DRIVING PATTERNS AND EMISSIONS FROM DIFFERENT TYPES OF ROADS

The project evaluates the relationship between emissions and travel sp eeds on different types of roads such as city streets, highways, expre ss roads and motorways. Approximately 800 measured driving patterns of 13 streets and roads have been analysed and emissions have been predi cted in an emission model, also taking into account deterioration fact ors and cold start emissions. The result of the analysis is a clear re lationship between travel speed (trip length divided by trip time) in the range of 10-120 km/h and emissions from all vehicle types. For pet rol-powered passenger cars catalysts reduce HC, CO and NOx emissions b y 70-80% on main roads and by 60-75% on city streets. The difference i s due to the proportion of cold engines in city traffic. In city stree ts, when cars with cold engines are included, the emissions of CO and HC from petrol-powered passenger cars are found to be 10-20% and 5-10% higher, respectively. Travel speed - and not the type of road - is cr ucial to the level of emissions. However, express roads have slightly higher emission levels than motorways at similar travel speeds, presum ably because traffic flows are less steady on express roads than on mo torways.