Traffic Conflicts in Expressway Merging

The risk of collision in an expressway merging process is investigated using the traffic conflict technique. The severity of conflict in a merging event is quantified by a measure that is the inverse of the time measured to collision. To determine this measure, recordings of merging events were obtained at a merging area of an expressway in Singapore over eight periods, and the arrival times of vehicles at constantly spaced intervals were subsequently extracted in the laboratory. The errors in the data‐collection process were minimized by using two video cameras simultaneously in the recording process to increase the size of images and playing back the tapes at a lower speed during data extraction. The systematic errors in the data due to observers' bias were also estimated to facilitate data adjustment. Based on the adjusted data, the computed measure from about 200 merging events in each observation period was found to be best fitted by the mixed Weibull distribution. Using the tail end of the distribution, the probability of near‐accident per merge in each period was estimated.