Rising temperatures inevitably pose serious problems for Britain’s rail network.
Hot weather can cause overhead power lines to expand and sag, buckle the rails and even cause the ground beneath the railway to become unstable. This can lead to the closure of lines or force trains to operate at slower speeds, causing inevitable disruption for passengers.
Network Rail goes to huge lengths – and expense – to keep trains running during the sort of heat that parts of the country has faced in recent days. However, with stretches of the network laid down by the Victorians in the 19th century, it is clear that the challenge posed by the effects of climate change will only intensify in future.
Quite simply, it is now hotter than our rail infrastructure was ever designed for.
But what about a wholly new railway? As the first major new intercity line heading north from London in more than a century, HS2 is specified, designed and built with extreme weather – high summer heat and winter storms – at its heart.
Below, we set out how Britain’s new high-speed railway will reliably operate well into the twenty second century - whatever the weather.
Heat
Rails expand and can potentially buckle during periods of intensely hot weather. In the UK, rails on almost all the existing lines are attached to sleepers that sit on compacted but loose, rocky ballast. In the heat, they can move sideways if the expanded rails have no “expansion joints” to expand into. This can lead to speed restrictions and delayed trains, to services being suspended entirely in the worst cases.
HS2 by contrast will be built with solid concrete slab track. Its steel rails will be fixed ultra tightly to the slab track and thus unable to move. In addition, HS2 rails will be continuously-welded for mile upon mile, negating the need for the ends to have devices to accommodate rail expansion. However, Britain’s new high speed railway will have Rail Expansion Devices (RED) on major structures e.g. viaducts to mitigate longitudinal expansion in high temperatures. These devices prevent buckling by enabling rails to move freely as the structure expands.
Heatwaves can lead overhead powerlines to expand and sag. In such situations trains are slowed to prevent the cables being damaged, which can delay journeys for people and freight.
HS2’s overhead powerlines will be tensioned up to 10 kiloNewton metres tighter than on the conventional railway. Whatever the weather self-regulating counterweights positioned every 1200m along the line keep the wire at optimum tension, enabling a train’s pantograph (the arm that reaches up from the train to draw power) to maintain contact at speeds of over 200mph.
Wind
Overhead power lines can be brought down in strong wind, which causes major disruption to services. To mitigate this risk, HS2 will use an updated version of the overhead power lines developed for the for the Lyon – Marseille high speed line. This area of France can experience long periods of high winds known as the Mistral. To maintain reliability and keep TGV high speed trains running smoothly and to time the railway’s overhead power lines are designed to withstand prolonged periods of wind speeds up to 87.5 mph – Gale Force 12 on the Beaufort Scale.
To further enhance resilience masts carrying overhead electric wires are placed closer together on sections exposed to stronger winds e.g. on viaducts. Sharing the load of carrying the wires between more masts reduces the weight carried by each one, thus enhancing the line’s resilience against strong wind. Distances between masts on HS2 will range between 45 metres and 72 metres to ensure operational resilience.
Flooding
Most of the UK’s railways were laid down more than 150 years ago and in places it is overwhelmed at times of heavy rain. HS2 track is being built to withstand a one in 1,000-year flood event. It will be the only mainline in the UK to use solid concrete slab track – ensuring water is drained away swiftly, preventing erosion, instability and reducing the risk of disruptions. An extensive network of drains and culverts will form part of HS2’s infrastructure to carry rain water away from the line without increasing the risk of flooding elsewhere.
Landslips
Landslips can cause major disruption, with earth spilling onto the tracks from above or crumbling away beneath a line, causing the railway to be closed. This often happens on the existing railway after long periods of heavy rain, when the ground becomes saturated. HS2 is being built with significantly shallower cuttings and embankment slopes than seen on the existing Victorian-built railway to significantly improve stability. Furthermore, careful planting of vegetation, non-shrinkable soils (which avoid absorbing large quantities of water) and extensive in-built drainage will ensure stable ground around the railway.
Leaves
Thousands of tonnes of leaves fall onto railway lines in autumn each year from millions of lineside trees. They can be crushed by passing trains, creating a slippery layer on the rail similar to black ice on roads, making it harder for trains to accelerate or brake. HS2 will ensure that specific tree species will be avoided from day one to minimise the risks associated with leaf fall. Trees will also be planted well away from the line to avoid them being blown onto tracks during strong wind.
Cold
Points – moveable sections of the line that allow trains to switch between tracks – can freeze in cold weather, bringing the railway to a halt. All of HS2’s points will be fitted with a heating system that is automatically activated when temperatures drop below a certain level. This makes sure they will keep working, even in icy weather, helping to maintain the punctual operation of the railway.
Infrastructure condition monitoring
During construction of HS2, sensors will be built into the line’s physical infrastructure to continuously monitor its performance and condition. These will provide real-time analysis of assets including the track, bridges and overhead power lines – ensuring any potential failures can be repaired or replaced before they interrupt passengers services, helping to make HS2 one of the world’s most reliable railways.
