Impacts of freeway exit ramp configurations on traffic operations and safety

The main purpose of the paper is to evaluate the impacts of freeway exit ramp configurations on traffic operations and safety. Results summarized in the paper are based on a research project sponsored by China Department of Transportation to develop guidelines for safety design of freeway exit ramps in China. The main elements to be considered in freeway exit ramp configuration classification are geometric conditions (such as number of lanes in the upstream and downstream segments of exit ramps), geometrics of deceleration lanes, exit ramp lane configurations, etc. Google Earth was searched to identify many freeway ramp sites in USA, Japan, Europe countries, and China. The exit ramp configurations surveyed through these sites were summarized and categorized into four types. Based on such exit ramp lane configuration classifications, traffic operational and safety performances were analyzed. The main measures of effectiveness for traffic operations and safety are operational speed and traffic crash characteristics, respectively. Thus, for design purposes, adequate exit ramp configurations can be proposed in order to satisfy the operational and safety requirements under different conditions.