My colleague Jeff Taylor writes in Reason Express:
It is almost a running joke that public mass transit systems across the county, particularly ones with a light rail component, lament that they would be a much better deal for taxpayers if only more people would ride them. Get ridership up and great things will happen for the community: The air will be cleaner, the kids smarter, and life just better overall. The corollary is that, absent those riders, it is just going to cost more money upfront from taxpayers to run the systems.
And then along comes D.C. Metro to blow that all to hell. Metro officials lament that their system is beset by too many riders and that funding must increase to cope with them all. And this is a $10 billion modern system, the oldest parts of which are only a few decades old, one that has been lavished with federal subsidies since its inception, one that has benefited from a good design and the necessary development density to make light rail function. And yet Metro wants its own dedicated regional sales tax to keep the system running.
Cities contemplating pumping tens or hundreds of millions into light rail systems need to ask themselves how they would avoid the problems Metro now grapples with. Absent a good answer, maybe the best idea is to pass on the projects and avoid the whole too few/too many dilemma.