Transit and Carpool Commuting and Household Vehicle Trip Making: Panel Data Analysis

Abstract

Most of the evaluation of commute trip reduction programs centers on the effect on reducing driveway trips at the work site. Little has been done to explore the effects of such programs on overall trip making. This work is meant to help understand this relationship by determining the association between transit and carpool commuting and overall household vehicle trip making. Household activity models have indicated that an individual's travel decisions influence (and are influenced by) the decisions of other household members. It is thus postulated that one household member's choice of transit or carpool for the morning trip to work will affect the mode choices of the other household members. In addition, the choice of mode to work will affect the individual's mode choices for trips other than the morning trip to work. The analysis uses the first four waves of the Puget Sound Transportation Panel survey to construct linear econometric longitudinal trip generation models (random effects models). The results of the modeling indicate that one household member's mode choice to work does affect overall household vehicle travel. Compared with driving alone to work, if one household member chooses transit to work, overall household vehicle trips are reduced (on average). Carpooling by one household member is associated with little change in overall household travel, with average daily household vehicle trips ranging between one trip fewer and one trip greater than households where each driver in the household drives to work in a separate, single-occupant vehicle. The analysis strengthens the associations to imply causal links. The model results suggest that an improved understanding of interactions among household members is necessary to define strategies in support of commute trip reduction policies to better meet air quality and congestion-management goals.

Managed lane choices by carpools comprised of family members compared to non-family members

“…Most research has focused on how carpooling mode share changes with time, fuel costs, socio-economic characteristics like income, economic growth, availability of jobs, etc. (Bard, 1997;Doherty et al, 2002;Ferguson, 1997). A great deal of the research done on carpool mode share has used the National Household Travel Survey (NHTS) dataset which is limited to socio-economic and demographic variables.…”

Can Carpooling Clear the Road and Clean the Air?

“…Brownstone and Golob (1992) address Teal’s concern by building a model that predicts which kinds of incentives favor ride sharing: HOV lanes, guaranteed rides home, preferential parking, subsidies, or an amorphous category of other incentives. Bard (1997) looks at how carpooling decreases the total number of trips taken by a household, but does not extend this to traffic outcomes or welfare calculations. Plotz, Konduri, and Pendyala (2010) put bounds on how many carpools were formed because of HOV lanes.…”

To What Extent Can High-Occupancy Vehicle Lanes Reduce Vehicle Trips and Congestion?

“…It is believed that, with provision of HOV lanes in congested corridors, some solo drivers will form rideshare partnerships with family, friends, or coworkers to save travel time. Household activity studies have suggested that one household member's travel decision will influence the decisions of others in the same household and vice versa (2). Thus, if one person chooses to carpool, the likelihood that another household member will do so increases.…”