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Why are trains cancelled when the weather gets too hot?

PUBLISHED: 12:28 19 June 2017

Some trains to and from London were cancelled due to the high temperatures on Wednesday.  
Picture: SARAH LUCY BROWN

Some trains to and from London were cancelled due to the high temperatures on Wednesday. Picture: SARAH LUCY BROWN

With almost 50 trains being cancelled in the region today because of the hot weather, Greater Anglia has provided details which help explain the disruption.

Why don’t rails get hot in Europe?

The truth is, they do. However, in countries which have been traditionally hotter than ours, rails are stressed to be able to withstand higher temperatures.

Rails in the UK are stressed to 27 degrees, the UK mean summer rail temperature. The rail can withstand some degree of change in temperature either side of this. However, when the air temperature is 30 degrees, the temperature on the rail can actually be up to 20 degrees higher, exceeding the maximum temperature our rails are designed to cope with.

The problem is that when steel rails get hot, they expand and this can cause a type of signalling problem called a track circuit failure and in extreme cases can cause a buckled rail.

If a rail buckles then the train service will not be able to run at all until the buckled rail is replaced with a new one.

When Network Rail assesses that the temperature of the rails is going to exceed what it is designed to cope with they put speed restrictions in place to help prevent buckled rails.

A train going over a hot rail at a slower speed exerts less pressure on the rail and will help to prevent it buckling. Because overhead power lines also expand in the heat and sag, it also prevents the train’s pantograph from pulling the sagging wires down.

It means have trains have to run more slowly, and there will be fewer trains as a result, but this is better than causing a bigger problem and then being unable to run any trains at all.

Why don’t we replace all our rails with ones stressed for higher temperatures?

The UK, and particularly East Anglia, is seeing hotter summers these days so this may seem like the obvious solution. The problem is that if UK rails were stressed to the same degree as those in very hot countries, there would be the risk of rails fracturing when the rails contract as the temperature drops in winter.

Please check before you travel

Greater Anglia would like to apologise for the inconvenience caused by heat-related speed restrictions. While they are in place, please check how trains are running before you travel.

Where possible, we will try to make you aware in advance of any predicted timetable changes due to hot weather.

There will be extra staff at stations giving out water to any customers caught up in any disruption and we will be doing everything we can to get passengers from a to b reliably and in comfort.

Network Rail’s planned programme of engineering works, including the renewal of overhead lines and new rails will help to make the railway more able to cope with hotter temperatures in the future.

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