OPERATORS and Network Rail have warned that some trains are likely to run more slowly than usual as rail temperatures climb this week.

The first prolonged spell of warm weather so far this summer could see temperatures reach 28 C in south east England by Thursday.

Andy Thomas, the managing director of England and Wales at Network Rail said: “On very sunny days, rails in direct sunshine can be as much as 20 degrees centigrade above air temperature causing the steel to expand markedly and could, if not carefully monitored and action taken, buckle causing travel disruption.

“Our engineers and specialist extreme weather teams are monitoring track-side temperatures and vulnerable locations and will, if necessary, introduce temporary speed restrictions during the hottest part of the day to keep trains running, albeit more slowly than normal.”

GWR suburban services in the Thames Valley are among those which could be affected, particularly after midday until about 20.00, while South Western Railway services from London Waterloo are also being slowed down as far as New Malden.

GWR operations director Rob Mullen said: “We know how important it is that we run trains on time, but for the safety of all, we will have to run some services at reduced speeds during the hottest parts of the day this week – and this will cause some short notice delay or cancellations.”

Network Rail paints vulnerable rails white, which reflects the sunlight and reduces track temperatures by as much as 10 degrees.

Daytime temperatures in the London area are expected to stay in the higher 20s celsius until early next week.

We have 28 degrees forecast for later this week in parts of southern England, but this region can also experience temperatures well below freezing in a cold winter, with minus 10 by no means unknown.

As summer temperatures in the south can (and do) hit 30 or more, the possible range is at least 40 degrees Celsius, and rails must be manufactured to suit this as far as possible (the optimum which is 'built in' is 27 degrees). However, rail temperatures can be 20 degrees higher than the air temperature, so the rails could be close to 50 degrees this week. Starting at minus 10, that's a potential range of 60 degrees (rails) and 40 degrees (air).

Such ranges are not unique to Britain by any means, but they tend to be less extreme in hotter countries. The mean temperatures in Abu Dhabi, for example, go from 17 to 42, which is a range of 25 degrees (although the rail temperatures could of course be higher in peak summer). One further point is that the rails very rarely cool off enough to reach freezing point, and so rails intended for the Middle East can be manufactured accordingly.

Ironically, then, rail temperatures can be a greater problem in temperate countries, particularly those which experience many degrees of frost as well as comparatively hot summers.