Crashes at signalised intersections account for approximately 20% of all crashes both nationally and within the State of Minnesota. Past research suggests that the use of all-red clearance interval at signalised intersections may reduce intersection crashes, particularly those related to signal violations. Other research suggests that this reduction may only be temporary. This research evaluates the safety effect of all-red clearance intervals at low speed urban 4 way intersections in the City of Minneapolis. The study includes a review of literature and assessment of Midwestern state and local practice related to the use of all-red phasing. A cross-section analysis using four years of data is presented, which does not substantiate any safety benefit of all-red phasing at study area intersections. Several regression models (generalized linear mixed models with Poisson error distribution and log link function and linear mixed models with transformed data) are also presented. The models also point to no safety benefit. A before and after analysis using 11 years of data was conducted to evaluate both short and long term effects. While results indicate short-term reductions in crash rates (approximately one year after the implementation), long-term reductions are not observed. (Author/publisher)
Abstract