Estimating Impacts of Transportation Control Measures on Work-Related Trips

States and metropolitan areas are under increasing pressure to implement transportation control measures (TCMs) to reduce mobile source emissions. Many of these TCMs are aimed at commute trips (i.e., trips from home to work and back). A number of techniques are used to analyze the TCMs. Models use home-based work (HBW) trip tables as input; these consist of the trip from home to work and the trip from work to home, which account for 25 to 30 percent of all trips in a region. However, analysis of the Home Interview Survey data for Washington, D.C., indicates a large number of the nonwork trips were actually taking place either as part of the trip from home to work or from work to home, or during the workday. If a TCM is analyzed using only the HBW trip table, it is implicitly assumed that there will be no impact on the trip from home to work with an intermediate stop. However, it is possible that the TCM could alter the behavior of the person making the home-to-work trip with an intermediate stop. If this is not accounted for, the results of the analysis underestimate the impact of the TCM. Research undertaken for two distinct but related subjects is summarized. The amount of work-related nonwork travel in the Washington, D.C., metropolitan region is estimated, and the methodology developed to account for the effect of TCMs on total work is described.