傾斜式列車：ペンドリーノがカーブをより速く走る方法

The Curve Problem in Railway Physics

Every passenger on a conventional train knows the feeling of being pushed sideways into the window or towards the aisle as the train rounds a curve. This lateral force — centrifugal force, or more precisely, the centripetal acceleration that the train must impose on its passengers to follow the curved path — is not merely uncomfortable. It is the fundamental engineering constraint that limits how fast a train can safely travel on curved track.

Track cant (banking the outer rail higher than the inner rail) partially compensates for this force, but cant alone has limits: a train that is banked enough for a fast passenger express would be dangerously unstable for a slow freight train on the same track, and there are regulatory limits on how much cant a mixed-traffic line can use. The result, on conventional lines with their many curves, is that passenger trains must slow significantly below their maximum capability on curved sections.

Tilting trains exist to break this constraint. By tilting the passenger body of the train further into each curve, beyond what the track banking alone provides, they allow passengers to experience less lateral force at the same curve speed — or the same comfort at significantly higher curve speed. The technology has enabled significant journey time reductions on existing curvy routes without the cost of building new straight infrastructure.

Active Tilting: The Pendolino System

The most successful and widely deployed tilting train technology is the Fiat Ferroviaria system, marketed under the name Pendolino (Italian for "little pendulum"). Fiat Ferroviaria, later acquired by Alstom, developed the system through the 1970s and 1980s, bringing it to commercial service in Italy in 1988.

The Pendolino system is called active tilting because it uses powered actuators — hydraulic or electro-hydraulic cylinders — to tilt the passenger saloon relative to the bogie (the wheeled underframe). The tilt is controlled by sensors, typically accelerometers, that detect lateral acceleration as the train enters a curve. A computer receives this signal and commands the actuators to tilt the car body up to the system's maximum — typically 8 degrees — within about a second of curve entry.

Eight degrees of additional tilt sounds modest, but its effect is substantial. Combined with the track cant of perhaps 150 mm, the total effective tilt experienced by a passenger can reach levels equivalent to riding on a much more gently curved track. The practical result is that a Pendolino can typically travel through curves approximately 20 to 30% faster than a conventional train while keeping the lateral force on passengers within the same comfort range. On a route with many curves — such as the switchback mountain passes of Italy, the undulating English Midlands, or the heavily curved Finnish main lines — this translates directly into journey time savings of ten to twenty minutes per hour of travel.

One important refinement developed over time is the use of anticipatory rather than reactive tilt actuation. Early systems waited for the accelerometer to detect that the train was already in the curve before tilting, which meant a brief period of un-compensated lateral force and, more problematically, a moment of rapid tilt onset that some passengers found disorienting. Modern systems use track database information combined with GPS positioning to predict curve entry in advance and begin tilting before the forces appear, producing a smoother, more natural sensation.

Where Pendolinos Run

The Pendolino family has been adopted by railways across Europe and beyond, making it the most commercially successful tilting train system in history.

In Italy, the ETR 450, 460, and 600 series Pendolinos have operated on the classic network since 1988, allowing competitive journey times on the curvy lines between Rome, Florence, and Venice that predate the new high-speed lines.

In the United Kingdom, the Class 390 Tilting Train (marketed as Avanti West Coast's Pendolino) operates on the West Coast Main Line between London Euston, Birmingham, Manchester, and Glasgow. The line has significant curvature through the Lune Gorge and over Shap and Beattock summits, and the Class 390's tilting ability allows it to maintain higher speeds through these sections than a conventional train could safely achieve.

In Finland, the Sm6 (Pendolino) has operated on Helsinki to Tampere, Turku, and Oulu routes since 1995. Finland's railways have extensive curves, and the tilting ability yields useful journey time savings on these long-distance domestic routes.

Other Pendolino operations include Portugal (Alfa Pendular), the Czech Republic (SC Pendolino), and Russia (former Sapsan-adjacent ET 400 trials). Spain's Alvia trains use a similar active tilting system on routes where the line converts between standard and Iberian gauge.

Passive Tilting: The Talgo Approach

An alternative to active tilting is passive or natural pendular tilting, the approach taken by the Spanish manufacturer Talgo. In Talgo's system, the passenger modules are not mechanically forced to tilt by actuators. Instead, the centre of gravity of each car body is raised above its pivot point, so the car naturally swings outward under centrifugal force — like a pendulum — and the geometry of the pivot produces an inward tilt relative to the car's floor.

Passive tilting is mechanically simpler and requires no actuators, sensors, or complex control software. Its disadvantage is that the maximum tilt angle achievable is lower than active systems — typically around 3.5 degrees compared to 8 degrees for Pendolino — which means smaller speed benefits on curves. It is also a reactive system: the tilt happens in response to actual forces, which means there is always a brief instant of un-compensated force at curve entry.

Talgo's system is also notable for a different reason: it uses individual axles with independently rotating wheels rather than conventional bogies, allowing Talgo cars to articulate over curves very efficiently. This design contributes to a notably smooth ride and enables the variable-gauge wheelset technology discussed in our rail gauge guide.

Motion Sickness: The Tilt Problem

Tilting trains are not without their discomforts. The mismatch between what the body feels (reduced lateral acceleration due to tilt) and what the eyes see (the visual scene apparently tilting as the car body tilts) can trigger motion sickness in susceptible passengers. This is the same mechanism that causes seasickness or car sickness — a conflict between the vestibular system's perception of motion and the visual cortex's perception of the environment.

Not all passengers are affected, and most adapt over the course of a journey, but train operators have had to be thoughtful about tilt angles and tilt rates to minimise complaints. Some Pendolino services operate with reduced tilt angles compared to the system's maximum capability, accepting a smaller speed benefit in exchange for better passenger comfort. The anticipatory tilt systems in modern trains help significantly by reducing the sudden onset of tilt that early systems produced.

Why Tilting Trains Are Not Used on High-Speed Lines

Given the speed benefits of tilting, one might wonder why Japan's Shinkansen or France's TGV lines do not use the technology. The answer is that dedicated high-speed lines are designed with curves so gentle that tilting provides no useful benefit. A curve with a radius of 7,000 metres allows a non-tilting train to traverse it at 350 km/h within normal comfort limits. There is simply no physics problem for the tilt mechanism to solve.

Tilting technology is most valuable precisely where high-speed new construction is not economically justified — on existing curvy routes where modest speed improvements can be achieved without the enormous investment of a new line. This makes tilting trains and high-speed new construction complementary rather than competing strategies, and many countries have deployed both: new HSR corridors where demand justifies the investment, and tilting trains on secondary routes where it does not.

To learn more about the vehicles that popularised tilting technology, see our Pendolino glossary entry.