Quote:

"Continuous Welded Rail (CWR) eliminates the expansion gaps of traditional jointed track by welding individual rail lengths into seamless strings of 300–500 metres or longer — constraining thermal movement internally through compressive and tensile stress in the steel rather than allowing physical expansion.

CWR is installed at a precisely specified “stress-free temperature” (neutral temperature), typically 25–30°C in temperate climates. Above this temperature the rail develops compressive stress; below it, tensile stress. Excessive compressive stress causes buckling (sun kink); excessive tensile stress causes pull-apart (cold fracture).

A 100-metre rail length changes in dimension by approximately 1.1 mm per °C of temperature change. A temperature swing of 50°C would create 55 mm of potential movement in a 100 m rail — which in jointed track would be accommodated by gaps, and in CWR must be constrained by the fastening system and ballast resistance.

The principal maintenance advantage of CWR over jointed track is the elimination of fishplate joints — the weakest link in the track structure, responsible for the majority of track defects including end-batter, bolt-hole cracks, and rail end corrugation.

Speed limits must be reduced on sections of CWR where buckle risk is elevated — typically when rail temperature exceeds the installation temperature by a defined margin (often 30°C above neutral temperature), or when track geometry has deteriorated and ballast resistance is insufficient to resist buckling forces."

On the date of the Lewes rail derailment, the temperature was around 27c, so should have been well within the operational parameters of CWR. Buckling rails are only one possible cause of the accident, and it would probably be best not to jump to conclusions, or are you suggesting the whole rail network needs to close down in this year's hot weather?