A track-laying shuttle car

DURING THE PAST quarter century the introduction of mechanical mining has revolutionized the coal industry. As the revolution progressed, a bottleneck developed in the operation behind the loading machine. Transportation schemes in use 20 years ago could not move the coal away from the loader fast enough. In 1935 the idea was conceived of using rubber-tired tractor-trailer units to maintain a steady flow of coal from the loader to the secondary track system. These units proved efficient for gathering the coal, but occupied too much space. About 1939 a single-unit self-propelled shuttle car, basically the type being used today, was developed.