On the social desirability of urban rail transit systems, Journal of Urban Economics Volume 62, Issue 2, September 2007, Pages 362-382
Despite a decline in its mode share, investment to build new urban rail transit systems and extend old ones continues. We estimate the contribution of each U.S. urban rail operation to social welfare based on the demand for and cost of its service. We find that with the exception of BART in the San Francisco Bay area, every system actually reduces welfare and is unable to become socially desirable even with optimal pricing or physical restructuring of its network. We conclude rail’s social cost is unlikely to abate because it enjoys powerful political support from planners, civic boosters, and policymakers.
When I have a little time, I will produce a more comprehensive bibliography. My reading of (a fairly extensive) literature is that rail makes sense only in the densest places, such as New York, Boston, Tokyo, Paris, London, Seoul, etc. I would build metros in Indian cities that do not have them. But I have never seen a socially compelling case for light rail.
BTW, I personally love rail. One of the best things about living in Bethesda and working in Foggy Bottom is that I almost never drive to work. Metro is great for me. But should low income taxpayers in Kansas (or Frederick, Maryland, for that matter) be paying for a professor to be able to read in comfort on the way to work in Washington?