sorry, Jack the Sailor I dont have a link, Ive read it in Fast Food Nation (by Eric Schlosser) which covers the rise of agri-business over the last century. One chapter is devoted to this topic, but the idea that the big automakers went around and bought up all the tram companies and closed them down in the 30's and 40's to encourage/force people to buy cars is well known. Im sure a quick search can lead to more info.
Petr