What Counts as Commute Travel? Identification and Resolution of Key Issues around Measuring Complex Commutes in the National Household Travel Survey

We use travel diary data from the 2017 National Household Travel Survey (NHTS) Georgia subsample to address critical issues associated with analyzing complex work journeys. To define the work journey, we discuss the importance of defining commute anchors by both purpose and location. We then compare two alternate measures for determining what portion of each journey should be counted as commute distance: the last leg of the journey (the NHTS default), and a modeled counterfactual simple commute to estimate the distance that would have been traveled had no stops been made. The average complex commute distance obtained using the counterfactual method was 63% higher than the estimate based on using the last leg alone. Using the last-leg method may understate Georgia's annual commute distance by 2.6 billion miles (10% of the total, including both simple and complex commutes). We argue that the last-leg method is not an accurate gauge of work travel, particularly among populations such as women, who are more likely to trip chain on their commutes.

Automated summary

By utilizing travel diary data from the 2017 NHTS Georgia subsample, this study addresses critical issues related to analyzing complex work journeys and discusses the importance of defining commute anchors based on purpose and location. Comparing two methods for determining commute distance, it was found that using a modeled counterfactual simple commute resulted in an average 63% higher estimate of complex commute distance compared to using the last leg method. This suggests that the last-leg method may underestimate Georgia's annual commute distance and is not accurate for measuring work travel, especially for populations such as women who are more likely to chain trips during their commutes.