A tilting train is a train with a tilting mechanism that enables increased speed on regular railroad tracks.
Introduction
As any vehicle rounds a curve at speed, independent objects inside it experience so-called centrifugal force since their inherent momentum forward no longer lies along the line of the vehicle's course. This can cause packages to slide about on the floor, people seated in chairs to feel squashed against their outboard armrest, and standing passengers to lose their balance.
Aeroplanes and bicycles simply tilt in place; but automobiles and railway trains cannot do this on their own. To make their turns easier, the roadway of a high-speed highway or railway is canted inward around the curve. To a passenger in such a vehicle, the outward centrifugal force is countered by an inward gravitational one, thus removing the discomfort. (It should be noted that vehicles with high centers of gravity rounding very sharp curves at very high speeds may in fact topple over altogether; banking would also be the answer to counteract this threat. However, since passenger comfort becomes an issue at much lower speeds and gentler curves, railway designers, having kept their passengers comfortable, do not need to worry about trains overturning.)
The particular angle of tilt ("superelevation") is determined by the speed at which it is intended that vehicles will pass — faster 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 the new high-speed trains would be unacceptably over-tilted for slower-speed local passenger or freight trains which must share the lines. France, building its TGV, avoided the problem by building a special new rail network for the high-speed trains which minimized curves, likewise Japan's bullet train and many other high speed lines have necessited new infrastructure.
Other countries, with less elbow room, weaker governmental planning powers, and more hilly terrain, were unable to follow. Specifically, the UK state railways invested heavily in tilting train technology to overcome the limitations of a rail network contructed through heavily built up areas very early on in railway history when running speeds were very slow. Italian State railways has been another heavy investor in tilting technology for their mountain ridden country.
Tilting trains
Tilting trains are trains the upper part of which, where the passengers are seated, can be tilted sideways. In a curve to the left, it tilts to the left to compensate for the centrifugal push to the right, and conversely.
The train may be constructed such that inertial forces themselves cause the tilting, or it may be actively induced by a computer-controlled mechanism.
The first tilting train to enter into regular service was the United Aircraft Turbo train, on Canadian National Railways, in 1969. Plagued with frequent breakdowns, it nevertheless assured daily service between Montréal and Toronto until it was retired in 1984, having been replaced by Bombardier LRC trains. The UAC Turbo was inspired by the Talgo, and had a passive (non-power assisted) tilting mechanism; its ride quality was rather mediocre).
Another tilting train to enter into regular service was the Pendolino. The original ETR 401 train was built by FIAT in 1975 for the Italian State Railways following a prototype in 1970 and ran successfully for many years. The Pendolino project ticked over on a low budget developing a hypothetical successor until the early 80s when the go ahead was given to build a new fleet, which was the ETR450. Later developments of this train have been very successful and are used throughout Europe.
In the 1970s and 80s, following the success of its InterCity 125, British Rail built a tilting train called the Advanced Passenger Train. British Rail was never able to make the train reliable enough to go into service and so the project was scrapped, although the project was purchased by the Pendolino group to enlarge their technology portfolio.
During tests passengers reported that the tilting motion made them nauseous. Subsequently it was learned that this could be prevented by reducing the tilt slightly, so that there was still some sensation of cornering.
Canada's contribution is the LRC (Light, Rapid, Comfortable) train, built by Bombardier. This train is rather conventional, having separable cars instead of being articulated, and whose cars can be intermingled with conventional non-tilt cars. It first entered service in the United States for Amtrak in 1980, only to be retired several years later. In Canada, it entered service in 1981, and is still in service. The LRC tilt-mechanism is power-assisted, driven by accelerometers. The ride quality is very smooth, even on the less-than-perfect Canadian rails.
Another early train with tilting technology was Deutsche Bahn's class 403, used for airport transfers between Düsseldorf and Frankfurt which entered into service in 1978 (see also: AiRail Service). An attempt was made to use tilting technology to improve speeds on the extremely twisting Rhine Valley route. Shortly after the train went into service, the tilting technology was disabled as many passengers experienced motion sickness due to sudden and heavy tilting.
Switzerland got its first tilting train ever in its territory (discounting the Cisalpino, which entered Switzerland in 1996) on May 28, 2000. The ICN (InterCity Neigezug, or InterCity Tilting Train) entered service, running first from Geneva via Biel/Bienne and Zürich to St. Gallen. It was a major carrier in the national exhibition Expo.02.
Many of the problems with motion sickness are related to the fact that a traditional servo system cannot respond instaneously to the change in trajectory forces, and even slight discrepancies whilst not being noticeably perceivable cause nausea due to their unnatural nature. The original ETR 401 used individual gyroscopes in each carriage so there was inevitably a lag, even though nausea had not been a major problem with this train. The APT was supposed to supercede this problem by using gyroscopes at the ends of the train and a master slave control system which defined a "tilting curve" for the whole train. It would appear that the technology of the era was not able to implement this technique as well as required.
Modern tilting trains have the blessing of the latest signal processing technology which reads the line ahead and is able to anticipate a very precise control signal to the individual carriages and complaints about nausea have become a thing of the past.
Some tilting trains run on narrow-gauge lines. In Japan there are many narrow-gauge lines in mountainous regions, and tilting trains have been designed to run on these. In Australia the link between Brisbane and Rockhampton, which uses tilting trains, now claims to be the fastest narrow-gauge link in the world.
Trains with tilting by inertial forces:
Trains with tilting controlled by accelerometers:
Trains with tilting controlled by a computer:
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