Objects inside a train (or other vehicle) feel centrifugal force as it speeds around a curve. Tilting trains are designed to compensate for the g-force by tilting the carriages towards the inside of the curve. This allows objects in the carriage to remain at their current position.
Trains tend to lean into curves because any object that is not fixed to its place will be forced over the edge of the moving carriage. If the train is going too fast for this not to happen, then it is dangerous and should be slowed down or stopped before turning into a curve. Objects such as luggage and passengers that might be thrown from their seats if the train is going too fast could be injured or even killed.
The amount that a train leans into a curve is called its "slope." A level track does not require a leaning train; instead it stays on an even plane as it enters the curve. A steeply graded track requires a deeply tilted train.
Trains can be either single or double ended. A single end train has one set of wheels at each end whereas a double-ended train has two sets of wheels at each end. When a train turns, it must turn at both ends simultaneously in order for it to remain balanced.
The train does, in fact, tilt when it turns around a curve, but the tilt degree is too slight for the passengers to notice. This tilt is caused by the rails being positioned around a curve. When a train curves, the outer wheel must go a greater distance than the inner wheel. Therefore, the train has to tilt away from the direction it is going to prevent the wheels from slipping.
When a train turns a corner, the driver will apply the locomotive's power to one side of the train first. If the track is straight, the whole train would now be turning simultaneously with no difference between front and back. But since the track is not straight, only some of the cars will be facing the same direction as the rest. The driver thus has to force some of the vehicles to turn more than others. This creates a small amount of imbalance which causes some of the cars to lean slightly toward the corner.
The amount that each car leans varies depending on how sharp the corner is. Cars at the outside of the curve tend to lean farther than those in the middle because they are turning faster and need more room. Trains with many flatcars or freight cars can also experience significant tilting at sharp corners because there is not enough space between them to allow for proper alignment.
This is because to the low center of gravity, and the additional tilting only impacts the carriage bodies rather than the bogies (the undercarriage). Tracks already have built-in corner tilts to counteract centrifugal force. Extra tilting is all about coffee. The more you tilt a train, the more it drinks.
Virgin Trains introduced this feature as part of its customer experience strategy, with the aim of reducing the amount of time that passengers spend waiting at stations. By allowing more rapid acceleration from a standing start, this should make journeys shorter while still giving passengers an enjoyable experience. It also allows for more efficient use of track facilities by not requiring parallel parking of carriages.
This concept was first demonstrated on the Venice Simplon-Orient-Express in 1983, and has since been adopted by many other rail companies around the world. It can be seen on some UK trains operated by Grand Central Railway and West Coast Railways.
The reason some people think there is something wrong with your mind if you like driving trains is because they don't operate any other way. If you want fast trains with no delay rewards, then this is the way to go. There are other operators who run more conventional trains with fixed routes and set schedules but this doesn't mean they're any less effective than Virgin or any other operator who chooses to tilt their trains.