Guard rail (rail transport)

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.

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 U.S. patent 522,038, filed in 1893 by Gorham B. Ames, based in Laconia, New Hampshire, US.

[1] The object of the guard rail is to prevent a derailed truck from getting far enough off the track to strike any portion of the girder, or from becoming twisted so as to lead to further derailment ... guard rails are requisite, so arranged as to bring a derailed truck nearly back to its proper position and guide it across the bridge without allowing it to deviate more than a few inches from the rails.

[3] Guard 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 (the point where the straight and diverging rails cross).