Some railways employ radio control of locomotives to reduce the manning required for shunting. This allows a locomotive to be moved from the ground and assists with safety as well as reducing the time required for coupling and uncoupling. Radio control is also employed for long and heavy freight trains where locomotives are provided at the front and rear of trains to assist with power and braking. This allows a single driver in the leading cab to control all other locomotives without the need to provide control wiring throughout the train. In any case, on very long trains the voltage drop for hard wired control signals would make their use impossible. For braking, air brakes are standard. The propagation rate for a long train would be excessive using a brake pipe controlled only from the front. Radio control allows the pipe to be controlled from several points on the train and speed up operation.