a direct current motor controlling apparatus determines the operational speed of one or more direct current motors such as traction motors propelling a passenger vehicle along a track . the speed of the motor is established by changing the on and off conduction ratio or duty - cycle relationship of a switch device to determine the field current and the armature voltage of that motor . the present apparatus utilizes solid - state switch devices to determine the mode of operation of the motor control apparatus which solid - state switch devices are more reliable and more simple in operation and less expensive to maintain .