Why do trains get cancelled when there's a heatwave? Experts reveal why extreme heat makes Britain's public transport network grind to a halt

Daily Mail​

20-06-2025

As temperatures across the UK skyrocket, Britain's public transport network has ground to a halt.
Rail routes across England, Wales and Scotland are experiencing delays and cancellations, leaving thousands of passengers stranded.
Frustrated travellers have flocked to X to discuss the issues.
'That didn't take long… "Severe weather" has delayed nearly all departures from waterloo,' one user wrote, alongside a photo of the crowds.
British astronaut Tim Peake added: 'The mind boggles (as the train crawls its way to London) that we can build a space station that, for nearly 27 years, has coped with temperature fluctuations of +121C in the sun to -157C in the shade, 16 times a day, yet the signalling system on SW Trains flops at +30C.'
And one vented: 'Other countries have hotter weather and I'm sure their train service doesn't collapse like these lot.'
So, why do trains get cancelled when there's a heatwave?
Network Rail has revealed how abnormally high temperatures can cause steel rails across the network to buckle.
With temperatures in parts of the UK set to hit 32°C this weekend, we could see parts of the rails start to buckle
Britain's railway tracks cover more than 20,000 miles and are made from steel.
Most of the network can operate when track temperatures hit up to 46°C, according to Network Rail.
This is the equivalent to an air temperature of around 30°C.
However, with temperatures in parts of the UK set to hit 32°C this weekend, we could see parts of the rails start to buckle.
'When Britain enjoys a summer heatwave, rails in direct sunshine can be as much as 20°C hotter than air temperature,' Network Rail explained.
'Because rails are made from steel, they expand as they get hotter, and can start to curve. This is known as "buckling".'
Network Rail uses remote monitoring systems to keep an eye on its tracks.
When the systems detect that a section of track might be expanding too much and heading towards a buckle, Network Rail introduces local speed restrictions.
British astronaut Tim Peake added: 'The mind boggles (as the train crawls its way to London ) that we can build a space station that, for nearly 27 years, has coped with temperature fluctuations of +121C in the sun to -157C in the shade, 16 times a day, yet the signalling system on SW Trains flops at +30C'
Overhead wires can also overheat
Another issue for railway networks amid the heatwave is the risk of overhead wires overheating.
Overhead wires give power to trains by conducting electricity through the pantograph – an apparatus mounted on the roof of the train.
During heatwaves, the overhead wires can expand and sag, causing the train's pantograph to become entangled in the wires and requiring repairs.
'Slower trains cause lower forces on the track – this reduces the chance of buckling,' it explained.
Unfortunately, even with prevention measures in place, rails can buckle.
When this happens, the network is forced to close the line and carry out repairs before trains can run again.
'This can disrupt journeys because we often have to wait until the rail temperature has dropped before we can carry out these essential repairs,' it added.
Another issue for railway networks amid the heatwave is the risk of overhead wires overheating.
Overhead wires give power to trains by conducting electricity through the pantograph – an apparatus mounted on the roof of the train.
During heatwaves, the overhead wires can expand and sag, causing the train's pantograph to become entangled in the wires and requiring repairs.
Thankfully, much of the ageing overhead wires have been replaced with an auto-tensioned system, similar to those used European countries with more regular heatwaves, such as Italy.
'Modern overhead lines, such as those in place on the lines between Norwich, Ipswich, Colchester, Clacton, Harwich, Braintree, Cambridge and London Liverpool Street, and those installed on the Southend Victoria line, do not sag in high temperatures, avoiding the need for precautionary speed restrictions,' Greater Anglia explained.
One of the key ways that networks prevent tracks from overheating is by painting them white.
Dr John Easton, an executive panel member of the IET's Railway Technical Network, explained: 'This can reduce the track temperature by 5°C and reduces signalling failures which lead to significant disruption.
'This technique is also used in countries where high temperatures are more commonplace, such as Italy, where engineers often paint the inside faces of the rails white to reflect the sunlight and lower the risk of buckling.'
Most tracks across the UK are made of long pieces of rail that are stretched and welded together.
'There is much less chance of buckling in very high temperatures because there is reduced compression,' Network Rail added.
'When a track is made up from short rails bolted together, we leave small gaps between each one so that expansion doesn't cause a problem.'
Meanwhile, in some part of Britain's rail network, tracks are laid on reinforced concrete slabs, rather than on sleepers and ballast - a technique often used to prevent buckling in hotter countries.
While this also helps to prevent damage, it costs about four times as much to install as standard ballasted track.
Worryingly, climate change could increase the frequency and severity of extreme heatwaves, and cause even more chaos for railway networks.
'We work closely with many governmental and specialist organisations to prepare our railway for the climate changes projected over the next few years, decades and beyond,' Network Rail said.
WHY DO STORMS AND HOT WEATHER CAUSE DISRUPTION TO TRAINS AND PLANES?
HOW HOT WEATHER AFFECTS AIRCRAFT
Aircraft components begin to overheat and become damaged in extreme temperatures, with seals softening or melting.
If temperatures exceed 47°C (116°F), planes are grounded as some aircraft manufacturers can't guarantee the necessary engine propulsion.
HOW STORMS AND HOT WEATHER AFFECT FLYING
Aeroplanes fly because the speed of the aircraft causes ambient air to travel over the wings creating lift.
When the flow of air is disrupted, the wing loses, or gains, lift.
Hot air is less dense than cold air, which means aircraft require more engine power to generate the same thrust and lift as they would in cooler climes.
The warmer it gets, the less density there is in the air, which in turn results in less upwind for the wings.
Cumulonimus clouds, which occur during thunderstorms, can also be problematic as they are associated with heavy and sudden down pours of rain.
These clouds are often caused by periods of very hot weather.
Thunderstorms are a challenge for a pilot because there are several dangers like wind shear, turbulence, rain, icing and lightning.
HOW HEAT AFFECTS TRAINS
Thousands of miles of steel tracks cross the UK, much of which is exposed to sunlight.
Tracks in direct sunshine can be as much as 20°C (36°F) hotter than the ambient air temperature according to Network Rail, which manages Britain's railway infrastructure.
Heatwaves can cause points failures and signal disturbances, while in some places the tracks have buckled under the heat.
As temperature rises, the steel rail absorbs heat and expands, causing it to curve, or buckle.
The forces the temperature change provokes pushes and pulls the track out of shape.
Buckled tracks need to be repaired before trains can run again, leading to disruption.
Overhead lines can also expand and sag in extreme heat, bringing a risk of passing trains pulling them down.