Although it is widely assumed that congestion causes an increase in emissions, it has always been difficult to quantify this relationship. The project Emissions and Congestion, commissioned by the Transport Research Centre of the Dutch Ministry of Transport and the Ministry of Housing, Spatial Planning and the Environment, investigated this relationship by measuring traffic conditions and corresponding vehicle emissions. Emission factors for different traffic conditions, ranging from free flow to heavy congestion, were derived. With these, total levels of emissions on a number of specific routes and on the entire Dutch motorway network were calculated. The emission factors were also used to asses changes in traffic conditions on specific parts of the network (less or more congestion, introducing a universal speed limit of 100 km/h, and the use of back routes to avoid congestion). From the results it can be concluded that reducing congestion has the largest effect on exhaust emissions on specific congested routes or sections. Lowering the speed limit for passenger cars to 100 km/h on all motorways can also reduce emission levels. Increased congestion leads to substantial increases in emissions. And unless there is serious congestion on the highway, using back roads to avoid congestion should be discouraged. (A)
Abstract