Abstract:This report is one of a series of research documents produced by an ongoing study of individuals' mobility and attitudes toward travel. The data are obtained from 1,358 residents of three San Francisco Bay Area neighborhoods, who work either part- or full-time and commute.

The key premise of this research is as follows: although the demand for travel is, for the most part, derived from the demand to engage in spatially-separated activities (as conventional wisdom holds), travel itself has an intrinsically positive utility that contributes to the demand for it. That affinity for travel itself (partially operationalized in this study through the Travel Liking variables) varies by person, mode, and purpose of travel. The goals of this research are to better understand causes and effects of that affinity for travel. The key variables used in the study can be grouped into 11 categories: Objective Mobility, Subjective Mobility, Relative Desired Mobility, Travel Liking, Attitudes, Personality, Lifestyle, Excess Travel, Mobility Constraints, Travel Modifiers and Demographics.

Ultimately, structural equations models will be developed to properly account for the inherent endogeneity of some of these variables. As initial building blocks toward that ultimate goal, however, single-equation models are being developed for the major types of endogenous variables in the system. This report focuses on modeling Subjective Mobility; companion reports focus on Objective Mobility and Relative Desired Mobility.

Linear regression models were developed for 10 dependent Subjective Mobility variables, representing the qualitative assessment of various kinds of travel on a five-point ordinal scale from "none" to "a lot". For short-distance travel the categories modeled include Subjective Mobility for travel overall, the commute to work/school, for work/school-related reasons, for entertainment/recreation/social reasons, and by personal vehicle. For long-distance travel, we modeled Subjective Mobility for travel overall, for work/school-related reasons, for entertainment/recreation/social purposes, by personal vehicle and by airplane.

Subjective Mobility is the result of a process though which people filter their actual amounts of travel. Actual mobility can be measured in terms of frequency of trips, average trip distance, total distance traveled, and total travel time. One main purpose of this study is to understand how these various measures are woven together to construct people's subjective assessments of their actual mobility. A second main purpose is to identify other factors that magnify or diminish individuals' subjective assessments of their mobility, after controlling for their objective levels of mobility.

Understanding people's perception of their own mobility provides new insight that may improve our models of objective travel behavior. If we know that one kind of person views 100 km/week as a "little" travel while another views it as a "lot", we might expect the former type of person to be inclined to maintain or even increase her travel (and hence, for example, not to be receptive to policies intended to motivate travel reduction, all else equal), while the latter type may be more inclined to decrease it. It then becomes relevant to characterize the people that tend to exaggerate their perceptions of Objective Mobility, compared to those who tend to minimize them.