Is Usual Share of Commuting Mode Always Greater than its Actual Share?

With data from the 2001 National Household Travel Survey (NHTS), recent research showed that transit's usual share was greater than its actual share for workers in the United States in a variety of commuter markets. A mode's usual share is the percentage of workers who state that they usually use that mode for commuting in a week, whereas the actual share of a mode is the percentage of work trips by that mode by the same workers on a typical work day. This study explores whether this relative relationship between a mode's usual and actual shares holds true for common modes other than transit for the United States. Mathematically, it is determined that this relative relationship cannot hold true for all modes; in other words, the usual share has to be smaller than the actual share for one or more modes other than transit. Empirically, the same 2001 NHTS is used to test this relative relationship for three common modes—the privately owned vehicle (POV), walking, and biking—and for a variety of commuter markets. The empirical results confirm the mathematical conclusion that the relative relationship holds true for biking but not for POV and walking. In addition, the relationship between usual and actual shares is determined not solely by the mode but also by individual commuter markets. Finally, the deviation between usual and actual shares in percentage terms is large for transit and walking, but small for privately operated vehicles and bikes. One direction of future research would be to determine the reasons for these differences in the usual–actual relationship across modes and commuter markets.