Multiheaded trains
From OpenTTD
Multiheaded trains are a way to increase the speed and capacity of trains. Multiple engines are added to the same train to allow better climbing of hills, acceleration, and greater capacity for cargo
With the "Multiheaded Trains" patch turned on, train engines are treated as cars and can be moved from one train entity to another. Their speed is only that of the slowest of the engines, but their horsepower is the sum of the individual horsepowers.
Note that this differs from TTDPatch Multihead handling in several ways: You no-longer have to create the engine as a train car by holding ctrl. Instead you simply drag the second engine onto the train it will join. Also, second engines can only subtract from the total speed, not add to it.
Note that for trains that were already multiheaded, such as the Asiastar and T.I.M. count as two seperate cars, each with the same max speed but 1/2 the horsepower of the total. Only the first head can be used to create a route, the second is only a car and must be attached to another train entity.
