Assessing the impact of converting roundabouts to traffic signals on vehicle emissions along an urban arterial corridor in Qatar.

Abstract

The type of control at intersections has a major effect on the operation of any urban corridor. Different pre-defined procedures are available to calculate some of the main operational characteristics, such as capacity, delay, and level of service in order to select the best type of control. However, there are other important factors that affect major arterials operational characteristics, which are not fully addressed, such as the impact of emissions. In this study, a microscopic simulation approach using VISSIM and MOVES was developed to assess the environmental effect of converting four three-lane roundabouts to signalized intersections along a heavily congested urban corridor in Qatar. A decision was made to switch all roundabouts to traffic signals for better operations. Preliminary results indicated that the signal control outperformed the roundabout in the range of 37% to 43% reduction in emissions. A more detailed analysis revealed that roundabout corridor operations effect on emission rates are divergent from signalized corridors, particularly upstream and downstream of the intersections. Immediate roundabout upstream approaches are driver behavior dependent; characterized by substantial coasting at lower speeds and subsequent re-accelerating with less idling, described as acceleration events, which resulted in high emission rates while signalized corridors' s are signal timing dependent; characterized by ample idling with less coasting and re-acceleration, resulting in reduced emission rates. The results also revealed that there was no significant difference between emission rates in the vicinity of the two types of control. Both recorded nearly the same emission rate.