A tilting train is a train with a tilting mechanism that enables increased speed on regular railroad tracks.
Introduction
Curved railroad tracks are usually tilted. The tilt angle is based on a particular speed and has the effect that at this speed the passengers do not experience the centrifugal force. This makes the ride more comfortable. The disadvantage is that if a train halts in a curve, the tilting is not comfortable.
If a train moves faster than corresponds with the tilt angle of the track than the passengers do experience (part of) the centrifugal force, which is not comfortable. This restricts the allowable speed more than the (essential) requirement that the centrifugal force does not push the train off the track, that would happen only if the speed would be much higher.
Tilting trains
Tilting trains are trains of which the upper part, in which the passengers are seated, can be tilted sideways. In a curve to the left, it tilts to the left to compensate the centrifugal push to the right, and conversely.
The train may be constructed such that inertial forces cause the tilting, or it may be controlled by a computer.
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. 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.
One of the first trains with tilting technology was the former class 403 by Deutsche Bundesbahn, now Deutsche Bahn AG that was used for airport transfer from Düsseldorf to Frankfurt some decades ago (see also: AiRail Service). Tilting technology tried to improve the speed on the excessively curved Rhine Valley route. Shortly after the train went into service, tilting technology had been disabled as many passengers got sick due to sudden and heavy tilting.
Trains with tilting by inertial forces: