Driving patterns and emissions from different types of roads

Abstract

The project evaluates the relationship between emissions and travel speeds on different types of roads such as city streets, highways, express roads and motorways. Approximately 800 measured driving patterns of 13 streets and roads have been analysed and emissions have been predicted in an emission model, also taking into account deterioration factors and cold start emissions. The result of the analysis is a clear relationship between travel speed (trip length divided by trip time) in the range of 10–120 km/h and emissions from all vehicle types. For petrol-powered passenger cars catalysts reduce HC, CO and NOx emissions by 70–80% on main roads and by 60–75% on city streets. The difference is due to the proportion of cold engines in city traffic. In city streets, 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 crucial to the level of emissions. However, express roads have slightly higher emission levels than motorways at similar travel speeds, presumably because traffic flows are less steady on express roads than on motorways.