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Open Access Publications from the University of California

It’s Not Just a Sign: Traffic Calming Gives Bump to Safety – A Cost Benefit Analysis ofTraffic Calming in the City of Los Angeles


The Los Angeles Department of Transportation (LADOT) has implemented traffic calming measures across the city, recognizing that collisions may not be preventable but can be reduced in severity through roadway design. The department has a process whereby residents can apply for speed humps on a quarterly basis, but the program is oversubscribed. There are few studies in LA that address the effectiveness and ability to equitably distribute the benefits of traffic calming. This report is framed by the central question: How effective are the low-cost traffic safety interventions that the City of Los Angeles frequently uses on its residential streets? Interventions covered in this study include speed humps, bike lanes, partial closures and stop signs. I used four metrics to evaluate effectiveness, including traffic speed, traffic count (ADT), collision frequency and collision severity. I conducted paired sample t-tests to compare speed and volume one year before and after measures were introduced. Additionally, I used the Statewide Integrated Traffic Records System (SWITRS) to evaluate collisions. The results of this study show that speed humps are the most cost-effective and proven method of traffic calming included in this analysis. The severity and number of collisions reduced as a result of introducing all measures. Design measures that make a road less viable for thoroughfare like partial closures can reduce cut-through traffic and related collisions. At minimum, LADOT should consider restructuring the petitioning process by lowering the threshold to apply for speed humps and prioritize key places like schools and low-income communities.

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