Tarmac softens in the summer heat, which may cause problems on the roads, but even trains running on steel rails are not immune.

Railways in the UK are generally designed to operate within a 45C temperature range. The rails expand slightly in the heat, and excessive temperatures can produce “sun kink” with rails warping into S-shapes. The effect is small but the distortion can derail fast trains, so speeds are reduced for safety.

Thermal expansion also causes overhead power lines to droop, and in extreme conditions they may contact trees or other obstacles. This can be solved with auto-tensioning, balancing weights or springs that adjust to changing conditions, but not all power lines have been updated.

Signalling equipment housed in railside metal cabinets is also vulnerable. The inside of these cabinets can reach 70C during a heatwave, causing electronics to fail. Southeastern has been testing IsoMat, a flat aluminium unit that attaches to a signal box and provides cooling. IsoMat is a passive heat exchanger containing sealed internal channels filled with liquid that evaporates and condenses, drawing heat away from the sensitive electronics.

None of these problems are entirely new but they are now more common. Hopefully, hotter summers should drive investment in mitigation measures so that delays due to excessive heat become less rather than more frequent.