Mixedgauge

Mixed gauge, or mixed-gauge track, refers to railway infrastructure that accommodates more than one rail gauge on the same route or facility. This can be achieved by adding extra rails or by compatible wheel and bogie designs, allowing rolling stock built to different gauges to operate without changing trains. The goal is interoperability and flexibility in systems where gauges differ due to historical, political, or economic reasons.

Historically, mixed gauge emerged during early railway expansion when rival networks used incompatible gauges. A notable example is Britain in the 19th century, where broad gauge and standard gauge ran on the same corridors using three-rail configurations or adjustable track elements. Mixed gauge enabled interchange and gradual conversion from one gauge to another. Over time, many networks standardized on a single gauge, reducing or eliminating dedicated mixed-gauge sections. Nonetheless, the concept persisted in regions where rapid gauge conversion was not feasible or where legacy lines remained in service.

In modern practice, mixed gauge remains relevant in limited contexts. Some lines in India historically used dual or mixed gauge to carry both metre gauge and broad gauge traffic, with three rails enabling compatibility during gradual gauge program accelerations. Elsewhere, gauge-changing technologies and dual- or multi-gauge solutions have been deployed to bridge gauge differences without full line conversion, notably in certain European and Latin American experiments and in some high-speed and rolling-stock projects that require interoperability with adjacent gauge networks.

Technical considerations include track geometry, switch design, and maintenance challenges. Mixed-gauge systems require careful alignment and robust safety protocols to manage trains of different widths and wheel configurations, and they are generally more complex and costly than single-gauge installations. As networks standardize, the prevalence of mixed gauge has declined, though it remains a relevant concept in heritage lines, transitional projects, and specialized interoperability efforts.