The Transport Politic runs down recent coverage of BRT as a false argument against rail. That argument simplifies city mobility too much, according to this post.
"What is clear is that for the majority of American cities - excluding only a few in the Northeast - buses will remain the predominant mode of public transit for most riders, even after major expansions in train networks planned for cities from Charlotte to Phoenix. So even cities that choose to invest in rail projects must also spend on the improvement of their bus lines.
Nor is the difference in costs between rail lines and BRT nearly as great as some would argue. The Journal article quotes Dennis Hinebaugh, head of a transportation center at the University of South Florida, saying "You can build up to 10 BRT lines for the cost of one light-rail line." That might be true if you're comparing a train operating entirely in its own right-of-way with a bus running in a lane painted on the street. But a streetcar is probably cheaper than a busway. Just ask Hartford, whose busway project will cost $60 million a mile to build."