the rails are supported by cross pieces set at regular intervals (called sleepers or ties), which spread the high pressure load imposed by the train wheels into the ground. they also maintain the rails at a fixed distance apart (called the gauge). ties are usually made from either wood or concrete. these often rest on ballast, which is a name for very small pieces of broken up rock that are packed together and keep the railway tracks in place. tracks are often made better by ballast tampers.