J. Kaistinen, T. Nieminen, H. Summala
Reasons for the known capacity and safety benefits of the split 2+1 roads were studied on-road, by measuring driving behavior with a floating vehicle method and roadside videotaping. Measures from a split 2+1 lane road and a two-lane wide-shoulder road were compared. The 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, which means more relaxed passing maneuver, but also hindering some vehicles behind from passing. The split 2+1 road didn’t generate more speeding than the wide-shoulder road, but over 80 % of the passing vehicles exceeded the speed limit (100 km/h) on both road types. The 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 the passing lanes did not cause major disturbances in the traffic flow. Occasional reduction in vehicle velocities, and brakedowns of traffic flow occurred during peak rush-hours on the longest (4 km) no-passing segment of the road. According to the road side interviews, majority of drivers seem to accept and prefer the 2+1 lane road.
Keywords: 2+1 lane road; passing lanes; traffic safety; capacity; passing; wide-shoulder road