The Speedwagon was a fast station wagon of the 1940's made by Ransom E. Olds (I don't know what the E stands for). Mr. Olds started two car companies, Oldsmobile and REO. Oldsmobile was later purchased by GM. REO became extinct a long time ago. Obviously, Oldsmobile is now just a part of automotive history as well.
Think of the REO Speedwagon as the Dodge Magnum SRT8 of the 1940's. I seriously believe the band was named after the car (also with Pantera).