Tilting train
A tilting train is a train that has a mechanism enabling increased speed on regular rail tracks. As a train rounds a curve at speed, it experiences centripetal force, pushing on objects inside it. This can cause packages to slide about or seated passengers to feel squashed by the outboard armrest, and standing passengers to lose their balance. The train can physically tilt on one side, eventually causing it to derail. Tilting trains are designed to counteract this by tilting the carriages towards the inside of the curve. The train may be constructed such that inertial forces cause the tilting, or it may have a computer-controlled powered mechanism.
The first passive tilting car design was built in the United States 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 tilting train to enter commercial service in 1968 in the US and Canada. Japan similarly experimented, from the late 1960s, through the 591 Series that developed into the highly successful Hitachi 381 series, that has been in service since 1973.
In parallel, Fiat Ferroviaria produced the experimental Y 0160 in 1970, that would evolve into the Pendolino family, in 1976, and operated in 11 countries. 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 also began experiments with its Advanced Passenger Train which pioneered the active-tilt concept, along with in-cab signaling, to permit High Speed Rail services on conventional tracks. The APT family used hydraulic rams on the bottoms of the carriages to tilt them, rotating them around their center point rather than swinging outward. This had the advantage of keeping the carriage centered over the bogies, which reduced load on the rails, and could be turned off when navigating switches. Due to lengthy political delays, the APT did not begin service testing until 1979, entering limited scheduled service in December 1981, the media describing the initial revenue run as both fifteen years late, and the queasy rider; the sets only briefly entering full revenue operation in 1985, before being withdrawn and the associated technologies sold to Alstom / Fiat Ferroviaria. 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.
Design
Aeroplanes and bicycles tilt inwards when cornering, but automobiles and trains cannot do this on their own. Vehicles with high centers 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 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 is determined by the intended vehicle speed—higher speeds require more banking. However, 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".
More limited and slower tilt could be achieved using active, or 'forced', tilting mechanisms. In trains adopting these mechanisms, tilt is initiated by computers, which 'force' train bodies to tilt at specific angles based on track information. This information could be stored on board or detected using a sensor at the front of the train or using automatic train stop beacons. The slight delay in reacting to this information leads to a short period of sideways force while the cars react. It was found that when the cars tilt just at the beginning of the curves instead of while they are making the turns, there was no motion sickness. Researchers have found that if the tilting motion is reduced to compensate for 80% or less of lateral apparent force, then passengers feel more secure. Also, motion sickness on tilting trains can be essentially eliminated by adjusting the timing of when the cars tilt as they enter and leave the curves.
A similar technology widely adopted across Asia and Oceania, known as controlled passive tilt, achieves a similar effect by using on-board computers to limit tilt, initiated using inertia. Automatic train stop beacons are used to inform computers of the precise location of these trains and limit natural tilt to angles specified by track data.
High-speed trains
A high-speed tilting train is a tilting train that operates at high speed, typically defined as by the European Union to include for upgraded track and or faster for new track.Tilting trains operating at or more on upgraded track include the Acela and the Avelia Liberty in the US, the X 2000 in Sweden, the Pendolinos and Super Voyagers in the United Kingdom, the ICN in Switzerland and the ICE T and ICE TD in Germany.
Some older high-speed lines were built for lower line speeds ; newer tilting trainsets can maintain higher speeds on them. For example, the Japanese N700 Series Shinkansen may tilt up to one degree on the Tōkaidō Shinkansen, allowing the trains to maintain even on radius curves that previously had a maximum speed of.
Many high-speed trainsets are designed to operate on purpose-built high-speed lines and then continue their journeys on legacy lines, upgraded or not. Where the legacy lines justify it, a tilting train may operate at higher speeds on the latter, even if below the normal threshold, whilst operating at or faster, usually with tilt disabled, on the high speed lines.
History
Pendulum car
The first experimental tilting train concept was the pendulum-suspension "chair" cars designed by the Pacific Railway Equipment Company. The first prototype, with an articulated bogie system, was built in 1937 and tested on the Atchison, Topeka and Santa Fe Railway that year. The company built another three pre-production models in 1939, using more conventional fore-and-aft bogies, and these saw some use with the San Diegan, among others. Mounted on high springs, the car tilted inwards on curves to counterbalance the cant deficiency with the induced centrifugal force. The opening of World War II prevented any immediate orders, and the concept was not revived in the post-war era.SNCF experiment
In 1956, SNCF experimented with a self-propelled pendulum car, which also relied on centrifugal force. This experiment demonstrated the need for an active suspension system to tilt the coach bodies.Talgo Pendular
The Spanish Talgo company had introduced the first widely successful shared-bogie system, which allowed cars to be connected end-to-end using a single bogie instead of each car having its own bogies at either end. This design saves weight and can reduce rail wear.In the early 1950s, the Spanish National Railway, Renfe, experimented with passenger cars that combined the Talgo bogie with a new passive tilting system. This system used a large A-frame connected to the centre of the bogie that was as high as the cars. At the top of the A was a bearing system that the cars attached to, and a spring and damping system to smooth its motion. Because the cars were connected at this high point, they could swing to either side around the bearing axis, and this caused them to naturally pendulum outward on curves.
The first test of a Talgo in the United States was the John Quincy Adams with Fairbanks-Morse P-12-42 tested by the New York, New Haven & Hartford Railroad in 1957–1958. Due to technical troubles and the precarious financial state of the New Haven railroad, the trainset was stored. The idea caught the interest of the Chesapeake & Ohio Railway, who began development of what would become the UAC TurboTrain using the same system. The TurboTrain entered service in the US and Canada in 1968.
The first successful European tilting train design was the Talgo in Spain, developed in the 1970s as a lightweight, fast train using passive tilt. Renfe, adopted the system widely, but was restricted to the Iberian peninsula initially.
The first full commercial application of passive tilting trains appeared in early 1980s with the Talgo Pendular. Talgo is currently in its 21st generation of production. Talgo trains are in service in various parts of Europe, and built under licence in Latin America and Asia. In North America, Amtrak uses Talgo trains in its Cascades service in the Northwest.
The first Talgo tilting series were the "pendular" ones from 400 series onwards.