The study was made at four grade-separated intersections on a four-lane divided highway. Traffic flow was observed in different road, traffic and weather conditions. Observation using video equipment were made before the acceleration lanes were built and after the completion of the lanes. The total number of observation hours was 22. The capacity of entrance ramps was improved and traffic moved more smoothly after the building of the acceleration lanes. The critical gaps in the merging into the traffic flow of the highway decreased by 1.6 seconds. The mean speeds of vehicles entering from the ramp increased by 10 kmph on a dry and by 4 kmph on a slippery road. Traffic safety at the intersections was also improved after the building of the acceleration lanes. The number of hazardous situations, i.e. conflicts and conflict risks were distinctly lower than before. The clearest improvements in traffic safety as well as in the capacities were observed at the busiest intersections. Merging into the traffic flow on the highway took place in most cases from the latter half of the acceleration lane. Bus stops situated on the extension of some acceleration lanes were found to cause disturbance and increased accident risk for vehicles entering the highway.
Abstract