Evaluation of safety and operational aspects affecting roadway intersections: Prioritizing procedure for improvements, traffic signal installation, driving behavior, and clearance interval

Transportation engineers consider that roadway improvements and the priority of the implementation of improvements to the existing conditions of roadway systems are essential as urban population and traffic volume increase. Regarding intersections, analysis needs to consider the safety and operational conditions of the location for potential improvements. Intersections present complex conditions that produce vehicle conflicts among road users because of entering and crossing movements within its influence area, which could cause safety and operational problems at these locations. This dissertation presents research regarding several safety and operational aspects related to intersections. For the safety aspects, a procedure to prioritize intersections for improvements considering safety and operational factors is developed, and an evaluation of the installation of traffic signals on crashes at intersections is performed. For the procedure, three different lists are generate based on B/C ratio; on average delay before improvements and delay reduction after improvements; and based on B/C ratio, average delay before improvements, and delay reduction after improvements. For the evaluation, crash prediction models to estimate the number of crashes at intersections before and after signalization were developed. The models could be used to estimate the changes in total number of crashes and number of crashes by type.; For the operational aspects, differences in driving behavior of different driver age group, and clearance time for left turning vehicles at signalized intersections are investigated to determine their effects on the operational performance of intersections. In reference to driving behavior, longer reaction time of older drivers may cause longer start-up lost time or saturation headway at signalized intersections, which might have impacts on intersection capacity and drivers' safety. For clearance time, intersections with different geometric characteristics, posted speed, left turn treatment, and percentage of heavy vehicles making left-turn were selected. Results indicated that if the same time is used for clearance and change intervals for left-turn and through movements at intersections, safety and operational problems might arise.