Monday, May 20, 2013

How to interpret high transit ridership of TOD residents

Living within a walkable distance of a transit stop has been shown to significantly increase the likelihood that an individual will ride transit. Studies in the Bay Area and Washington DC found that residents within a half-mile of a rail stop were three to five times more likely to commute by rail (1). Public policy has sought to capitalize on this ridership bonus through a range of strategies to increase transit-oriented development (TOD), such as subsidizing or financing development near stations, rezoning, or lowering transportation impact fees.

Opponents of rail transit and TOD have claimed that people who live within a TOD area choose to use transit not because it is more economically efficient, but because they prefer a less car-dependent lifestyle (2). The research literature calls this phenomenon “self-selection bias,” and acknowledges that it is an important factor in the higher probability of riding transit for TOD residents. However, opponents of TOD use the findings to claim that governments should not attempt to change travel behavior because people who desire to use transit will self-select to live near stations anyway.

Two problems exist with this conclusion. First, it glosses over the significant role of land use patterns and the built environment in influencing travel mode decisions. A review of empirical research on the topic found that every study that attempted to control for self-selection still found that land use patterns remained significant predictors of transit ridership (3). For example, a study of Bay Area TODs found that 40% of the ridership bonus could be attributed to self-selection; so lifestyle preference does not explain all of the increased ridership TODs generate (4).

Second, we can accept the importance of self-selection, but still conclude with different policy recommendations. Real estate markets are imperfect and many factors can disrupt the market from matching supply with demand. The strong demand for transit-oriented living, and the relatively short supply of this type of housing, suggests that the real estate market is not functioning optimally, and policy interventions are needed to stimulate development in TOD areas. For example, zoning policy may need to change to respond to the market demand coming from smaller households with less cars. Location efficient mortgages can increase loan eligibility for those living near transit by recognizing the personal cost savings of driving less (5). Self-selection results in increased ridership of people living near transit, but does not imply that real estate markets are providing the residential mobility needed for self-selection to happen freely.

(1) Cervero, R. (2006). Transit oriented development’s ridership bonus: a product of self-selection and public policies.
(2) O’Toole, R. (2010). Urban Transit. Downsizing the Federal Government. Cato Institute. Retrieved at:
(3) Cao, X., Mokhtarian, P. L., & Handy, S. L. (2009). Examining the impacts of residential self‐selection on travel behaviour: a focus on empirical findings. Transport Reviews, 29(3), 359-395.
(4) Cervero (2006), p. 25
(5) Cervero (2006), p. 27

Edited by Kelly Sellers

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