Abstract:A series of surveys was conducted at four San Francisco Bay Area firms in 1979 to stUdy the effect of flexible work hours on choice of mode for the work trip. Analysis of nearly 1200 individual responses showed consistent and statistically significant decreases in solo driving, even after mode changes that were estimated to be caused by 1979 gasoline shortfalls and skyrocketing energy prices were screened out. Individuals who changed to transit were found to be from generally lower-income households and thus susceptible to gasoline price increases; flextime further assisted their shift to transit by alleviating anxieties about being late for work due to unreliable transit service. These individuals frequently traveled during the off-peak hours, when seats were more readily available. Individuals who changed to ridesharing ranked congestion avoidance as high or higher than the ability to coordinate work schedules with fellow carpoolers (frequently a working spouse for employees at three downtown firms). Although there were diversions from ridesharing to transit, the net result was a statistically significant increase in ridesharing. The evidence from these four Bay Area firms strongly suggests that flextime is complementary to transit marketing and ridesharing promotions, although the net change in mode share is likely to be modest (less than 5 percent).