California travel surveys show big shift away from driving

By Chris McCahill

Last year the California Department of Transportation (Caltrans) released the findings from its decennial household travel survey. The data are used mainly to update travel demand models and did not make major news. But the survey, which involved a huge sample of more than 42,000 households in 2012, depicts some interesting patterns in mode choice.

The 2012 survey shows that the average California household made about 25 percent fewer trips by automobile than it did in 2001, and 65 to 75 percent more trips by walking, biking, and public transit. Those changes mean the shares of the three non-auto modes doubled. Figure 1 shows mode shares from the two surveys.

Figure 1. California mode shares. Source: California Household Surveys, Caltrans.

Figure 1. California mode shares. Source: California Household Surveys, Caltrans.

The mode shifts are so significant that they suggest a methodological change in the surveys might be responsible. For example, the new study incorporated data from GPS devices worn by more than 8,000 people to account for misreporting in travel diaries, in addition to in-vehicle GPS devices, which were used in both studies. However, a close examination of the two studies suggests these mode shifts are quite plausible.

While the new survey better accounted for non-auto trips that may contribute to the increase in those modes, the major factor in the mode shift seems to be a decline in driving, a mode that was measured with GPS in both surveys. According to the surveys, household vehicle trips in California decreased by more than one-third, even as the number of households increased by 9 percent—a finding that is consistent with other data showing a drop in per capita and per household vehicle-miles traveled over the past decade.

The modal shifts are in line with goals outlined in Caltrans’ Smart Mobility Framework, such as reducing per capita VMT, as well as those of the state’s landmark climate legislation, A.B. 32 and S.B. 375.

“This increasing interest in many transportation choices is another reason why we are on the path to more sustainability in California,” California State Transportation Agency Secretary Brian Kelly said. “Caltrans will continue improving the state’s transportation system to help ensure Californians have many viable choices for how to travel.”

Data from the recent California household travel survey and other large-scale regional travel surveys are available from the National Renewable Energy Laboratory.

Chris McCahill is a Senior Associate at SSTI.