One common argument against boosting public transportation is that buses, trains and subway systems “don’t pay for themselves.” Roads, we’re told, are bankrolled by drivers, via gas taxes. Subway systems, by contrast, aren’t self-sufficient and usually need additional funds on top of whatever they collect through fares. (Boston’s subway system, for instance, collects just 25 percent of its revenues through fares; the rest comes from a state sales tax and other local funds.)

But there are two counterarguments here. The first is that roads don’t always pay for themselves (see this report, or ask the Texas DOT). And the second is that public transit doesn’t just benefit the people who ride the buses or subways. It also benefits drivers, by reducing overall congestion. Aaron Renn wades through the Texas Transportation Institute’s recent report on urban mobility and finds data on how much congestion is actually reduced by transit systems in 10 different U.S. cities (figures are in millions of dollars):