GM first replaced trolleys with free-roaming buses, eliminating the need for tracks embedded in the street and clearing the way for cars. As dramatized in a 1996 PBS docudrama, Taken for a Ride, Alfred P. Sloan, GM’s president at the time, said, “We’ve got 90 percent of the market out there that we can…turn into automobile users. If we can eliminate the rail alternatives, we will create a new market for our cars.” And they did just that, with the help of GM subsidiaries Yellow Coach and Greyhound Bus. Sloan predicted that the jolting rides of buses would soon lead people to not want them and to buy GM’s cars instead.
from The Conservation Report quoting from Larry West at About.com and The Straight Dope.