The Fort Bend Toll Road Authority in Texas recently completed a four-lane freeway at a cost of less than $10 million per mile, or $2.4 million per lane mile. By comparison, the average streetcar line being considered for federal funding by the Federal Transit Administration in 2015 costs $46 million per mile; the average light-rail line costs $176 million per mile; and the average heavy-rail line costs $441 million per mile. Because most commuter-rail lines use existing tracks, the average cost is just $36 million per mile, but that’s still far more than highway costs.
Four-lane highways can cost more than $10 million a mile, of course. Boston’s Big Dig project cost $14.6 billion for 161 lane miles, or about $90 million per lane mile. But similar subterranean rail transit projects can make that seem positively cheap. New York City, for example, is building subways that cost $2.2 billion per mile, while Seattle is building a 3.1-mile light-rail line that is costing $628 million per mile.