Rail passengers face slower train journeys and a reduced timetable if summer heatwaves become more frequent with climate change.

The train derailment near Lewes in East Sussex on Thursday – the hottest day of the year – has sparked fears about the potential impact of higher temperatures on the rail network.

A second derailment happened less than 24 hours later in Essex on Friday, leading to further concern that parts of the rail infrastructure may be struggling to cope with intense weather.

The Labour Government may have to spend more upgrading infrastructure to help the network adapt to the changing climate, experts told The i Paper.

The cause of Thursday’s overturned Southern Rail commuter carriages – which left 20 people injured, including two serious injuries – is not yet known.

The cause of the partial derailment of a Greater Anglia train near Wickford in Essex is also unknown. The rear carriages were derailed in an upright position shortly after 2pm on Friday, but no injuries were initially reported.

But heat expansion causing rail lines to buckle is one possibility that will be looked at by investigators, said industry experts.

Footage from Lewes revealed a section of track that the overturned train had passed over was badly warped. However, the derailing itself could have caused the movement, said experts.

Painting rails white and ‘re-stressing’ track

Network Rail has explained that rails are “stressed” – carefully adjusting their length to reduce tension – to help them resist the effects of high temperatures.

“In Britain, our rails have a target stress-free temperature of 27 degrees,” Network Rail said in a post on X last month.

Re-stressing the network for the far-higher temperatures seen this summer has not been deemed necessary because the lines also have to deal with cold temperatures in the British winter.

However, Network Rail said it was taking steps to adjust to more severe summers: including painting rails white to reflect sunlight, fitting additional anchors to sleepers and re-stressing sections of rail lines.

The nation’s network operator also pointed out that train speed restrictions are needed in hot weather to reduce the impact on the lines. It can mean fewer trains to avoid lines become overcrowded.

Phil Blythe CBE, professor of intelligent transport systems at Newcastle University, said it could take “a decade or more” to adapt the UK’s rail infrastructure to extreme heat, he said.

Tough decisions will have to be made on priorities because “there isn’t much money around”, warned Prof Blyth – who leads the DARe hub of academics and transport industry leaders looking at climate resilience.

Passengers could face both “slower trains and reduced service” in the summers ahead “until a lot of these improvements can be made”, said Prof Blythe.

John Lawrence, chair of the Institution of Engineering and Technology (IET)’s railway technical network, also said higher temperatures could lead to reduced timetables.

“In hot weather we have to reduce the density of trains to enable trains to run more slowly.”

Dr Ioannis Koliousis, at expert in logistics at Cranfield School of Management, said trains could be slower and less frequent in the hotter summers expected with climate change.

“You could be looking at reduced capacity in services in the summer in the years ahead,” said Dr Koliousis – who also warned of more short-notice cancellations in heatwaves.

Why upgrades have to happen ‘quicker’

More investment was needed to upgrade track, signalling and monitoring, said Dr Koliousis.

“It could still take at least decade to make serious improvement,” said the logistics expert.

“Climate change means the Government will need to bring forward investment and make improvement happen a lot quicker,” he added.

Necessary upgrades were not happening “fast enough”, said Prof Blythe.

The rail industry “will have to make a case for more investment” in an effort to create a “more resilient network”, said Lawrence.

But he warned that upgrades could themselves hit rail services in the years ahead. “You have to consider cost and the amount of disruption it would require to continually re-stress lines and do lots of other work. It could be disruptive to passengers.”

Lawrence said there was already some investment going into buckle-detection technology – including video-based monitoring.

Derailment investigation under way

The Rail Accident Investigation Branch (RAIB) said on Friday it was conducting an “independent safety investigation” into the train derailment near Lewes.

Martin Frobisher, Network Rail’s group safety and engineering director, acknowledged that the public would be “concerned at the news of two derailments of passenger trains over a short period of time”.

“But I want to reassure them that Britain’s railways still rank among the safest in the world, and that safety is always our first consideration on the railway.”

He said RAIB had investigators on scene at the Wickford incident, as well as launching an investigation into the Lewes incident. Network Rail is also conducting its own internal investigations.

Frobisher asked that people “avoid speculating on the cause of any incidents” until more was known.

John Whitehurst, chief executive of Greater Thameslink Railway, which operates Southern, insisted that the network was safe. “The railway is safe,” he told BBC Radio 4’s programme. “These types of incidents are incredibly rare.”

The Department for Transport (DfT) is expected to set out the Government’s transport resilience strategy soon, which could set out priority upgrades for the rail network.

The DfT declined to comment.