TransForm, a smart-growth group in Oakland, has analyzed California’s household travel survey data and made what it thinks is an important discovery: poor people drive less than rich people. Moreover, poor people especially drive less than rich people if the poor live in a high-density development served by frequent transit (that is, a transit-oriented development or TOD).
According to TransForm’s report, poor households who live in TODs drive only half as much as poor households who live away from TODs, while rich households who live in TODs drive about two-thirds as much as rich households who don’t live near TODs (see figure 1 on page 7).
Based on this, TransForm proposes that California build lots of “affordable housing” in the TODs, then herd encourage poor people to live in the TODs. Apparently, TransForm’s thinking is that moving poor people into TODs will have the greatest effect on driving, energy consumption, and greenhouse gas emissions. Putting “more affordable homes near transit … would be a powerful and durable GHG reduction strategy,” says TransForm (emphasis in the original).
Unfortunately, TransForm’s proposal is grounded on a seriously flawed analysis and morally questionable reasoning. First, TransForm has committed a simple arithmetic error when it concludes that the best greenhouse-gas reduction strategy would be to focus on low-income people. Though the data show rich people in TODs drive only a third less than rich people away from TODs, the rich drive so much more than the poor that the greatest impact would come from herding the rich into the TODs.
According to TransForm’s data, poor households in TODs drive about 21 fewer miles per day than poor households away from TODs. But rich people in TODs drive 29 miles less than rich people away from TODs. Thus, if you believe TransForm’s numbers, the best greenhouse-gas reduction strategy would be to coerce encourage rich people to live in TODs.
However, I don’t believe TransForm’s numbers because TransForm has made the classic error of ignoring self-selection. That is, people of all incomes who want to drive less are more likely to live in TOD-like places, while people who want to drive more are more likely to live away from TOD-like places (which are typically the most congested and least auto-friendly).
Note that all of TransForm’s numbers measure miles of driving and other factors per household, not per person. Households in TODs tend to have no children, while households with children are far more likely to live away from TODs. It’s a mistake to think that, because people who want to drive less tend to live in TODs, getting people who want to drive more to live in TODs will lead them to drive much less than they do. As economist David Brownstone concludes, after taking self-selection into account, the effect of urban form on driving is “too small to be useful” in reducing greenhouse gas emissions.
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