Predicting Pollution

by William Loudon, Assoc. V.P.; JHK & Assoc., Emeryville, CA 94608,
Malcolm Quint, Transportation Engr.; JHK & Assoc., Emeryville, CA,

Serial Information: Civil Engineering—ASCE, 1993, Vol. 63, Issue 4, Pg. 66-67

Document Type: Feature article


For urban areas struggling to meet the requirements of the 1990 Clean Air Act as well as state air-quality mandates, accurate forecasting of mobile emissions is critical to evaluating transportation-control strategies. Mobile emissions models have generally been based exclusively on VMT and average link speed, but research has shown that vehicle emissions should be divided into at least four categories: (1) trip-start emissions, (2) running emissions, (3) evaporative trip-end emissions and (4) diurnal emissions. Travel speed also affects emissions of the primary mobile pollutants (hydrocarbon, nitrogen oxide and carbon monoxide). Other factors include vehicle type and time of day. Fortunately, recent advances in automation have made it easier to use output from existing regional transportation models to estimate areawide emissions and evaluate transportation-control measures. These new methods offer significantly more accurate predictions without much change in the methods used by regional planners, and at very little added operation costs.

Subject Headings: Pollution

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