Trackleveys

Trackleveys, or gauge, is the distance between the inner faces of the two rails on a railway track. It defines the maximum width of wheel treads and the set of rolling stock that can run on a line. The gauge is typically measured as the distance between the inner surfaces of the rails at the top, and is usually expressed in millimeters or inches. Trackleveys directly affects compatibility between locomotives, cars, and infrastructure, and is a fundamental parameter for railway design and operation.

Globally, several gauge categories are in use. The standard gauge, 1,435 mm (56 1/2 in), is the most widespread and forms the basis for much of the modern network in Europe, the Americas, and parts of Asia. Broad gauges range from about 1,520 to 1,524 mm (59 3/4 to 60 in) and are used in Russia, Finland, the Baltic region, and some other areas. Iberian gauge, at 1,668 mm (65 3/4 in), is used in Spain and Portugal. Metre gauge is 1,000 mm (39 3/8 in) and remains common in parts of Africa, Asia, and South America. Narrow gauges below 1,000 mm are also used, for example 1,067 mm (3 ft 6 in) in Japan and several countries in other regions, as well as many 750–900 mm industrial and regional lines. Gauge choices often reflect historical development, terrain, and cost considerations.

Implications of trackleveys include rolling stock design, axle and wheelset manufacture, and interoperability. Differences in gauge hinder cross-border travel and require transshipment, bogie exchange, or the use of dual- or gauge-changing systems. In modern networks, standardization promotes interoperability for high-speed and international services, while legacy or regional networks may retain multiple gauges for logistical or economic reasons.