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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-17-038     Date:  February 2018
Publication Number: FHWA-HRT-17-038
Date: February 2018


Completed Projects

TThis is a photo of two cars using a roundaboutThis is a photo of a two-lane road curving to the right around a hill. On the right side of the road is a yellow, diamond caution sign depicting upcoming curves in the road, which reads “35 MPH.”This is a photo of a three-light traffic signal mounted on a black horizontal bar. The traffic signal is red. A traffic camera is also mounted on the black bar to the left of the traffic signal.
This is a close-up photo of a yellow gusset plate on a bridge.This is a photo of a busy intersection in a city. The photo overlooks a crosswalk with white-striped lines. A line of busses is stopped in the crowded road. The sidewalks are crowded with people.

Sources (clockwise from top left): ©Michael Quinn, FHWA, ©Jeremy Brooks, ©Daniel Hoherd, FHWA.(8–12)

Adaptive Signal Control (Office of Operations R&D)

Program Description

In 1992, FHWA initiated research on ASC technology to better understand the potential of this technology to reduce traffic congestion and travel time delay in the U.S. ASC technologies adjust signal timing parameters in real time to accommodate variability in demand using current traffic data. FHWA’s ASC research program supported both development and deployment of ASC in the United States. FHWA funded two iterations of ASC development, managed pilot deployments, and developed informational materials on the technology. When development activities were complete, the program focused on fostering ASC adoption by expanding outreach activities, developing guidance materials, and supporting agencies through training and technical assistance.

Purpose of the Evaluation

The ASC evaluation assessed the effects of FHWA’s efforts related to developing ASC technologies and supporting the adoption of technology by State and local agencies. The evaluation team constructed three primary hypotheses about how the program was intended to work, centered on accelerated development of ASC, accelerated deployment of ASC, and improved mobility and emission outcomes because of ASC use.


Evaluators reviewed research and documentation on the development, deployment, and impact of ASC to pinpoint stakeholders; construct a timeline of development activities; and identify outputs, outcomes, and impacts achieved along this timeline. The evaluation team then conducted 19 interviews with ASC developers, vendors, local agencies, and FHWA program staff to refine and provide context to the information from the literature review. Evaluators designed and fielded an online survey with traffic agencies to connect what was learned from the in-depth interviews and timeline analysis to the direct experiences of the ASC market in considering and deploying the technologies.

Key Findings

Finding: Evidence from the ASC program shows that FHWA had both a direct and indirect effect on ASC development.

Early on, FHWA directly funded the development and pilot testing of three ASC algorithms for a real-time traffic adaptive signal control system (RT-TRACS). Two of the algorithms eventually came to market, while the research encouraged several other vendors to invest in ASC research. Subsequently, FHWA sought to improve upon the previous results by developing a new algorithm. The ACS Lite algorithm was developed by FHWA in partnership with signal vendors who agreed to adapt their equipment to run it. Two of the vendors then developed their own algorithms, one of which is based on ACS Lite. Outside FHWA, the cumulative effect of two development phases was noted to have a significant impact on the traffic signal control market. Several vendors and technology firms learned from the RT-TRACS and ACS Lite programs as they developed or improved ASC products. Since 2009, eight additional ASC technologies launched or started development.

Finding: The FHWA ASC activities helped bring the developer and adopter sides of the traffic signal control market together, accelerating the deployment of these ASC technologies.

Prior to 2009, pilot tests and demonstration sites represented the majority of ASC deployments; only a handful of agencies deployed non-FHWA technologies. Despite low deployment levels, the market began to pay attention; testing and outreach resulted in increased ASC awareness. Without FHWA’s programs, it is unlikely that many agencies would have been aware of domestic development and deployment. Starting in 2009, the Every Day Counts (EDC) program shifted FHWA’s efforts to outreach, which reached agencies in 42 states. FHWA provided training, guidance documents, and direct support. Study results show that EDC’s efforts are associated with increased ASC awareness.(13) Half of ASC adopters report using the EDC Systems Engineering Process and direct FHWA support through the complicated deployment process. Since 2009, over 176 cities have implemented ASC systems.

Finding: FHWA-funded teams and FHWA-influenced technology firms developed effective ASCs during the span of FHWA’s ASC program, showing the potential for improved mobility.

Throughout the FHWA program, the effectiveness of ASC technologies improved. Based on recent measures of effectiveness, ASCs can improve measures of travel time, delay, and number of stops in many situations, which can improve congestion on roadways. The relatively small number of evaluations, although promising, speak primarily to the potential of the technology to impact congestion and mobility, rather than its fully realized impact.


While focusing on technical issues, there should be consideration of and planning for the longer-term issues of market acceptance and deployment.

Early phases of the ASC program focused on developing technical ASC systems without fully understanding the needs and constraints of the market. FHWA should consider upfront market research to better understand both technology needs and barriers to adoption.

Strategies and processes for transferring a technology from research to the market should be considered when conducting initial research.

For FHWA-developed technologies to be widely used, vendors must have sufficient information on how to offer them to the market. Because different approaches may be appropriate at different times, upfront research with vendors and end-users can help programs better understand how best to meet market needs.

Communication about the technology itself and its related outreach program should be consistently shared throughout FHWA.

There were instances during EDC outreach when FHWA staff did not fully understand ASC and its applications, and this impacted the agencies’ ability to pursue ASC. FHWA should ensure that all staff responsible for a topic or product are aware of its applications and are able to communicate its uses and requirements to potential adopters.

Eco-Logical (Planning, Environment, and Realty/Second Strategic Highway Research Program)

Program Description

Developed by a team of representatives from FHWA and seven other Federal agencies, Eco-Logical articulates a vision for an infrastructure development process that endorses ecosystem-based mitigation by integrating plans and data across agency and disciplinary boundaries. Following Eco-Logical’s initial development as a guidebook, Second Strategic Highway Research Program (SHRP2) funds were used to create specific tools and techniques to implement Eco-Logical practices at State transportation departments and other planning agencies. FHWA has funded two rounds of pilot projects through the Eco-Logical Grant Program in 2007 and the 2013 SHRP2 Implementation Assistance Program (IAP).(14,15)

Purpose of the Evaluation

This evaluation assessed the effectiveness of FHWA R&T activities on the implementation of the Eco-Logical approach (i.e., ecosystem-based infrastructure planning and mitigation) to transportation project delivery by State transportation departments and metropolitan planning organization (MPO) recipients of FHWA Eco-Logical funding through the 2007 grants and 2013 SHRP2 IAP.


The evaluation team used five data collection and analysis methods to inform the evaluation: literature reviews of program materials from 2008 to 2015, participation in a program-sponsored peer exchange, stakeholder interviews in 2016, an analysis of Eco-Logical steps completed by funding recipients, and a qualitative coding analysis of stakeholder comments. Key evaluation questions considered FHWA’s dissemination of the approach to stakeholders, how grant recipients chose to incorporate the approach into their business practices, and how the Eco-Logical program and approach contributed to improved project delivery processes and environmental mitigation.

Key Findings

Finding: FHWA funding allowed agencies to pursue previously planned activities sooner, more comprehensively, and with broader stakeholder buy-in.

While several recipients indicated that they would have done their Eco-Logical-related work anyway, FHWA funding allowed them to expand the scope of work, dedicate more resources, and garner additional stakeholder buy-in. Some recipients noted that the success of their Eco-Logical work positioned them to apply and be selected for additional grant opportunities.

Finding: Agencies faced challenges working with their partners because of different missions, goals, and responsibilities; varying levels of support for Eco-Logical activities from federal agency staff at headquarters and regional levels; and staff turnover.

State transportation departments and MPOs sometimes found challenges with convincing local partners to consider impacts on a scale that extended beyond their jurisdictions as planning moved into project implementation. Recipients also noted differences between headquarters and regional level support, as regional staff may be more focused on legal requirements and the specific responsibilities of their jobs, rather than supporting grant projects.

Finding: Eco-Logical led to improved integrated planning between environment, transportation, and land use, and many recipients have incorporated Eco-Logical into their long-range transportation planning and project prioritization process.

Many recipients found value in cross-disciplinary collaboration early in planning through identifying shared goals, data, and plans. Some recipients stated that their Eco-Logical work informed how they prioritize projects. While these recipients did not always attribute project prioritization to impacts, early identification of issues allows agencies to avoid or minimize environmental impacts, which can improve environmental mitigation and yield time and cost savings later in project development. Despite these successes at the regional planning level, several MPOs remarked on their lack of authority when it came to ecosystem level decisions made at the local project-level scale.

Finding: Eco-Logical grant recipients reported few details on the impact of the program. Most comments were positive and without numerical evidence. Some grantees did not know what information to track or how to track the information.

The Eco-Logical projects typically spanned 2–3 years, and given the long timeframe of transportation and infrastructure projects, there was little reporting on impacts. Most comments related to impacts were positive and qualitative and tended to focus on the benefits of data sharing and analysis tools for prioritization. To do so, several recipients indicated they did not know what to track or how or they did not have the necessary resources. Some recipients noted that having examples of the time, cost, and environmental improvements that the Eco-Logical approach may afford would be useful in furthering adoption and implementation of the approach.


Recipient agencies would like FHWA to provide additional support in the form of peer exchanges, webinars, and case studies on Eco-Logical.

Topics of interest include the following: quantifying impacts, overcoming challenges, and receiving more information on applying the later steps of the approach. FHWA can facilitate peer learning on these topics.

FHWA should consider the continuity of awareness about Eco-Logical between headquarters and regional level staff within agencies and ensure consistent information is provided to stakeholders about the program and approach.

FHWA should explore additional opportunities to engage regional level staff in their program activities. FHWA should also examine how to engage local municipalities in implementing Eco-Logical on projects.

FHWA should consider using a set of consistent questions or tracking methods to evaluate the progress of recipient agencies from year to year and to ensure that overall progress on the Eco-Logical approach can be objectively measured long term.

FHWA’s interview questions changed over time and did not follow a set structure. This made it challenging to assess trends over time.

Activities to Date and Anticipated Schedule

The evaluation team delivered the draft evaluation report on September 29, 2016. Findings and recommendations presented here may change as a result of revisions for the final report.

Gusset Plates (Infrastructure)

Program Description

The main span of the Interstate 35 West (I–35W) bridge deck truss in Minneapolis, Minnesota, collapsed on August 1, 2007, killing 13 people and injuring 145.(16) While investigating the incident, the National Transportation Safety Board (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. Before the I–35W bridge collapse, bridge designers were given considerable discretion in designing gusset plates. In addition, it was assumed that gusset plates needed only to be load rated if there were changes in their condition, such as from corrosion.

Within months of the collapse, NTSB issued its first safety 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.(17) In response to this recommendation, FHWA R&T conducted research and analysis on the failure modes of gusset plates and proposed recommendations for gusset plate design and inspection standards through the NCHRP. The project culminated in NCHRP Web-Only Document 197, which was used to develop new American Association of State Highway and Transportation Officials (AASHTO) load and resistance factor design (LRFD) specifications for the design and rating of gusset plate bridges.(18)

Purpose of the Evaluation

This evaluation aimed to understand how FHWA’s investment in gusset plate research impacted the design and rating of gusset plate bridges. This report documents the process in which FHWA responded to NTSB’s recommendations—particularly Safety Recommendation H-08-001—by conducting and disseminating key research to improve specifications for gusset plate design and load rating. The evaluation also examined how FHWA research contributed to the revision of AASHTO LRFD Bridge Design Specifications (BDS) and the Manual for Bridge Evaluation (MBE).(18,19)


The evaluation team conducted interviews with key stakeholders and reviewed documents from FHWA, NTSB, and a selection of States. The evaluation team interviewed three NTSB staff members who worked on the I–35W bridge investigation, two FHWA staff members who worked on 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.(17,20)

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. (See references 19, 11, 20, and 21.)

Key Findings

Finding: FHWA’s technical expertise in bridge infrastructure and its prior history of working with NTSB was critical during the bridge investigation.(16)

FHWA ultimately provided the knowledge and expertise on gusset plate performance that led NTSB to conclude that 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.(16)

While the Minnesota transportation department 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 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 from initiation to conclusion.

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 began in October 2008, less than 1 year from initial scoping. A NCHRP project typically concludes about 6–7 years after funding is approved. It was determined that answers were needed quickly for Project 12-84, and FHWA was able to begin quickly without requesting proposals and selecting a contractor, which takes approximately 2 years. The quick initiation of the research project was integral to promptly updating AASHTO’s LRFD BDS and MBE.(18,19)

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 showed that FHWA embarked on a series of internal and external outreach efforts related to gusset plate research.(21) 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.(11) The agency also sponsored several national teleconferences and a conference to familiarize FHWA and State bridge engineers with using FHWA guidance.


FHWA should remain flexible on how its research funding is used.

In this case, there were approved projects that FHWA had originally intended to pursue regarding steel bridge research. Given the scale of the emergency and the immediate need for research and information, funds were redirected into the Gusset Plate Project. FHWA management showed flexibility with funding, and legislation at the time permitted such discretionary changes.

FHWA should consider how external input was gathered on this project and how FHWA might improve this approach for future high-profile research projects.

External input oversight from the NCHRP panel ensured the project stayed on track and avoided findings that were not useful. This external oversight is atypical in FHWA research programs, and this specific method of comingling resources raises questions about roles and responsibilities, particularly around contracting. Nevertheless, input (and, indeed, funding) from State transportation departments was appropriate and helpful.

National Household Travel Survey (Office of Policy)

Program Description

National travel surveys have been conducted by FHWA for more than 45 years. Now known as the National Household Travel Survey (NHTS), the most recent surveys were conducted in 2009 and 2001. 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. NHTS data are used to monitor and track national travel behavior and to provide information to States and MPOs, where local data are often lacking.

Purpose of the Evaluation

This evaluation aimed to understand the extent of use of FHWA’s NHTS data and the long-term impacts of their availability and use on policy, program, and regulatory decisions. In addition, the evaluation provided an assessment of NHTS responsiveness to its user community.


Evaluators determined the extent and range of NHTS data usage by reviewing FHWA documents and outreach efforts (including NHTS website usage statistics) and by conducting interviews with lead users (academic, government, and consultants). Assessing the impact of FHWA NHTS data on decisionmaking relied on a review of Federal, State, MPO, and academic research products and interviews with NHTS staff and lead users. Document reviews and interviews supported measuring the responsiveness of the NHTS program to user feedback. Through these interviews, the evaluation team compiled a list of lessons learned. The team organized information gathered from documents and interviews in a spreadsheet according to key hypotheses, enabling a synthesis and comparison of information across sources.

Key Findings

Finding: Nearly half of the publications using the 2014 NHTS are in the transportation field with the share of nontransportation 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.(22) 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).(23) The evaluation team also found that NHTS Compendium publications cover a range of transportation topics. When NHTS 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 indicated that use is robust with growth in some (but not all) measures. For example, the number of monthly visits to the website increased from 5,118 to 8,443 during this time period.(23) The data also revealed a cyclical trend to usage, with spikes in the spring and fall.(23)

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 2013 Status of the Nation’s Highways, Bridges, and Transit: Conditions and Performance.(24) As an input to U.S. Department of Transportation Secretary Foxx’s Beyond Traffic, NHTS guides the national dialogue on the state of transportation.(25) NHTS data are also an input to important models, including the model year Corporate Average Fuel Economy standards, which inform policy.(23) In addition, NHTS is used in other fields, including health, energy, and the environment. For example, the Centers for Disease Control and Prevention has incorporated NHTS data in its 10-year agenda, Healthy People 2020.(26) States and MPOs also use the data for a range of purposes, including to develop, calibrate, or validate their travel demand models, which are critical to transportation planning and also inform corridor level, interchange, and transit projects. However, tracing how and to what extent NHTS informs policy and legislative decisions is challenging because policy and legislative proceedings do not provide such information.

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 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 for the 2016–2017 NHTS.


Conduct NHTS on a more regular and frequent cycle.

The current 5- to 8-year cycle of surveys means that the data are considered “old” well before a new set of data are released. Moreover, the unpredictability of the survey schedule makes it difficult for users to depend on the data.

Institutionalize adequate funding, including staffing.

NHTS is not mandated, and so FHWA must obtain funding for each NHTS cycle, which has been a challenging process. In addition, the funding has not been adequate to meet the needs of the program. NHTS is currently run on a “limited” budget with minimal staffing.

Conduct more outreach, including with congressional policy staff.

With more outreach, NHTS could increase its value to the public and private sector. For example, outreach to congressional policy staff would likely result in more widespread use of the data. This outreach could also serve as a mechanism for better understanding the data needs of policy makers.

Roadside Revegetation (Federal Lands)

Program Description

Native roadside revegetation involves establishing or reestablishing appropriate plant material in areas that road construction projects disturb. Revegetation’s benefits include soil and slope stabilization, water quality improvement, aesthetic development, carbon sequestration, weed suppression, and wildlife habitat enhancement. In the United States, 28 percent of land is under Federal stewardship, including national parks, forests, wildlife refuges, and tribal and other Federal lands.(27) Recognizing that sharing information about roadside revegetation processes and techniques advances practice and achieves benefits, FHWA’s Federal Lands Highway Division partnered with the U.S. Forest Service to develop a protocol to assess and monitor roadside revegetation. The guide, Roadside Revegetation: An Integrated Approach to Establishing Native Plants, documents that protocol.(28)

Purpose of the Evaluation

This evaluation sought to determine how effective the guide and related materials (such as a website and training course featuring the guide) were in achieving their stated goals to accomplish the following:


The evaluation team reviewed the literature on revegetation, analyzed website usage and feedback from website users, and conducted an online survey with follow-up interviews. The review included manuals, policy documents, and guides from State agencies, the Bureau of Land Management, and the National Park Service (NPS). Web visitation statistics and end-user emails offered insights about the perceived quality and effectiveness of the guide and website. The survey asked questions on users’ awareness of Roadside Revegetation and its website, the extent to which stakeholders adopted the practices described in the guide, and the effectiveness of the changed practices 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.

Key Findings

Finding: End users have adopted the Roadside Revegetation practices,using the guide as a reference tool to reinforce practices that agency policies already mandated.(28)

The NPS, United States Forest Service, and some State transportation departments have policies aligned with roadside revegetation.(27) In addition, visits to www.nativerevegetation.org have increased over time, with 44,621 total users from January 1, 2010, to February 17, 2015—approximately 24 per day. More than 7,000 of those users (nearly 16 percent) returned to the website more than once.(27) 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.(28,27) The technical guide has enabled some practitioners to better define future conditions and end goals for project sites.

Finding: Survey respondents and interviewees believed Roadside Revegetation has generally improved erosion, sustainability, and environmental stewardship as well as visitor experience outcomes.(28) There is less indication that the technical guide has improved safety or reduced maintenance costs.

Survey results suggest that the majority of survey respondents agreed or strongly agreed that Roadside Revegetation has improved erosion outcomes, facilitated more sustainably designed roadways, improved visitor experiences, and enhanced environmental stewardship.(28) Interviewees and several survey respondents pointed out that the application of nonnative plants is probably less expensive than the use of native plants, but in the long-term, the maintenance of nonnative plants is more costly than the maintenance of native plants.(27) There is less evidence that the technical guide has improved safety or reduced maintenance costs. The majority of survey respondents neither agreed nor disagreed with the statement, “safety has been improved.”


Extend outreach to reach a wider audience, especially within FHWA Division Offices.

The project team found that Roadside Revegetation is still a useful reference, even for knowledgeable practitioners. Expanding the extent to which end users adopt its recommended practices would be beneficial.(28)

Support the enhancement of the community of practice at www.nativerevegetation.org.

Renewed attention to the community of practice on www.nativerevegetation.org could be a cost-effective way to broaden the sharing of knowledge to improve implementation outcomes.

Tailor future roadside revegetation training courses toward personnel who do not have natural resource backgrounds.

Training courses geared toward personnel who do not have natural resource backgrounds would be beneficial to highlight the nuances of installing and maintaining native plants.

Roundabout Research (Safety)

Program Description

International interest in the modern roundabout as a safety countermeasure began in the 1970s and 1980s. Compared to traditional signalized intersections or other circular intersections (e.g., rotaries and traffic circles), roundabouts can reduce crash severity. Starting in the mid-1990s, FHWA initiated domestic research and evaluation of roundabout safety and design, leading to several papers and the publication of Roundabouts: An Informational Guide in 2000.(30) FHWA continued work in this area, encompassing research related to performance data improvement and design state-of-the-practice. Later, FHWA activities across the FHWA Safety Discipline included development and sharing of educational resources, training, technical assistance, and a partnership with NCHRP for the 2010 Informational Guide update.(30)

Purpose of the Evaluation

This evaluation focused on FHWA’s contribution to roundabout research and technical guides, the use of that information in changing stakeholders’ awareness and attitudes, and the eventual adoption and impact of roundabouts as safety countermeasures.


The evaluation team used a mixed methods approach to more effectively investigate the outcomes and impacts of FHWA roundabout research. The evaluation team collected documents, analyzed data, and conducted semi-structured interviews. Data sources reviewed in the document and literature search included FHWA program documents, other relevant research, TRB Annual Meetings programs, Roundabouts Listserv archives, and literature on technology diffusion. To assess the influence of FHWA research and outreach to State transportation departments, Evaluators reviewed State-level materials including Strategic Highway Safety Plans (SHSPs), State Highway Design Manuals, and State transportation department websites. Where possible, evaluators used quantitative analysis to better understand the funding, quantity, and safety impacts of roundabouts.

Key Findings

Finding: Early and continued FHWA research increased the quality and availability of domestic roundabout-related safety and performance information.

FHWA laid the foundation for nationwide adoption of roundabouts by providing empirical evidence of the safety and operational benefits of roundabouts and aiding in the development of nationwide design standards for their implementation. Initial FHWA contributions increased the availability of domestic roundabouts information by synthesizing international and (limited) domestic safety and design research. These outputs in turn clarified and focused the research questions for the domestic research and design standards communities (with whom FHWA actively partnered and supported). FHWA targeted materials to a variety of audiences across the technology adoption lifecycle, including the research community, State transportation departments, local agencies, and the public. Interviews yielded information about the timing and effect of research and other activities on the research community and showed that FHWA played a key role in accelerating consideration of roundabouts as a research topic and the development of domestically-focused safety and performance studies.

Finding: FHWA roundabout research increased awareness and changed attitudes in the transportation community toward the roundabout as a safety countermeasure.

FHWA research, culminating in the 2000 Roundabouts Informational Guide, increased the availability of information on roundabouts in the United States.(30,31) These products provided interested states and stakeholders with more information on how to use 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, such as the inclusion of Roundabouts in EDC and Proven Safety Countermeasures. This, in turn, shaped State policies regarding roundabouts and resulted in changes of attitudes of transportation professionals toward roundabouts as an intersection alternative.

Finding: FHWA contributed to an increase in roundabouts built in the United States.

FHWA increased the total number of roundabouts through continued support, research, promotion, and funding. Funding for programs designed to increase safety (Highway Safety Improvement Program (HSIP)) and improve traffic flows and environmental benefits (Congestion Mitigation and Air Quality) provided continued support to the earliest adopters, while imparting a confidence boost to late adopters. However, despite increased construction and acceptance of roundabouts, the rate of adoption of roundabouts in the United States appears to have slowed and lags behind leading international adopters. Negative public attitudes and perceived high costs remain barriers.(30)

Finding: FHWA research and promotion of roundabouts contributed to a reduction in injury crashes and societal costs.

A simplified calculation of the safety effect of the approximately 2,400 roundabouts installed in the United States between 1990 and 2014 finds they averted between 38,000 and 53,000 injury crashes, resulting in a societal cost savings of over $9 billion during that period.(31) While FHWA cannot claim exclusive credit for this benefit, its continued research and promotion of roundabouts has been very positive for roadway safety in the United States.


Begin investing in data collection on research diffusion and technology adoption during the early years of technology implementation.

A lack of data hinders attempts to evaluate the adoption and impact of new transportation technologies. FHWA could strategically select a subset of technologies for systematic collection of adoption data. FHWA should also systematize internal metrics related to research investment and outreach.

Build cooperation across FHWA safety disciplines and the broader stakeholder community.

FHWA’s successful internal coordination across the safety discipline led to a highly visible and unified message to stakeholders. Documenting and replicating the coordination mechanisms, strategies, and activities that made this process successful could provide organization-wide benefits.

Conduct additional research to understand roundabout costs and identify and promote information and strategies on reducing those costs.

Although the U.S. increase in number of roundabouts has been significant, their adoption still lags behind other countries. Perceptions and uncertainty about the cost of roundabouts remain barriers.



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