Rail Diesel Cars are designed for bidirectional operation.  RDCs have control cabs, horns and headlights on each end which allow the car to operate in either direction without turning around.  This is especially useful on remote lines which lack turntables or Y track*.

Here BC-30 idles in Vancouver, British Columbia.  Passenger service on the line was discontinued two weeks after this photograph was taken and BC-30 was sold to a railroad in New Hampshire.
 
*A Y track allows a train to change directions using a three-point turn.