The advance of motorized traffic has brought our attention to its disadvantages. Noise and exhaust gases do not just annoy people, they threaten human health and welfare. This book reports the scarcely available measurements of emissions to which adverse health effects are attributed. From these data it appears that although hardly any particular health effect can be scientifically proven to be caused by road traffic combined these effects strongly indicate that public health is endangered and action should be taken. The 1950-1980 efforts by the US government to formulate exhaust standards for cars are used to illustrate the political difficulties inherent in such undertaking.