fourrail

Fourrail refers to a type of railway track configuration that utilizes four rails instead of the more common two. This arrangement is typically employed to accommodate two different track gauges on the same physical right-of-way. One common application is in areas where standard gauge (1,435 mm or 4 ft 8 1⁄2 in) and broad gauge (such as 1,676 mm or 5 ft 6 in) railways converge or intersect.

In a four-rail system, two inner rails are set at one gauge, and two outer rails are set at a different gauge. Trains operating on the narrower gauge run on the inner pair of rails, while trains on the wider gauge run on the outer pair. This allows for seamless transition and operation of rolling stock from both systems without the need for separate tracks or costly gauge conversion.

The implementation of four-rail track can simplify operations at junctions and terminals, allowing trains of different gauges to access the same platforms or sidings. However, it also introduces complexities in track maintenance, signaling, and switch design. The precise positioning of the rails and the switching mechanisms must be meticulously engineered to ensure safe and reliable operation for both types of trains. Historically, four-rail track has been used in various countries to facilitate the integration of different railway networks.