The Gullibility Multiplier

A recent report published by the Transit Cooperative Research Program (TCRP) concluded that transit reduces greenhouse gas emissions. How can this be when (as the Antiplanner has shown) data published by the Departments of Transportation and Energy show that transit emits as much or more greenhouse gases per passenger mile as the average car?

Easy! The authors of the TCRP paper, using the same data I used, found that transit emitted as much or more greenhouse gases per passenger mile as the average car. They also admitted that without transit, only “33 percent of transit passenger miles would otherwise be replaced by personal vehicle miles,” which means transit is three times worse than driving.

However, they then introduce two magic numbers that, when combined with transit’s real emissions, allow them to make it appear that transit is saving huge amounts of total emissions. The first magic number is called the land use efficiency multiplier. It assumes spending money on transit would lead to land-use changes that would in turn lead people to drive less, including people who don’t ride transit. The second magic number is called the transit efficiency multiplier, and it assumes that people who ride transit, say, 100 miles a week avoid several hundred miles of weekly driving.

Based on these two magic numbers, the paper concludes that each million passenger-mile carried by transit saves 6 to 13 vehicle miles of driving. Yet these numbers are not supported by real world experience. If the paper is correct, then urban areas that spent more on transit in the last few decades would have significantly reduced per capita driving. Instead, comparing per capita driving in 1989 with 2019, there is no clear relationship between transit spending and per capita driving.

Dallas-Ft. Worth has spent $11 billion (in 2020 dollars) on transit capital improvements since 1992 (the earliest year for which data are available). Per capita driving there increased by 12 percent. Denver also spent $11 billion on transit capital improvements and saw per capita driving grow by 51 percent. Salt Lake City spent $6.2 billion; per capita driving grew 42 percent.

There were a few cases where more money meant less driving, but only slightly less. Seattle, for example, spent $26 billion on transit; per capita driving declined 3 percent. But Portland spent $6.4 billion and per capita driving grew by 10 percent. If it takes an extra $20 billion to reduce driving by 3 percent, it probably isn’t worth it.

There may be a land-use effect on per capita driving. The New York urban area saw only 60 percent as much per capita driving in 2019 as Dallas or Houston. But that land-use effect is not a result of transit, as implied by the TCRP study. Plus, for what it’s worth, per capita driving in New York grew by 13 percent between 1989 and 2019.

To the extent that there are any land-use or transit effects, the TCRP study has exaggerated them by failing to account for self-selection bias. In other words, people who want to drive less will tend to live in areas that are denser and have better transit. But that doesn’t mean that moving a family of four from the suburbs into an inner-city condominium will automatically reduce their driving by four or five times, as the TCRP paper assumes. As UC Irvine economist David Brownstone concluded, after accounting for self-selection bias, “the size of this link” between urban form and driving “is too small to be useful” in saving energy or reducing greenhouse gas emissions.

Introducing magic numbers that cannot be supported by real-world data turns the TCRP paper into junk science. This is compounded by the paper completely ignoring the possibility of self-selection bias in its numbers even though Brownstone and others raised this issue well over a decade ago.