DRIVING BEHAVIOR ON SPLIT 2+1 LANE ROAD

This research studied reasons for the known capacity and safety benefits of the split 2+1 roads by measuring driving behavior with a floating vehicle method and roadside videotaping. Measures from a split 2+1 lane road and 2-lane wide-shoulder road were compared. Results showed that drivers appeared to take advantage of the improved passing opportunity on the 2+1 road and passed more vehicles at once. Passing times of a single passed vehicle at once were clearly longer on the split 2+1 road, indicating a more relaxed passing maneuver, but also hindering some vehicles behind from passing. The split 2+1 road did not generate more speeding than the wide-shoulder road, but over 80% of the passing vehicles exceeded the speed limit on both road types. Transfer of passing behavior from a split 2+1 road to the subsequent wide-shoulder road was also studied, but no effects were found on gap acceptance. Passing vehicles merging to the base lane at the end of passing lanes did not cause major disturbances in traffic flow. Occasional reduction in vehicle velocities and brakedowns of traffic flow occurred during peak rush hours on the longest no passing segment of the road. According to roadside interviews, a majority of drivers seem to accept and prefer the 2+1 lane road.