Speed limits are intended to regulate driving speeds so as to achieve an appropriate balance between travel time and risk for a road class or specific highway section. More importantly, speed limits attempt to increase roadway safety by setting speed limits that avoid crashes and mitigate crash outcomes. Although the relationship between speed limits and safety is recognized, this relationship is complex with a variety of factors. Despite this complexity, transportation agencies rely on relatively simple approaches to determine appropriate speed limits for a roadway. Another approach for setting speed limits is through the use of optimum speeds. Proposed more as a theoretical approach in the 1960s, optimum speed limits are set to minimize both user and societal costs. Despite the lack of application of this approach, recent attempts to control and design roadways using traffic calming measures and context sensitive design may be benefited by setting speed limits using a more optimal speed limit approach. The primary objective of the research described in this paper is to develop a logistic regression model for identifying the relationship between injury severity sustained by pedestrians or bicyclists and a set of independent variables including the posted speed limit on the roadway. Given the relationship between injury severity and geometric, traffic and environmental factors, the optimal speed limits for minimizing severity could be determined.
Abstract