If a railway track runs over a bridge which has expansion joints that move more than a few millimeters, the track must be able to compensate this longer expansion or contraction. On the other hand, the track must always provide a continuous surface for the wheels traveling over it. These conflicting requirements are served by special expansion joints, where two rails glide along with each other at a very acute angle during expansion or contraction. They are typically seen near one or both ends of large steel bridges. Such an expansion joint looks somewhat like the tongue of a railroad switch, but with a different purpose and operation.