  Commuting, like other types of human travel, is complex in nature, such as
trip-chaining behavior involving making stops of multiple purposes between two
anchors. According to the 2001 National Household Travel Survey, about one half
of weekday U.S. workers made a stop during their commute. In excess commuting
studies that examine a region's overall commuting efficiency, commuting is,
however, simplified as nonstop travel from homes to jobs. This research fills
this gap by proposing a trip-chaining-based model to integrate trip-chaining
behavior into excess commuting. Based on a case study of the Tampa Bay region
of Florida, this research finds that traditional excess commuting studies
underestimate both actual and optimal commute, while overestimate excess
commuting. For chained commuting trips alone, for example, the mean minimum
commute time is increased by 70 percent from 5.48 minutes to 9.32 minutes after
trip-chaining is accounted for. The gaps are found to vary across trip-chaining
types by a disaggregate analysis by types of chain activities. Hence,
policymakers and planners are cautioned of omitting trip-chaining behavior in
making urban transportation and land use policies. In addition, the proposed
model can be adopted to study the efficiency of non-work travel.
