Impact of 30 km/h zone introduction on vehicle exhaust emissions in urban areas

Abstract

One of the most common traffic management schemes used in Belgium today is the conversion of entire districts, streets or street sections into 30 km/h zones. This is usually done in residential areas where the previous speed limit was 50 km/h. These measures, aimed at increasing traffic safety, are usually seen or even promoted as beneficial to the environment because of reduced fuel consumption and emissions. These claims however are unsubstantiated and stem from the believe that speed reduction measures in urban areas have similar benefits as those on highways. In contrast to this popular believe, wide spread emission estimation methods using quadratic functions such as the Copert/MEET approach would lead us to believe that emissions may rise dramatically. To shed some light on the problem we have calculated emissions for specific types of modern cars with the VeTESS-tool using real-life urban driving cycles. A comparison was then made with artificially modified driving cycles limiting the top speed to 30 km/h where appropriate and elongating the cycle to preserve the original cycle distance. Results indicate that emissions of most classic pollutants should not be expected to rise or fall dramatically. Nevertheless VeTESS results indicate that some emissions such as PM exhaust from diesels may show a significant decrease, whereas MEET functions assume a moderate increase. Exposure of residents to one of the most toxic components of the urban air pollution mixture may therefore also decrease.