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 on general. For a big part of the whole 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. Complex models, which are - at least in general - capable to consider al the necessary details can be operated only for single situations, they are not able to calculate dispersion in the context of a statistical simulation. There exists a gap between simple - but operational - street models, which do not consider e.g. the momentum of exhaust air from tunnel portals, and complex CFD models, which can not be used in an operational way. Aim of this project will be to investigate and parameterise the effects of street tunnel portals on the diffusion process (e.g.: momentum of exhausts, temperature differences between tunnel exhausts and ambient air, traffic induced turbulence) and to develop and validate a new model for operational use. Due to the fact that city tunnels will be located in built up areas mostly close to buildings, complex features like noise abatement walls should be considered as well as dispersion under low wind speed situations. The project would therefore cocentrate on field measurements in the vicinity of existing tunnel portals. Based on the experimental data, existing models shall be improved and validated.