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Suggested Citation:"Summary." National Academies of Sciences, Engineering, and Medicine. 2019. Pedestrian Safety Relative to Traffic-Speed Management. Washington, DC: The National Academies Press. doi: 10.17226/25618.
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Suggested Citation:"Summary." National Academies of Sciences, Engineering, and Medicine. 2019. Pedestrian Safety Relative to Traffic-Speed Management. Washington, DC: The National Academies Press. doi: 10.17226/25618.
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Suggested Citation:"Summary." National Academies of Sciences, Engineering, and Medicine. 2019. Pedestrian Safety Relative to Traffic-Speed Management. Washington, DC: The National Academies Press. doi: 10.17226/25618.
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1 This synthesis aims to document what is known about strategies and countermeasures to address pedestrian safety via traffic-speed management in urban environments. This topic is ripe for exploration, given the thousands of pedestrians who are killed and hundreds of thousands who are injured in traffic collisions annually. Though there are often multiple factors contributing to a pedestrian crash, a consistent factor contributing to pedestrian injury severity is vehicle speed. Research has found unequivocally that higher speeds lead to higher injury severity (Rosén and Sander 2009; Tefft 2013), and many agencies are seeking tools and strategies to retrofit or redesign roadways—particularly those with destinations that people need to access on foot—for speeds more aligned with pedestrian-safety goals. These high numbers have spurred many jurisdictions to consider a different approach to addressing pedestrian safety, represented frequently by the Vision Zero movement, which aims to eliminate traffic fatalities and serious injuries within a defined timeframe. Vision Zero incorporates the principles of the Safe System approach employed in many countries, which recognizes a role for multiple parties in improving safety, rather than primarily and often exclusively holding the people involved in the collision responsible. A key tenet of the Safe System/Vision Zero approach is that the human body can with- stand only a certain amount of impact before life-altering injuries occur. Because the kinetic energy behind the impact is directly influenced by vehicle speed, managing speed is a critical element of any Vision Zero effort. This view of speed—as something to be managed in order to promote safety, rather than primarily to alleviate congestion—represents the begin- ning of a paradigm shift for many agencies around the United States and internationally. Yet most U.S. cities still find themselves with roadways and contexts that promote higher speeds, whether through the speed limits themselves, the lack of environmental cues to slow down sufficiently for pedestrian safety, or the lack of speed-enforcement options. It is in this context that the need for this synthesis emerged. Agencies are seeking effective practices for managing speed to promote pedestrian safety and desire to know what others in the field have learned through their own work and to explore the latest research findings on the topic. To meet this need, this synthesis aims to compile existing information and accomplish the following two objectives: 1. Identify proven strategies and effective practices related to improving pedestrian safety via traffic-speed management and 2. Clarify gaps in current knowledge in order to better understand how to design research projects to fill those gaps in the future. This study was carried out using the following two methods: 1. a multipronged literature review to document the impacts of speed on pedestrian safety, various countermeasures’ S U M M A R Y Pedestrian Safety Relative to Traffic-Speed Management

2 Pedestrian Safety Relative to Traffic-Speed Management effectiveness with regard to slowing speed, and alternatives to setting speeds, and 2. inter- views with practitioners to learn more about their speed-management efforts and results. The project focused on interviews with local and regional jurisdictions rather than state depart- ments of transportation (DOTs) because the topic panel sought an emphasis on Vision Zero programs, given their dedicated efforts to address pedestrian safety, and these programs tend to occur at the city level. However, the interviews explored the cities’ relationships with state DOTs and offered insights into ways that local jurisdictions can work with the state to create safer conditions for pedestrians with regard to traffic-speed management. The literature review indicated that few studies of countermeasures specifically look at pedestrian safety as an outcome of efforts to slow speed. However, many studies look at the effectiveness of countermeasures with regard to slowing speeds in general, and particularly on local roads. Therefore, the literature review focused on the latter category of studies. The most effective of these are countermeasures with vertical deflection, such as speed humps and speed bumps, which force the driver to slow down to avoid discomfort or car damage. Countermeasures that use horizontal deflection, such as chicanes and mini traffic circles, also have shown some effectiveness by forcing the driver to slow to move around a physical object in the roadway. Within each of these categories, some countermeasures are more effective than others are, and both categories have limitations on where they can be used, being desig- nated generally for lower-speed roads except in certain circumstances. Thus, while these are important countermeasures for some circumstances, particularly where very low speeds are desired (such as in school zones), they are not as appropriate for and are often prohibited from use on the higher-speed roads where pedestrian injury severity is likely to be greatest. The countermeasures that are effective for constraining speed on higher-speed roads tend to involve either roadway redesign or speed enforcement. The literature review found con- sistent evidence that automated speed enforcement (ASE) in particular can be an important part of an agency’s work to control speeding. ASE also has the benefit of being resource- efficient, by not requiring active patrols and allowing officers to focus on other issues, and will not discriminate based on race, ethnicity, or any other factor—it simply tickets those going above the speed limit. That said, care still needs to be taken when ASE is implemented in communities to ensure that certain parts of the community are not disproportionately affected by ASE without commensurate efforts to address roadway designs that have left them with roads where speeding is more likely. The interviews reflected the practices of various Vision Zero cities and cities otherwise actively pursuing traffic-speed management to improve pedestrian safety that have either proven or promising results to share. During each hour-long interview, agency representa- tives described the various efforts their agencies are making to reduce traffic speed and improve pedestrian safety. These efforts included engineering and design, operations, edu- cation and outreach, and policies and programs. The efforts varied by jurisdiction and were tailored for the appropriate context. For example, in dense San Francisco, curb extensions have been a popular and effective traffic-calming measure. In Seattle, street reconfigurations (road diets) have proven successful for lowering speeds and improving safety. However, neither of those options have been as effective or politically feasible in the City of Los Angeles; instead, the Los Angeles staff are experimenting and innovating with technology that can alert police in real time about areas with speeding drivers without violating the state’s privacy laws (which currently prohibit ASE). The interviewees also discussed barriers to addressing traffic speed, such as being required to use the 85th percentile method that allows higher speeds to dominate in areas and on roadways many cities would like to see operate at lower speeds. Agency representatives also discussed lessons learned from unpopular speed-reduction efforts, emphasizing the need

Summary 3 for extensive community outreach before making big changes even when the data clearly indicate a speeding problem and safety issues. In many ways, the interviewees confirmed the dominance of a culture of speed created from and reinforced by prioritizing mobility over safety for decades in the United States. This culture is difficult to change, but addressing it will be necessary if cities are to reach their Vision Zero goals. The interviewees were optimistic about their efforts, however. They related stories of strong partnerships with community organizations and advocacy groups working together to achieve a safer city and celebrated successful speed-reduction efforts and promising strategies for future work. Their stories may encourage other practitioners and provide inspiration for future speed-reduction strategies and countermeasures in this area. The report concludes with a review of key findings and identifies gaps in the research and practice in need of future study. Overall, this synthesis covers a subject area that would benefit from additional research. Although there are many countermeasures known to be effective at reducing speed, few have been studied specifically with regard to pedestrian safety. This may be due to the focus of the studies (i.e., that the outcomes are generally speed related, with an overarching assumption that slower speeds improve safety). The lack of outright connection may also be due to the nature of where countermeasures are installed; lower-speed roads are less likely to have high numbers of pedestrian crashes to begin with, so studies of countermeasures may lack sufficient numbers from which to draw conclusions unless carefully designed to cover a sufficient number of sites. Countermeasures applicable to higher-speed roadways have demonstrated more success specifically with regard to pedestrian safety, but could use additional study in this area. There is also a clear need for additional countermeasures and strategies for these contexts in areas where ASE, one of the most effective countermeasures for higher-speed roadways, is prohibited. In general, studies investigating the effectiveness of promising-but-unproven countermeasures could provide needed understanding and potentially augment the toolbox for practitioners seeking to address pedestrian safety via traffic-speed management. Finally, this synthesis revealed a need for greater clarity about the speed-limit-setting pro- cess, as well as for greater collaboration between local and state agencies when state roads run through urban areas. In particular, there seems to be a need for a framework that will foster collaboration between local and state staff on safety initiatives such as achieving flexibility in roadway design, changing laws or regulations that govern speed-limit setting, and finding a balance between local safety needs and regional mobility needs. Ideally, this framework will support both local and state agencies attempting to address safety issues and reach larger goals as articulated through movements like Vision Zero and Toward Zero Deaths.

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Measures that are effective at reducing speed, such as speed humps and mini traffic circles, are sometimes used in low-speed areas such as school zones. But they are often not recommended or allowed (via local policy) on the higher-speed streets typically associated with the highest injury severity for pedestrians.

For those higher-speed streets, redesigning them to communicate lower speed, such as through a roadway-reconfiguration effort, can effectively accomplish the goal of lowering speed. In the absence of street redesign, however, another effective current solution is enforcement, and particularly automated speed enforcement (ASE) that frees police to focus on other issues and that is free from implicit or explicit bias. It is important to carefully consider community context when selecting locations to employ ASE, to avoid disproportionately burdening any historically disadvantaged communities that surround the typically high-speed streets that need to be addressed.

The TRB National Cooperative Highway Research Program's NCHRP Synthesis 535: Pedestrian Safety Relative to Traffic-Speed Management aims to document what is known about strategies and countermeasures to address pedestrian safety via traffic-speed management in urban environments. For example, the City of San Francisco regularly uses curb extensions as traffic-calming devices on its streets. However, the political and land use context of each city heavily influences the types of treatments that are considered feasible for each city. Thus, the City of Los Angeles has had to find alternatives to both ASE and road diets, the latter of which have been the subject of intense public backlash in some cases.

These realities—that speed management can be fraught with difficulty—have spurred creative thinking about how to work within contextual confines, resulting in some particularly noteworthy and promising practices. For example, the City of Nashville anticipated potential backlash against speed-management efforts and thus chose to work with advocacy groups to identify areas of the city desiring walkability improvements. By installing walkability improvements in those areas first, city leaders created instant wins that could be used as leverage for future projects.

The authors of the synthesis found there may be a need for greater clarity about the speed-limit-setting process, as well as for greater collaboration between local and state agencies when state roads run through urban areas. In particular, it may be worth exploring whether there is a need for a framework that will foster collaboration between local and state staff on safety initiatives such as achieving flexibility in roadway design, changing laws or regulations that govern speed-limit setting, and finding a balance between local safety needs and regional mobility needs. Such a framework may support both local and state agencies attempting to address safety issues and reach larger goals as articulated through movements like Vision Zero.

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