Washington Post Wary of Dulles Rail Cost

The Washington Post's editorial page has been a major supporter of plans to build a 23-mile extension of Metrorail to Dulles International Airport. But now the escalating estimates of its cost - $2.4 billion for the first phase, up from a previous estimate of $1.5 billion - has curbed its enthusiasm.

The paper's editorial today wonders if it's becoming a "vanity project" for its powerful backers and urges planners to look at all the options - including road improvements and a less-costly bus rapid transit system.

I'm not sure what line was crossed here by the higher cost estimates - previous studies had already declared that BRT was less costly than rail. What does BRT lack that made transportation planners and these 'powerful friends' willing to leave those savings behind?