Rail passengers are facing days of disruption as temperatures soar to almost 40C in the UK this week.
Several operators, including Great Western Railway, Avanti and LNER, have urged for services to be used for “essential travel only” on Wednesday and Thursday as a “heat-dome” settles over western Europe.
Train performance website trains.im shows 11 per cent of services across Britain were either cancelled or delayed by more than half an hour as of Wednesday morning.
With a rare red weather warning forecast for parts of England and Wales until at least Friday, here’s why extreme heat can cause serious problems for trains and rail infrastructure.
Read more: UK heatwave live
Why are trains cancelled during a heatwave?
According to Network Rail, hot weather can be “as challenging as freezing winters”.
The rail operator said that hot weather can affect the rails, overhead power lines and the ground on which the track sits.
Around 44 per cent of all passenger trains in the UK are powered by overhead lines, according to the Office for Rail and Road (a further 26 per cent of trains – mostly in the South East – get power from a live “third rail”). As mapped by data website Rail Maps, routes electrified by overhead power lines include the East and West Coast Main Lines and routes from London to Cardiff.
In hot weather, the overhead lines can expand and sag, which means temporary speed restrictions have to be imposed to reduce forces on the track.
This in turn minimizes the risk of “buckling”, when structural distortion where steel tracks warp or bend due to extreme heat.
Thousands of miles of steel track make up the UK’s rail network, absorbing heat up to 20C hotter than the air temperature, said Network Rail.
It added that most of the network can operate when track temperatures reach up to 46C (roughly 30C air temperature) and rails have been recorded at temperatures as high as 51C.
As steel expands when it gets hot, rails lengthen, causing tension against their neighbouring pieces of track.
When this happens, trains are stopped for safety, as “if there is no room for the rail to expand, the rail can buckle and we need to close the line to fix it before trains can run again,” says Network Rail.
John Lawrence, chair of the Institution of Engineering and Technology Railway Technical Network, said: “Ambient temperature and solar gain combine to push temperatures very high at track level and in trackside equipment. Track buckles and dewirements are what really worry engineers – despite years of focus, investment and improvement, rails can still buckle in extreme heat.
“That brings derailment risks, and overhead lines can sag and catch on pantographs, halting train movements or forcing lengthy reroutes.”
He added that “hidden failures” resulting from heat stress include signalling control, power supplies, and trackside telecoms.
“Lineside fires, sparked by anything from discarded rubbish to passing trains, can cause further disruption,” said Lawrence.
According to Lawrence, rail operators can tackle overheating tracks by painting them white – something which can lower track temperatures by 5C – and lubricating rail joints to allow for expansion.
Several operators already use temperature sensors on the rails and thermal imaging drones and helicopters to spot overheating equipment and carry out repairs overnight.
Read more: UK heatwave live: Met Office issues new extreme heat and thunderstorm weather warnings
Read MoreEuropean holiday hotspots with extreme heat warnings this week
London’s Tower Bridge among major UK attractions closed during extreme heatwave
London Euston trains cut amid railway track ‘buckling’ fears during UK heatwave
Tour de France inspired cycling holidays for your next global adventure
GWR, LNER, Chiltern and Avanti train passengers urged to stay home
UK drivers risk £110 fines for keeping cool in cars during heatwave
