The Environment Act 1995 has confirmed that traffic regulation orders, and hence traffic management schemes, may be used for the purposes of air quality management. One form of traffic management -traffic calming - has been found to be particularly effective at reducing vehicle speeds, as well as the frequency and severity of accidents. However, there is little information relating to the effects of different traffic calming measures on vehicle exhaust emissions and ambient air pollution. In order to provide information and guidance for local authorities, TRL was commissioned to undertake a study on behalf of the Charging and Local Transport Division of DETR. The main objectives of the study were to investigate the effects of nine different types of traffic calming measure on the exhaust emissions from passenger cars, and to develop a system of performance indicators for the measures. These indicators accounted for effects on emissions from all road traffic, and demonstrated how emission impacts compared with impacts on speed, safety, and delays to emergency service vehicles. Driving cycles were formulated to represent vehicle operation before and after the introduction of the measures, based on in situ traffic survey data, and the emissions from a range of passenger cars were then recorded as they were driven over the cycles on a chassis dynamometer. The mean emission rates of CO, HC, NOx, and CO2 from petrol non-catalyst, petrol catalyst, and diesel cars increased by up to 60% following the introduction of traffic calming measures. However, it was estimated that the increased emission rates were unlikely to have resulted in poor local air quality. (A)

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