Trip chaining: linking the influences and implications
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Transportation analysts have monitored with interest the emergence of trip chaining, or multi-purpose trip making, which is becoming a common method of travel for many households. As of 2001, 61% of all working age adults trip chained. From a policy perspective, this warrants attention as these 61% of adults who trip chain generate 68% of average daily vehicle miles traveled (VMT). In addition, most trip chaining is accomplished by automobile and generally alone or with other family members. Trip chaining research has focused predominantly on travel by workers and findings suggest that one reason for its increase is that workers are scheduling non-work activities into their work commute, largely to support household needs (primarily childcare but also for shopping and personal business). Since the 1990s, significant federal funding has supported programs to improve air quality through reduced emissions. These include employer-based programs that seek to reduce VMT through ride sharing and the use of transit, along with incentives for doing so. The success of these programs is based on the flexibility of the commuter to change his/her work mode. As indicated above, however, trip chaining is typically associated with decreased flexibility and almost in direct conflict with programs that encourage alternative commute modes. This research identifies household, demographic, work, and activity setting factors that influence trip chaining in order to understand the related policy implications for employer-based programs that seek to reduce VMT through encouraging alternative commute modes. Using the 2001 National Household Travel Survey, a market segmentation identified trip chaining influencers. These were primarily the presence of children under the age of 16, worker status, more than one household adult, a high vehicle-to-worker ratio, and educational attainment above the high school level. The findings indicate that while between 30 and 42% of workers commute in the traditional manner, employer-based programs can achieve greater returns if increased focus is placed on improving employer amenities. In addition, further VMT reduction can be achieved through new programs that target the household instead of the employer, as evidenced by the TravelSmart program in Australia and SmartTrips program in Portland, OR.