Guard rail (rail transport)

In rail transport, guard rails or check rails are rails used in the construction of the track, placed parallel to regular running rail to keep the wheels of rolling stock in alignment to prevent derailment. They are generally used along areas of restricted clearance, such as a bridge, trestle, tunnel, or level crossing. They also help to minimize damage to the structure and allow easier post-accident cleanup.
As per UK/Australian terminology, guard rails and check rails perform distinctly different functions. However, US terminology refers to both types as guard rails, despite their differing functions.
Check rails are located relatively close to the corresponding running rail, such that the wheels of rail vehicles regularly contact the side of the check rail. Such is contact is essential for the function of the check rail, i.e. to prevent derailment of opposing wheels when passing through sharp curves or switches. The distance from the contact face of the check rail to the opposing running rail is critical and referred to as the check gauge effectiveness.

History

Although guard rails in some form have been used as long as there have been trains, the precursor of the guard rails in use today was detailed in, filed in 1893 by Gorham B. Ames, based in Laconia, New Hampshire, US.

Applications

Bridges

Guard rails are an essential component of railroad bridges. Their presence prevents a derailed train from striking and damaging bridge components, or deviating from the track enough to leave the tracks entirely and roll over or fall.

Sharp curves

On sharp curves, check rails may be placed inside the inner rail, where they engage the back of the flange of the wheel on that side.

Switches

Check rails may be incorporated in switches, where they serve to prevent derailments caused by a train's wheels passing through the wrong side of the frog. Check rails in this case are typically bolted to the traffic rails on each end, with a clamp placed towards the center to prevent movement.