Dana Hedgpeth, “Wary eyes on Dulles rail project’s bottom line,” Washington Post, 1 October 2011.

The original Metro system was estimated to cost $2.5 billion in 1969, but it came in at $3.8 billion — not counting inflation, according to Zachary M. Schrag, associate professor of history at George Mason University and author of “The Great Society Subway,” a history of Metro.

“It would be somewhat surprising for a major rail transit project to be completed on budget,” Schrag said. “Most major projects of any kind go over budget, that includes road projects, weapons systems, space programs, stadiums.”

Typically, overruns hit because it is hard to predict the cost of such expenses as materials and the relocation of utilities in a construction area, Schrag said. “It is kind of a vicious spiral where people low-ball the estimates to get their project approved,” he said.