Air Quality Effects of Travel Changes

Travel behavior in northeastern Illinois was examined for the 20-year period between 1970 and 1990 by conducting a comparative analysis of data from the Chicago Area Transportation Study 1970 Home Interview and the 1990 Household Travel Surveys. This study identified regional travel conditions and needs and provided an overview of the changes that have occurred because of population and employment growth and behavioral shifts. By understanding travel behavior and patterns in the region and resulting congestion and air quality effects, travel reduction strategies could be developed to promote mobility and meet environmental objectives. The analysis offers insight into travel purpose, mode, location, and length while identifying characteristics of the population making those trips. Changes in travel during the 1970 to 1990 period include increased total daily trips, person miles, and private automobile use, primarily single-occupant vehicle trips; substantial growth in suburban travel; increased work trips, transit and automobile trip lengths, and trip-chaining; reduced passenger trips and automobile occupancy rates; and increased suburban transit ridership. These travel changes have increased traffic congestion and affected air quality. Advances in technology have increased vehicle efficiency. The relative contributions to emissions changes that can be attributed to technology and to underlying behavioral changes are examined. Transportation management strategies can be applied to increase the efficiency of transportation facilities and further improve regional air quality.