check-rail

from The Century Dictionary.

• noun A guard-rail; an extra rail on the inner side of the inner rail of a railway curve, so laid as to leave sufficient room for the flanges of the wheels to pass freely between the heads of the two rails.
• noun In railroads, a contrivance at the crossing from one line of rails to another, or at a siding, for allowing trains to run on to or move into the other line or siding.