Comparison of VSP profiles for three types of intersection control and implications for emissions

Roundabouts have generally been considered to have lower emissions as compared to signal controlled and 4-way stop-control intersections since they improve traffic flow and average speed. However, roundabouts slow all vehicles to speed ranges where emissions are higher, while signals stop and delay only a portion of vehicles. Roundabouts have the potential to increase the amount of acceleration and deceleration for all vehicles. Emissions are correlated to these modal events, therefore the impacts should be considered in the evaluation of roundabouts. Vehicle activity (instantaneous speed and acceleration) are key inputs to modal emission models such as the US Environmental Protection Agency´s MOVES. The objective of this paper was to compare the vehicle activity of a roundabout to 4-way stop control and signal controlled intersections. The paper presents result of a study which collected second-by-second vehicle activity on-road along a corridor in Urbandale, Iowa. Vehicle activity for the three different types of traffic control was compared.