This literature review examines the factors influencing the elevated emission levels from vehicles associated with the cold start phenomenon. Of the factors known to influence cold start emissions, it appears that among the most important are the cooling down period of the engine prior to restart, and ambient temperature. The state of cold start modelling is discussed. It is argued that current cold start models are inadequate and must be improved in order to determine the changes in emission levels associated with traffic management. Future models could include a method to represent the engine warm-up and cool-down profiles at a range of ambient temperatures, coupled with information on vehicle usage. Some thought is also given to how traffic management schemes may affect cold start emissions, although for all types of scheme the effects are currently unknown. (A)

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