sporvidde

Sporvidde, or track gauge, is the distance between the inner sides of the two rails on a railway track. It is a fundamental parameter of rail infrastructure and influences the design of rolling stock, track stability, and interoperability between rail networks. Gauge is typically measured in millimetres, though some historical contexts use inches.

The most widely used gauge worldwide is standard gauge, 1,435 mm (4 ft 8 1/2 in). Widespread variations are broadly categorized as broad gauges, metre gauges, and narrow gauges. Broad gauges generally exceed standard gauge and include values such as 1,520 mm (used in parts of Russia and Finland) and 1,668 mm (Iberian gauge used in Spain and Portugal). Metre gauge is 1,000 mm, while narrow gauges can range from about 600 to 900 mm and are common in light rails, mountainous areas, or industrial lines. India, for example, uses a broad gauge of 1,676 mm, while several former Soviet states use 1,520 mm.

Gauge differences affect interoperability; trains cannot run legally on tracks with a different gauge without mechanisms such as gauge-changing technology, dual-gauge tracks, or transshipment. Historical factors, terrain, and rolling stock dimensions shaped regional gauge choices, leading to a patchwork of gauges that continues to pose logistical challenges at borders. Modern rail planning frequently prioritizes standardization, border compatibility, and options for gauge-changing solutions where cross-border traffic is important.