Wikipedia's "Light rail" (http://en.wikipedia.org/wiki/Light_rail) article has some interesting numbers on the cost of light-rail construction: Over the U.S. as a whole, excluding Seattle, new light rail construction costs average about $35 million per mile. By comparison, a freeway lane expansion typically costs $20 million per lane mile for two directions.
Why couldn't you use the elevated track strategy these guys developed with modified light rail cars? The light rail cars would also benefit from lighter construction.
