The mean temperatures of a thyristor-driven traction motel, while operating on a very busy railway-line, have been measured. The factors affecting the attained temperatures are the loaning imposed on the motor, its electric-current input, the train’s speed versus time pattern, the dwell times at the stations on route, and the driving practice. It is essential to timetable the operations of the train so as not to overload the traction motor, and thereby avoid its overheating and rapid subsequent breakdown. Design improvements are suggested.