Traffic signal coordination: a measure to reduce the environmental impact of urban road traffic?

Coordinated traffic lights that implement green waves along major arterial roads are an increasingly used traffic management strategy for reducing travel times in urban context. The potential positive effect of this measure on emissions is often called upon as an additional support for its introduction. Although a smoother traffic flow will generally lead to lower air pollutant emissions, it will not necessarily lead to lower noise emissions. Because of the challenges associated with measuring the emissions caused by a stream of vehicles, up to now, little scientific research has been spent on the effects of synchronized traffic lights on emissions. This paper presents the results of a computational study on the effects of traffic signal coordination on vehicle emissions along an arterial road. The methodology consists of coupling a microscopic traffic simulation model with state-of-the-art models for instantaneous emission of noise, carbon dioxide, nitrogen oxides and particulate matter. The influence of traffic intensity, signal timing and signal coordination parameters is investigated through the simulation of a wide range of scenarios. The introduction of a green wave was found to reduce air pollutant emissions by up to 40% in the most favorable conditions, depending on traffic flow and signal timing settings. Sound pressure levels were generally found to decrease near the traffic signals, but to increase in between intersections.