Tilting Train - Rationale

Rationale

Airplanes and bicycles tilt in 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 — 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 high-speed trains would be over-tilted for slower-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 Railways invested heavily in tilting train technology to overcome the limitations of a rail network in built-up areas. Italy's Trenitalia has used tilting technology to speed trains 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 "active" 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". Researchers have found that if the tilting motion is reduced to compensate for 80% or less of lateral apparent force 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. Systems typically tilt the cars based on a sensor at the front of the train, and 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. To provide information about the upcoming curves before the front of the train reaches them, a GPS system is used.