https://www.networkrail.co.uk/stories/why-rails-buckle-in-britain/ https://www.networkrail.co.uk/stories/why-rails-buckle-in-br... says “rail can actually be up

https://www.networkrail.co.uk/stories/why-rails-buckle-in-britain/ https://www.networkrail.co.uk/stories/why-rails-buckle-in-br... says “rail can actually be up to 20 degrees higher.” and “For some of our track, such high temperatures are more than our track is designed to cope with”, so it depends on the track, but can be around 50°C. A rail that’s in the shade for most of the day will get less hot, so I expect location also influences at what air temperature track will buckle.