Which trains will be affected by the heatwave?
Of course, many trains will lack ventilation and air conditioning, but there's more. Network Rail has imposed speed restrictions on some services, and in addition to that, they're advising that everyone checks their journeys before travelling.
A First Great Western spokesperson said: "Network Rail has advised that, due to the anticipated exceptionally hot weather, there will be speed restrictions to protect track points in the Thames Valley region on Tuesday 30 June 2015."
"As a result there will be no fast trains between London Paddington and Bourne End or Henley-on-Thames from 12pm until 8pm. Trains from London Paddington will terminate at Twyford for a connection with a branch line train to Henley-on-Thames, which will remain on the branch line."
"Trains from London Paddington will terminate at Maidenhead for a connection with a branch line train to Bourne End, which will remain on the branch line."
So what's going on? Why does a bit of sunshine cock things up? The spokesperson continued: "As rails are made out of steel, they expand as they heat up and are subject to strong compression. This expansion has to be managed to reduce the risk of track buckling."
"If the track does buckle, the line must be closed and the track repaired before services can resume, causing considerable disruption. Usually, these repairs can’t be done until the temperature of the rails has dropped."
"If a section of track is judged to be at risk, we introduce local speed restrictions – slower trains exert lower forces on the track and reduce the chance of buckling."
So there you go. Network Rail have even made a little video about it all too.
If you're unimpressed with any delays or cancellations, then you'd be wise to check out our guide to getting refunds and compensation for train journeys.