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Safety Effects of Transit Signal Priority: Magnitude and Mechanism
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2020-02-14
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[PDF-1.99 MB]
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Abstract:Previous studies have found a correlation between the implementation of transit signal priority (TSP) and a reduction in vehicle crash rates through aggregated analysis. To understand how TSP affects safety, this study engages a more in-depth evaluation. In this study, the effects of TSP are evaluated on a surrogate safety measure - bus movement roughness - which the authors expect to be closely linked with the risks of bus-related crashes and in-vehicle passenger incidents. Metro Transit of Minneapolis-St. Paul implemented TSP at 30 signalized intersections on bus route #5 in early 2019. Bus crashes and incidents, automatic vehicle location (AVL) records, TSP request log, weather and roadway geometric data were obtained for April-June 2018 and 2019, covering the time periods before and after TSP implementation. Linear regression and tree-based model analysis was carried out on 23,123 event-level observations, with an event defined as a bus approaching and clearing a signalized intersection. The analysis results indicate that the overall bus movement roughness did not change significantly after TSP implementation. However, with a TSP request, the bus movement roughness is significantly smoother than without a TSP request. intersections with more incidents and more crashes are significantly associated with rougher bus movements. Although the effect of TSP on bus movement roughness is significant, its impact is slight, comparing with the impact of bus approaching speed and road geometric features, which also interact with each other. Implications for transit agencies are: 1) TSP helps improve bus safety and can be implemented without much concerns in terms of safety. 2) Bus operational features and road geometric design factors should be integrated in an improvement plan to achieve an optimal safety outcome.
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