Series: How does a train brake?
Part 1: Understanding the role of friction
In the world of trains, speed is often the star of the show. The rush of the landscape whizzing by is the sensation that captures our imagination. Yet, as any experienced engineer will tell you, the real hero of the railway isn’t the power to go, but the power to stop.
The ability to stop before reaching a danger point is vital to the safety of the railway system.
Trains do not rely only on a single technology for braking, but use several technologies, each with its own advantages and disadvantages.
This series of articles explains the basic technology used to brake trains.
In the first part, we look at a basic distinction between braking systems:
- Based on friction between wheel and rail
- Independent of friction between wheel and rail
Why is this distinction important?
Trains with steel wheels run on rails, that are also made of steel. The friction between wheel and rail is very low compared to the friction between rubber tire and an asphalt road.
In certain weather conditions the friction is even worse. Think of a rainy day in autumn when there are wet and slippery leaves on the track.
The braking force that can be applied using a braking system that relies on the wheel-rail friction is therefore limited and may not be sufficient to stop a train travelling at high speed before it reaches a danger point, especially on days when the weather is bad.
Modern trains are therefore usually equipped with systems based on the wheel-rail friction and one system not based on this principle.
Which technologies are used in which category? We will look at this question in the next article in the series.