What gradient can trains climb?

Train Gradient Limitations

In standard operation, trains are typically limited to a gradient of 10%, meaning they can ascend or descend an incline that rises or falls 10 meters (32.8 feet) for every 100 meters (328 feet) of horizontal distance. This limitation is imposed due to several factors that affect train performance and safety.

• Tractive Effort: The tractive effort of a locomotive is the force it can exert to pull or push a train. As the gradient increases, the tractive effort required to ascend the incline also increases. Beyond a certain point, the locomotive may not have sufficient tractive effort to overcome the gravitational force pulling the train down.

• Adhesion: Adhesion is the friction between the train wheels and the rails, which allows the wheels to grip and propel the train forward. As the gradient steepens, the weight of the train increases the force acting on the wheels, reducing their adhesion. This can lead to wheel slip and loss of traction.

• Stability: As a train climbs an incline, its center of gravity shifts towards the downhill side. This can create instability, especially for long and heavy trains. The steeper the gradient, the greater the instability becomes.

Rack Railways

To overcome these limitations for steeper inclines, specialized rack railways are employed. Rack railways utilize cog wheels on the locomotive or railcar that interlock with a toothed track. This system provides additional traction, allowing trains to climb gradients of up to 25% or more.

Rack railways are commonly found in mountainous regions or areas with steep terrain, such as the Swiss Alps and the Rocky Mountains. They are particularly suitable for short-distance passenger trains and tourist railways, as they offer a reliable and efficient way to traverse steep slopes.

Conclusion

Trains are limited to a 10% gradient for standard operation due to constraints on tractive effort, adhesion, and stability. For steeper inclines, rack railways are utilized, which employ cog wheels and a toothed track for increased traction. Rack railways play a vital role in connecting remote communities and providing access to scenic locations in mountainous regions worldwide.