National Academies Press: OpenBook

Pedestrian Safety Relative to Traffic-Speed Management (2019)

Chapter: Chapter 4 - Conclusions

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Page 65
Suggested Citation:"Chapter 4 - Conclusions." 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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Page 65
Page 66
Suggested Citation:"Chapter 4 - Conclusions." 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.
×
Page 66
Page 67
Suggested Citation:"Chapter 4 - Conclusions." 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.
×
Page 67
Page 68
Suggested Citation:"Chapter 4 - Conclusions." 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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Page 68

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65 This synthesis aimed to document the extent of knowledge and understanding about using traffic-speed management to improve pedestrian safety in the United States. To accomplish this task, the project employed a literature review of countermeasures known to reduce speed effectively and interviews with cities known to be working to improve pedestrian safety via traffic- speed management. 4.1 Key Findings The literature review revealed a host of countermeasures that are effective at reducing speed, such as speed humps and speed bumps (examples of vertical deflection) and chicanes of mini traffic circles (examples of horizontal deflection). However, the bulk of the countermeasure literature covers treatments more appropriate for local roads or lower-speed collectors. While these countermeasures are important for those circumstances and are critically important for particularly low-speed areas such as school zones, they are often not recommended or allowed (via local policy) on the higher-speed streets typically associated with the highest injury sever- ity for pedestrians. For that context, redesigning the street 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, the most effective current solution seems to be enforcement, and particularly 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 interviews revealed a wide variety of efforts among cities aiming to improve pedestrian safety via traffic-speed management. Many of these cities employ the treatments covered in the literature review. 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 influenced the types of treatments that were considered feasible for each city. Thus, although the City of Seattle has found success using ASE in school zones and reconfigurations for several major streets, 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 note- worthy and promising practices. For example, the City of Nashville anticipated potential backlash against speed manage- ment 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, the City C H A P T E R 4 Conclusions

66 Pedestrian Safety Relative to Traffic-Speed Management created instant wins that could be used as leverage for future projects. The City of Los Angeles has begun piloting the use of real-time, aggregated speed data from speed feedback signs. The signs provide instant feedback to drivers who pass by, alerting them of their too-high speed, and can send anonymized data to the City’s police department to alert them of speeding in certain areas. The police can then patrol those areas and issue citations as needed. Thus, the City is able to still use technology to help enforce the speed limit, but without identifying any one individual. This creative thinking is helping these cities pursue Vision Zero in a way that works for their context, which can provide helpful examples for and inspire others. The interviews also covered barriers to speed reduction and lessons learned from each agency’s efforts. For example, several interviewees discussed the importance of extensive community engagement to ensure a project’s success. Additionally, many interviewees reported feeling con- strained by the 85th percentile rule and a lack of ability to work around it even on roadways where speed is a known problem and data show safety to be a problem. While each agency had several success stories from their efforts, they have also learned along the way what works better or worse for achieving goals within their context. 4.2 Considerations As stated in the Introduction, this synthesis reflects a relatively new—albeit critically important—focus of the traffic safety community. For this reason, the literature review addressed speed by looking at countermeasures known to reduce speed, even if pedestrian safety had not been a consideration in the study, and the interviewees reflect agencies at the vanguard of the effort, as opposed to a more ideally geographically dispersed, diverse set of responses. Additionally, some the findings reflect practices that are considered promising rather than proven. At the same time, this synthesis seeks to fill a gap in current information about how cities are addressing pedestrian safety via traffic-speed management and reveals gaps that future research could seek to fill. 4.3 Suggestions for Future Research This report identified the following gaps in the literature and practice that are ripe for further exploration. Understanding of Effectiveness of Traffic-Speed Management Efforts Related to Pedestrian Safety: There is a need to understand how effective the various speed-reduction counter- measures are for pedestrian safety, both individually and in combination. Although speed reduc- tion should logically result in both lower pedestrian crashes and lower injury severity, research is often conducted without sufficient time for such crashes to be measured in a statistically rigorous way. Therefore, field research designed to measure the impacts of speed management efforts specifically for pedestrians, whether over a longer period of time or via a multiple-site case–control study (see, e.g., Zegeer et al. 2002), would be a helpful addition to the literature. Relatedly, there is a need for research that looks at surrogate safety measures (e.g., conflicts such as near misses) within these same scenarios, given the difficulty of relying on crash data to show changes in pedestrian safety over a short period. This research would relate such conflicts to eventual crash outcomes, but could provide shorter-term feedback on risk and, if coupled with intercept surveys, perceived risk. Expanding the research to examine the effects on other modes would further increase the profession’s understanding of the potential overall effect of various speed management efforts.

Conclusions 67 Information about Effectiveness of Countermeasures and Combinations within Various Contexts: Additionally, it is conceivable that certain countermeasures and countermeasure combinations work better for improving pedestrian safety than others or work better in some geographic or land use contexts than others. Information about effectiveness of speed management efforts in various combinations and contexts is important for cities specifically seeking to improve pedestrian safety via managing traffic speed. Understanding of Spillover Effects: There is also a need for more information about the long-term impacts and geographic extent of reduced vehicle speeds that result from the various countermeasures, as well as for information about whether and by how much volumes are diverted to other areas, potentially creating safety problems elsewhere. Exploration of Perceived Safety Impacts: Another area of interest is that of perceived safety relative to these treatments. For example, if a pedestrian feels safer crossing a street with a certain treatment, that is important information to consider when choosing among treatments, all other things being equal. Treatments that have not been well researched include many of the engineer- ing treatments that horizontally deflect traffic, such as curb extensions, neckdowns, chicanes, mini traffic circles, lane narrowing, and reduced corner radii. Evaluation of Comprehensive Programs: The effectiveness of comprehensive programs, such as Vision Zero or even just a traffic-calming program, is also an area of keen interest and is ripe for study. These programs also present an opportunity to collect data on treatments that are not well studied. For example, many cities have implemented curb extensions or chicanes as part of traffic-calming programs, despite a lack of academic evidence indicating the impacts of these treatments. Because these installations often require before data to be captured to justify the treatment, they provide a starting point for more comprehensive before–after evaluations to be conducted. Additionally, education and outreach are key elements of comprehensive programs that remain understudied, despite being believed to be important. Additional Solutions for Traffic-Speed Management along Arterials: There is also a need for solutions for higher-volume, higher-speed roadways like arterials, which tend to be the locations of the most injurious crashes—both for pedestrians and overall (excluding highways for motor vehicles). While some countermeasures appropriate for arterials have been developed, they are often prohibited by state law (as in the case of ASE) or may be politically sensitive (e.g., recon- figurations). In other cases, the solution may involve slight modifications to the countermeasure or to the roadway to allow the countermeasure to work. Additional thinking and exploration in this realm could benefit the profession. Examination of the Role of Driving Culture: It is also true that in some cases, lower speeds on these roadways will necessarily change their character and perhaps their function within a community, potentially affecting roadways in other parts of the community. These complica- tions relate to a fundamental issue that can make speed management more difficult in general: When people are accustomed to—and even depend on—driving a high speed to go about their daily lives, this can contribute to a driving culture that resists change. This is often true, even when people recognize speeding to be a problem: A 2015 survey by the AAA Foundation for Traffic Safety found that 89% of respondents considered it unacceptable to drive 10 mph over the speed limit on a residential street, but 45% admit to having done so within the last 30 days (AAA Foundation for Traffic Safety 2016). Thus, in addition to the need for additional speed- reduction solutions or strategies on higher-volume, higher-speed roadways, this synthesis points to a need for research regarding facilitating behavior and culture change related to speed and auto dependence. Understanding of Speed Limit-Setting Process: The interviews also revealed a desire for addi- tional control within cities over setting their speed limits, but a lack of clarity about how to gain

68 Pedestrian Safety Relative to Traffic-Speed Management that control. This was true for local roads as well as state roads within a community, but the state roads were associated with the additional complication of also not necessarily being under design control of the local jurisdictions—even when safety problems were present that cities wanted and felt obligated to address. At the same time, state agencies also lack some authority over their roads if speed limits are set based on a process established by state law. A resource that articulates the process for speed-limit setting within each state, including key decision makers and decision points, would help practitioners understand the process and more efficiently target any efforts to modify it. Framework for Intra-Agency Collaboration: Finally, the complex interaction of respon- sibility for local and state speed-limit setting points to a need for a framework that can foster collaboration between city and state agencies and legislative authorities, as well as federal agencies where applicable, to achieve safety goals. This need was illustrated by the California case example, which shows multiple agencies attempting to modify standards to better respond to cities’ requests for additional control, but without a clear path to do so. The need for this process is likely to only increase as more cities prioritize safety issues (e.g., through the adoption of Vision Zero) and if speed management efforts reveal positive impacts on pedestrian safety in particular, as well as traffic safety in general. It is hoped that this synthesis provides helpful information for practitioners seeking to improve pedestrian safety via traffic-speed management and inspires creative thinking and contributions to the field that can help fill these gaps in knowledge and understanding.

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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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