Arizona transportation researcher John Semmons has an excellent oped on the inefficiency of light rail transit worth reading. The oped was published in the Oregon Statesman Journal and distributed by the Independent Institute in Oakland.
Critics of LRT point out that it is not theoretical capacity that is crucial, but actual ridership and the cost incurred to garner this ridership. National figures indicate that on average, LRT carries about 5,000 people per track-mile per day, while urban freeways carry over 20,000 per lane-mile per day. So, in actual numbers of people served, freeways seem to handle over four times as much traffic as LRT does.
Also, Semmens points to an excellent 2006 study by the Arizona Transportation Research Center that analyzed freeway, light rail and alternative transportation projects based on cost effectiveness: Multimodal Optimizaiton of Freeway Corridors.