The Environmental Transport Association Trust (ETA) of United Kingdom has completed a study for the Department of Environment, Transport and the Regions (DETR) which concludes that air pollution inside cars can be up to five times greater than background concentrations. Pedestrians and cyclists are usually exposed to lower concentrations of pollutants because they tend to be at the side of the road rather than in the middle. Car users are, in effect, travelling in a tunnel of pollutants.