Analysis of Urban Area Automobile Emissions According to Trip Type

Travel data from the Pittsburgh transportation survey and emissions data developed by the Environmental Protection Agency have been used to estimate Allegheny County (Pittsburgh), Pennsylvania, automobile emissions according to trip purpose, length, origin, and destination. The results include estimates of diurnal evaporative emissions, cold-start and hot-soak emissions, and actual running emissions. Home-based work trips and trips to and from the central area of the county each produce one-third to one- half of Allegheny County automobile emissions and are the dominant causes of automobile emissions in the county. Cold starts and evaporations produce approximately half of the hydrocarbons and a quarter of the carbon monoxide. Trips shorter than 5 miles and trips longer than 5 miles produce roughly equal quantities of carbon monoxide and hydrocarbons. However, long trips produce greater quantities of nitrogen oxides. These findings suggest that improved peak-period and radial transit may be effective in improving air quality through reducing automobile travel if such transit reaches peripheral areas of the county. However, cold-start and evaporative emissions may significantly impair the effectiveness of transit approaches that rely on the automobile for residential collection and distribution.