A tilting train is a train that has a mechanism enabling increased speed on regular rail tracks. As a train (or other vehicle) rounds a curve at speed, objects inside the train experience centrifugal force. This can cause packages to slide about or seated passengers to feel squashed by the outboard armrest, and standing passengers to lose their balance. Tilting trains are designed to counteract this by tilting the carriages towards the inside of the curve, thus compensating for the g-force. The train may be constructed such that inertial forces cause the tilting (passive tilt), or it may have a computer-controlled powered mechanism (active tilt).
The first passive tilting car design was built in the US in 1937, and an improved version was built in 1939. The beginning of World War II ended development. Talgo introduced a version based on their articulated bogie design in 1950s, and this concept was used on a number of commercial services. Among these was the UAC TurboTrain, which was the first (albeit short-lived) tilting train to enter commercial service in 1968 in the US and Canada. Parallel experiments in Japan and Italy through the 591 Series and the Fiat Y 0160 developed into the highly successful 381 series which began services in 1973 and is in service today, and the Pendolino family currently being used in 11 countries since 1976. All of these had problems with short curves like those in switchyards, where they tended to sway about. Also, because of the way the carriages always swung outward, they placed more weight on the outside of the curve, which limited their improvement in cornering speed to about 20%.
Starting in the late 1960s, British Rail began experiments with its Advanced Passenger Train (APT) which pioneered the active-tilt concept. This used hydraulic rams on the bottoms of the carriages to tilt them, rotating them around their centre point rather than swinging outward. This had the advantage of keeping the carriage centred over the bogies, which reduced load on the rails, and could be turned off when navigating switches. Due to lengthy delays, the APT did not begin test runs until 1981 and entered commercial service only briefly in 1985. By this time, the Canadian LRC design had become the first active tilting train to enter full commercial service, starting with Via Rail in 1981.
Fiat developed their Pendolino design into the most successful type of tilting train, with over 500 trains active in Europe. The concept of active tilt as a whole has been independently developed by many companies. Active tilting systems are widely used today.
Design
Aeroplanes and bicycles tilt inwards when cornering, but automobiles and trains cannot do this on their own. Vehicles with high centres of gravity rounding sharp curves at high speeds may topple over. To make their turns easier, the outer edge of a roadway of a high-speed highway or outer rail of a railway may be canted (raised) upward around the curve. The combination of tilt and centrifugal force combines to produce an effective acceleration that is down through the floor, reducing or eliminating any sideways component.
The particular angle of tilt ("superelevation") is determined by the intended vehicle speed — higher speeds require more banking. But with a growing desire in the 1960s and 1970s to build high-speed rail networks, a problem arose: the amount of tilt appropriate for high-speed trains would be over-tilted for lower-speed local passenger and freight trains sharing the lines. Japan's early bullet train efforts of the 1960s avoided this problem by laying all-new lines as part of a re-gauging effort, and France's TGV followed the same pattern. Other operators did not have this luxury and were generally limited to much lower speeds.
Spain's national railway Renfe took a domestic invention, the Talgo, and developed it into a reliable high-speed train for a low-traffic-density railway. British Rail invested heavily in tilting-train technology to overcome the limitations of a rail network located in space-constrained built-up areas. Italy's Trenitalia and the Japan National Railways have used tilting technology to speed express trains on conventional tracks through mountainous terrain.
Tilting trains are meant to help reduce the effects of centrifugal force on the human body, but they can still cause nausea, a problem that was widely seen on early "passive" tilting trains that exactly balanced the outward force. The effect could be felt under maximum speed and tilt, when the combination of tilting outside view and lack of corresponding sideways force can be disconcerting to passengers, like that of a "thrill ride".