans on keywords such as “roadside revegetation” and “native revegetation.” The review included manuals, policy documents, and guides from State agencies, the Bureau of Reclamation (BLM), and the National Park Service (NPS). FHWA’s Western Federal Lands (WFL) provided the project team with historical Web visitation statistics for all dates between January 1, 2010 and February 17, 2015, and recent examples of emails from end users. The emails offer insights about the perceived quality and effectiveness of the guide and website. From April 1, 2015, to approximately July 31, 2015, the project team administered an online survey to agencies that may have implemented practices from the Roadside Revegetation guide, receiving 39 responses from individuals in 21 States. Responding agencies included FHWA (23), USFS (7), NPS (5), and the U.S. Fish and Wildlife Service (2). Two State DOTs also responded. The survey asked questions regarding the level of awareness of Roadside Revegetation and its website, the extent to which stakeholders have adopted the practices described in the guide, and how effective the changed practices have been in achieving the establishment of native plants and other positive outcomes along roadsides.(29) The project team contacted 10 respondents for interviews based on responses to the online survey and conducted 4 interviews.

Initial Findings

Evaluation Area 1: The extent to which end users have adopted Roadside Revegetation guide practices

Finding: End users have adopted the Roadside Revegetation practices, using the guide as a reference tool to reinforce practices that agency policies already mandated.

The NPS, USFS, and some State DOTs hav0e policies aligned with roadside revegetation.(30,31) Additionally, visits to the nativevegetation.org have increased over time, with 44,621 total users from January 1, 2010 to February 17, 2015—approximately 24 per day. Over 7,000 of those users (nearly 16 percent) returned to the website more than once.(9) The data show that the most visited Web pages are in the technical guide itself. Multiple survey respondents noted that they primarily use Roadside Revegetation: An Integrated Approach to Establishing Native Plants as a general reference guide, while at the project site and when writing revegetation plans, designing monitoring protocols, developing scopes of work, and analyzing data.(9) The technical guide has enabled some practitioners to better define future conditions and end goals for project sites.

Evaluation Area 2: The extent to which Roadside Revegetation has improved the establishment of native plants and resulted in other positive outcomes

Finding: Survey respondents and interviewees believed Roadside Revegetation has generally improved erosion, sustainability and environmental stewardship, and visitor experience outcomes.

Interviewees and several survey respondents pointed out that the application of nonnative plants is probably less expensive than using native plants, but in the long term the maintenance of nonnative plants is more costly than native plants.(9) There is less indication that the technical guide has helped to improve safety or reduce maintenance costs. The majority of survey respondents neither agreed nor disagreed with the statement, “safety has been improved.”

Roundabouts (Safety)

Program Description

Roundabouts are circular intersections where approaching traffic yields to circulating traffic. Interest in roundabouts began internationally in the 1970s and 1980s for their ability to reduce speed and dangerous left-hand turns compared to traditional signalized intersections. In the mid-1990s, FHWA initiated research on roundabouts safety and design, leading to several papers and the publication of Roundabouts: An Informational Guide in 2000.(32) Later work led to higher quality performance data, refined roundabout design practice, and safety solutions for cyclists and pedestrians. Subsequent FHWA activities included the development and sharing of educational resources, training, technical assistance, and a partnership with NCHRP for the second edition of Roundabouts: An Informational Guide.(33)

Purpose of the Evaluation

The purpose of this evaluation is to assess the effects of FHWA’s investment in roundabout research on the availability and quality of roundabouts research, adoption of roundabouts in the United States, and the impacts of those roundabouts on the safety, operational, and environmental performance of the transportation system in the United States.


To benefit from active data collection efforts and reduce duplication, the evaluation team split the evaluation into two phases. The current report covers phase 1. The methodology and findings from the phase 2 will be covered in the final report.

The evaluation team employed a logic model to identify four evaluation areas with related primary hypotheses, secondary hypotheses, and performance measures. These are used to organize the initial findings.

The evaluation relies primarily on documentary evidence, supplemented by data analysis and interviews. The literature search included FHWA documents, relevant research on roundabouts, TRB Annual Meeting programs, Roundabouts List Serve archives, and literature on technology diffusion. To assess the influence of FHWA research and outreach on State DOTs, evaluators reviewed State-level materials, including Strategic Highway Safety Plans (SHSPs) and State highway design manuals, and State DOT websites.

The team used quantitative analysis—when available—to better understand the funding of roundabouts, the number of roundabouts, and the safety impacts of roundabouts. The evaluation team conducted interviews with FHWA staff and the TRB Roundabouts Committee chair to better understand the scope and extent of FHWA activities and to complement other analyses.

Initial Findings

The findings for the evaluation of roundabouts research highlight evidence from each of four evaluation areas.

Evaluation Area 1: The availability and reliability of roundabouts safety and performance data.

Finding: FHWA R&T research activities throughout the 1990s and up to the publication of the Informational Guide in 2000 led to a significant increase in the amount of published material on roundabouts in the United States.(32)

Initial FHWA contributions increased the availability of domestic roundabouts information by synthesizing international and the limited domestic safety and design research. The considerable impact of these contributions is evidenced by the number and breadth of citations to FHWA research and research influenced by FHWA. The interviews revealed that FHWA played an important role in accelerating consideration of roundabouts as a research topic and the development of domestically focused safety and performance studies.(11)

Evaluation Area 2: A change in awareness and knowledge of and attitudes towards roundabouts.

Finding: FHWA efforts have helped to shape State policies towards roundabouts and have changed the attitude of transportation professionals towards roundabouts as an intersection alternative.(11)

FHWA research, culminating in the 2000 Roundabouts: An Informational Guide, increased the availability of information on roundabouts in the United States. These products provided states and stakeholders with more information on how to utilize roundabouts as a safety countermeasure, and an FHWA endorsement of the technology. FHWA Safety R&D worked closely with the FHWA Office of Safety and the FHWA Resource Center to conduct sustained outreach, including making policy changes and recommendations within FHWA. This, in turn, shaped state policies towards roundabouts and resulted in changes of attitudes of transportation professionals towards the roundabout as an intersection alternative.

Evaluation Area 3: The adoption of roundabouts as a safety countermeasure

Finding: FHWA played an active role in accelerating the early adoption of roundabouts.

Through leadership and research and by meeting the needs of the earliest adopters, FHWA led to an increase in the total number of roundabouts. Funding provided under programs designed to increase safety (e.g., the Highway Safety Improvement Program (HSIP)), and traffic flow improvement and environmental benefits (e.g., the Congestion Mitigation and Air Quality Improvement Program (CMAQ)), provided continued support to the earliest and most confident adopters, while also providing confidence to later adopters.(36,37)

Evaluation Area 4: The safety, operational, environmental, and economic impacts of roundabouts

Finding: A review of the existing literature suggests there are significant emissions, operational flow, and safety benefits to roundabouts.

FHWA’s work to promote roundabouts in the United States has resulted in their increase in number. While considering the multidimensional impacts of all the roundabouts installed due to FHWA’s influence lies beyond the scope of this evaluation, the Volpe team reviewed the literature, which confirms that significant benefits accrue from installing modern roundabouts, including reduced emissions and improved operational flow. FHWA-influenced roundabout adoption has helped to reduce the number of crashes at U.S. intersections. The evaluation team calculated that the roundabouts installed in the United States between 1990 and 2014 averted between 38,000 and 53,000 injurious crashes, resulting in a societal cost savings upwards of $9 billion.(11) While FHWA cannot claim direct responsibility for this impact, its continued research and promotion of roundabouts has had a significant, positive impact on roadway safety in the United States.




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