A tie plate is a thick steel panel that sits between the rails and ties, or sleepers, on a standard railroad track. Railroad tie plates are generally tapered at either end to improve stability and reduce torsion and twisting along the rails. Rails installed with tie plates are better able to maintain their position, which helps to standardize the width, or gauge, of the track along its length. Engineers and builders use rail tie plates to extend the longevity of a new track installation, and to maximize safety for passengers and railway workers.
In traditional rail construction, workers lay a bed of gravel or loose stone. They top the stone with short wooden beams, or ties, which act as a support for the steel rails. A steel spike is driven through a flange along the base of the rail to fasten it to each tie.
Since the early 20th century, many railroad engineers have specified the use of tie plates on new lengths of track. Instead of fastening the rail directly to the tie, the spike passes through the tie plate first, then into the end of each tie. While these plates are still found on railroads that use wooden ties, the use of concrete or composite ties in modern construction has reduced the need for tie plates.
Each rail tie plate features either a single- or double-shoulder construction. On a double-shoulder unit, the tapered ends of the plate are raised to create a sunken bed in the middle, which must be sized to match the width of the rail. The rail fits snugly between the two shoulders, which increases support and stability on either side of the rail. Single-shoulder tie plates contain only one raised edge, which fits against one side of the rail. These versatile units allow workers to use the same plates on rails of any size.
Tie plates help to evenly distribute the weight of the train and cargo over a larger portion of each tie. This reduces friction between the rails and ties, and helps the wooden ties last longer than they otherwise would. It also helps the metal rails wear more evenly, and allows them to maintain a smoother, more uniform surface. Because each tie plate adds an extra step to the construction process, railroads with plates take longer to build, and often come with higher labor and material costs. Tracks constructed without wooden ties generally don't require tie plates.