High-speed rail (HSR) is a type of rail transport network utilizing trains that run significantly faster than those of traditional rail, using an integrated system of specialized rolling stock and dedicated tracks. While there is no single definition or standard that applies worldwide, lines built to handle speeds of at least 250 km/h (155 mph) or upgraded lines of at least 200 km/h (125 mph) are generally considered to be high-speed.
The first high-speed rail system, the Tōkaidō Shinkansen, began operations in Honshu, Japan, in 1964. Due to the streamlined spitzer-shaped nose cone of the trains, the system also became known by its English nickname bullet train. Japan's example was followed by several European countries, initially in Italy with the Direttissima line, followed shortly thereafter by France, Germany, and Spain. Today, much of Europe has an extensive network with numerous international connections. Construction since the 21st century has led to China taking a leading role in high-speed rail. As of 2023, China's HSR network accounted for over two-thirds of the world's total.
In addition to these, many other countries have developed high-speed rail infrastructure to connect major cities, including: Austria, Belgium, Denmark, Finland, Indonesia, Morocco, the Netherlands, Norway, Poland, Portugal, Russia, Saudi Arabia, Serbia, South Korea, Sweden, Switzerland, Taiwan, Turkey, the United Kingdom, the United States, and Uzbekistan. Only in continental Europe and Asia does high-speed rail cross international borders.
High-speed trains mostly operate on standard gauge tracks of continuously welded rail on grade-separated rights of way with large radii. However, certain regions with wider legacy railways, including Russia and Uzbekistan, have sought to develop a high-speed railway network in Russian gauge. There are no narrow gauge high-speed railways. Countries whose legacy network is entirely or mostly of a different gauge than 1,435 mm (56.5 in) – including Japan and Spain – have often opted to build their high speed lines to standard gauge instead of the legacy railway gauge.
High-speed rail is the fastest and most efficient ground-based method of commercial transport. Due to requirements for large track curves, gentle gradients and grade separated track the construction of high-speed rail is costlier than conventional rail and therefore does not always present an economical advantage over conventional rail.
Multiple definitions for high-speed rail are in use worldwide, with various international organisations and regional bodies establishing different standards. Several countries have also developed their own legal definitions and technical standards for high-speed rail.
International Union of Railways definition
The International Union of Railways (UIC) identifies three categories of high-speed rail:
Category I: New tracks specially constructed for high speeds, allowing a maximum running speed of at least 250 km/h (155 mph).
Category II: Existing tracks specially upgraded for high speeds, allowing a maximum running speed of at least 200 km/h (124 mph).
Category III: Existing tracks specially upgraded for high speeds, allowing a maximum running speed of at least 200 km/h, but with some sections having a lower allowable speed (for example due to topographic constraints, or passage through urban areas).
A third definition of high-speed and very high-speed rail requires simultaneous fulfilment of the following two conditions:
Maximum achievable running speed in excess of 200 km/h (124 mph), or 250 km/h (155 mph) for very high-speed,
Average running speed across the corridor in excess of 150 km/h (93 mph), or 200 km/h (124 mph) for very high-speed.
The International Union of Railways prefers to use "definitions" (plural) because they consider that there is no single standard definition of high-speed rail, nor even standard usage of the terms ("high speed", or "very high speed"). They make use of the European EC Directive 96/48, stating that high speed is a combination of all the elements which constitute the system: infrastructure, rolling stock and operating conditions. The International Union of Railways states that high-speed rail is a set of unique features, not merely a train travelling above a particular speed. Many conventionally hauled trains are able to reach 200 km/h (124 mph) in commercial service but are not considered to be high-speed trains. These include the French SNCF Intercités and German DB IC.
The criterion of 200 km/h (124 mph) is selected for several reasons; above this speed, the impacts of geometric defects are intensified, track adhesion is decreased, aerodynamic resistance is greatly increased, pressure fluctuations within tunnels cause passenger discomfort, and it becomes difficult for drivers to identify trackside signalling. Standard signaling equipment is often limited to speeds below 200 km/h (124 mph), with the traditional limits of 127 km/h (79 mph) in the US, 160 km/h (99 mph) in Germany and 125 mph (201 km/h) in Britain. Above those speeds positive train control or the European Train Control System becomes necessary or legally mandatory.
The European Union Directive 96/48/EC, Annex 1 (see also Trans-European high-speed rail network) defines high-speed rail in terms of:
Infrastructure: Track built specially for high-speed travel or specially upgraded for high-speed travel.