Traffic signal change and clearance interval design and intersection risk assessment

Red light running and the associated risk and crashes at signalized intersections have been an ongoing concern to many safety engineering professionals. The proportions of crashes that occur due to such driver behavior represent a majority of crashes at urban and suburban signalized intersections. Many initiatives to discourage red light running have been implemented throughout the United States, including public awareness campaigns, automated enforcement programs and various engineering countermeasure. These efforts have affected the overall crash statistics in the nation, which show a reduction in red light violations related crashes over the past several years.; A series of evaluation studies were conducted in order to test the effects of a change and clearance intervals calculated according to ITE guidelines on late exits (LE) and red light violations (RLV) at 12 signalized intersections in Southeast Michigan. This included a ‘before and after’ study of three intersections in Oakland County, Michigan and a comparative parallel study of nine intersections in Detroit. The risk associated with vehicles that have not cleared the intersection when the cross-street light turns green (late exit) was evaluated.; Models were developed as a part of this research to assess the risk of LE and RLV at signalized intersections in Michigan. The models were developed using regression techniques for a linear additive model. One model was developed for intersections with all-red intervals and the second model was developed to assess intersection risk at intersections without all-red intervals. To develop the models, angle crash frequency was used as the dependent variable and late exit rate, red light running rate and the deviation of approach speed as compared to the speed limit were used as the independent variables.; The main conclusion of this study found that the red light running experience at the ‘before’ and ‘after’ periods at the Oakland County sites, and at the test (with all-red intervals) and control sites (without all-red intervals) in Detroit, were not significantly different. However, the risk related to potential angle collisions is significantly less at the test sites, where appropriate all-red intervals are installed, as observed through the late exit experience at the study sites. Thus, late exits were identified as they key factor in assessing intersection safety risks.