This study explores factors contributing to the decrease in biking and walking in California over the period from 2012 to 2017, as observed in comparisons of the most recent California Household Travel Survey (CHTS) and the California add-on sample of the National Household Travel Survey (NHTS), respectively. Previous analysis conducted for Caltrans shows that these changes likely represent real shifts in the use of active travel modes; the observed changes cannot be attributed to methodological differences in the survey and data processing on its own. The changes can be attributed to changes attributed therefore to other, real factors. This study will consider these factors and investigate their impact on the change in mode shares from the 2012 CHTS to the 2017 CHTS through descriptive analysis as well as statistical models. The researchers will explore a number of mode share outcomes in this analysis. These include the share of trips made by walking and biking, the share of commuters who use walk or bike as their usual mode to work or school, and those survey participants who have biked or walked at all in the past week. Each of these measures of mode use highlights different aspects of travel that should be considered with respect to walking and biking targets and strategies.