Calculation of Changes in Drive-Alone Commute, Vehicle Miles Traveled, during Temporary Freeway Closure

Abstract

A 1-mi stretch of Interstate 5 in downtown Sacramento, California, was closed intermittently for reconstruction (i.e., “the Fix”) in the summer of 2008. With data collected from two contemporaneous surveys of affected workers, the study reported in this paper estimated changes in drive-alone commute, vehicle miles traveled (DACVMT) as a result of Fix-related mode shifts, switches to (increased) telecommuting (TC) and compressed work week (CWW) schedules, personal leave (PL) days, and departures from the region (DFR) (i.e., out of town for the entire study week). Distinctions were made for the first three causes for the changes, which were characterized as possibly permanent, and the latter two, which were definitely temporary. Net DACVMT changes were distinguished further by respondents who made overall positive changes and overall negative changes. During the target week, the total Fix-related VMT reduction for the entire affected sample (N = 6,185) was estimated to be between 5.36% and 5.48%. Reductions from potentially permanent sources led to an estimated 4.08% to 4.21% reduction, and those from definitely temporary sources led to a 1.27% reduction. Mode shifts reduced DACVMT between 3.04% and 3.17% (the net of a 0.42% increase by 32 respondents and a 3.46% to 3.59% decrease by 257 respondents; seven respondents made drive alone–related mode shifts that resulted in no net DACVMT change). Increased TC and CWW engagement contributed additional 0.71% and 0.33% reductions, respectively. PL time and DFR reduced DACVMT by 0.15% and 1.12%, respectively.