Why does the ‘wrong type of snow’ affect the railways?

Published 28th January 2013

London - Powder or Flakes? Ice or Floods? What is worse for our railways?

The recent spell of icy weather has caused some disruption to rail services - especially in areas equipped with electric services powered by what is known as a third rail. This is an electrified rail carrying a notional 750 volts DC allowing trainbourne pickup‘ shoes’ to collect power for the train.

Sub-zero temperatures and snow provide different challenges for routes that are equipped with overhead lines electrified at 25,000 volts AC current.

Wrong type of snow

When the snow is of the ‘powder’ variety, it blows around after being disturbed by trains moving at anything above 25mph. Many will have seen the mini-blizzard created by fast trains travelling at up to 125mph going non-stop through stations in recent days.

In the cold winter a couple of years ago, Eurostar suffered badly from the effects of this powder snow when the trains ran into the Channel Tunnel. The minute granules of powder snow are drawn inside the power car motors and onto the electrical equipment. While the cold air is continually circulating, the snow is harmless. Inside the Channel Tunnel, the ambient temperature is high due to a combination of its length and the trains operating through it generating heat.

This, combined with the duration of the sub-surface journey enables the snow to melt inside the power cars which meant that water got into the electrical equipment and it all then went wrong for obvious reasons! This has now been cured by modifications.

Snow joke!

To a lesser degree, this also happens to domestic electric trains also causing disruption. What is more common is that the snow gets caught in the door opening and coupling mechanisms. This forms a barrier to the electronic sensors that provide the interlocking safety systems to engage meaning that the system thinks the train is unsafe to move – so it won’t!

This is why some trains carry bin-liner type coverings over their couplings to prevent snow sticking to them. So far as door mechanisms are concerned, temporary greenhouse type buildings are built and are heated to make the powder snow accumulations on the train to melt before it goes into service.

Snow points

The track is obviously prone to disruption from snow. If the snow is heavy and with large flakes, it can stick in between point switch blades. When the points change, snow can become compressed meaning that the points to not work properly and can cause a derailment or an interlocking signal track circuit failure. To combat this, Network Rail has installed points heaters at key junctions which melts the snow avoiding the problems.

Arcing Overheads and 3rd rails

The overhead wires suffer from icing and electric trains use pantographs to collect the power. Where ice forms on the wire, this causes interruption to the power collection and creates dramatic arcing flashes.

Where a third rail is provided, the same principle applies. Although de-icing trains are provided and run as required, the fluid can melt the ice, or prevent it from forming. But, if it rains, the fluid is washed off the third rail and the ice often reforms. This can be seen from the arcing flashes from alongside a train which also jolts as its power supply is interrupted.

Carriage washing difficulties

Trains are put through a washer most nights to keep them clean. These washing plants are located outside and in freezing temperatures, cannot be used. Not only because of ice, but even if the train is washed, ice can form afterwards and render doors and couplings useless.

Tunnels provide more problems as they are normally damp, if not wet places by their very nature. So when extremely low temperatures occur, huge icicles form inside them and have caused some derailments and broken windows as ice falls from the roof onto and around trains.

Wind and flooding

High winds and flooding also affect the railways. Even simple things such as how a field adjacent to a railway line is ploughed can affect the railway. The West Coast Main Line has been flooded in the past because some fields were ploughed in such a way that the water ran onto the railway line. Had the furrows been ploughed the other way parallel to the railway, (90 degrees different) the rainwater would not have flowed onto the line. Run-off from the M5 near Bromsgrove has also caused railway flooding in the past.

High winds bring their own problems such as debris from gardens blowing onto the track. It is not unknown for ripped off roofs, garden sheds and children’s trampolines to land on the lines or overhead wires!

In the past….

Before today’s mechanical snow and ice clearance methods were introduced, various methods of snow protection were used. These ranged from snow fences on exposed routes and the remnants of these can still be seen on the Settle & Carlisle line near Dent. Until maybe 20 years ago, permanent way teams dug out the track from underneath the snow in exceptionally heavy snow when ploughs could not be used.

There a few avalanche shelters used in Scotland today but prevention and preparedness is the strategy today rather than clearance. Snowploughs are still used usually fixed to diesel locomotives but sometimes, heavy duty ones are used, propelled by a locomotive.

‘The trains run OK in Russia’

When so called pundits say that trains run in Russia or Switzerland like clockwork every winter, they are not looking at reality. The UK climate is not the same as say at an altitude of 2500metres in the Alps or a Continental Climate such as in Russia. Where snow and ice is a reality for a given period every winter, appropriate investment will be made to counter the climate. Spells of poor weather are not the same as a type of climate.

If the UK’s railways were to invest for every type of extreme weather we experience, then fares would rise and the economy would be worse off. The rail industry is actively planning on how to combat climate change, but that is an emerging story.

So don’t always blame the railways, compared to airports and roads, they are a good option 99% of the time.

 
 

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