Pollution Dispersion from Covered Roadways and Tunnelportals

Road traffic is a prerequisite for a functioning transport system in urban areas. Although there are many political activities to shift passenger transportation to other transport modes in urban areas, still a big part remains and, concerning the commercial sector, needs to take place on the street network. Policy is now to separate between traffic calming zones and a highly effective main street network. Mainly noise is recognised as one of the major problems of urban air traffic. In order to overcome problems related to land use and nuisance due to noise, covered roadways or city tunnels are an appropriate solution. Beside the effect of eliminating the noise problem, the characteristic of the built up land is not interfered by high capacity roads. But at least one problem remains in general - pollution due to exhaust gases is shifted towards the two portal regions in general. For a big part of the region the air quality will be improved, but for those two areas, it will definitely become worse. In order to estimate pollution at the portal locations, it is absolutely necessary to use appropriate dispersion models. But here a problem arises. Simple dispersion models, which can be used in an operational way, concentrate on street scale, avoiding too complex situations like junctions and tunnel portals.