Economists on Rail
This is a long, detailed report on the economic impacts of rail transit projects. The focus of this article is the cost effectiveness of rail transit. For example:
Rail transit does divert some traffic off the roads, but rail systems are so expensive to build and operate and transport such a small share of travelers that they can be justified on cost-benefit grounds in only a few U.S. cities.
This the real issue, since rail is so expensive it is rarely cost effective. This is a major consideration here on Oahu where rail will not carry enough people to justify its exorbitant cost.
The whole report (pdf) is here.