The Caterpillar DT-1 Street Tractor moved railroad cars around Baltimore’s Inner Harbor.

Given the tight curves and narrow streets, the Baltimore and Ohio Railroad found it advantageous to use special "street tractors" instead of locomotives when serving the Fells Point neighborhood. Unlike a locomotive, you can drive it anywhere if you're not towing something. You can also drive around the block if you need to get on the other end of a car to shove it into a facing point siding. The downside of these is that it only works where the tracks are embedded in pavement.