I have written extensively about this subject on previous threads, so will only summarise here.
The issue for CWR, which is almost all the rail on the network, is the difference between the Stress Free Temperature of the rail (ie the temperature at which the rail has no compressive or tensile forces acting on it, given that CWR is in a fixed position), and the actual temperature of the rail. The actual temperature of the rail is a function of the air temperature, and exposure to sunlight. Today, with air temperatures of 26C, rail temperatures in sunlight will be 45C +.
The Stress Free temperature (SFT) in this country is normally 27C. In other countries it is different.
Rail can cope with temperatures around 30C above the SFT, as long as the track bed is not disturbed. Above that there is a significantly increased risk of buckles. However anywhere there has been recent trackwork causes the track bed to lose its rigidity, and along with several other factors this means the 30C limit above the SFT will be reduced. Furthermore, if new rail is installed and is not at the SFT of 27C, then the rail temperature that risks buckles can be much lower. For example I once imposed a ‘Heat Speed’ in the middle of February: the rail was installed at -5C and not stressed, on new ballast, then the sun came out and we had a rail temp of 17C IIRC.
As a rule, heat speeds *for track* only go on For one of three reasons:
1) recent work to the track, leading to the SFT being lower than normal (it can be much lower)
2) some types of defects in the track, which are judged by the relevant engineer to lead to an increased risk of buckles in hot weather
3) incomplete records of SFT.
I don’t know what has happened on the GWML.
There is also the issue that if there are several heat speeds in close proximity, it becomes difficult to provide boards for them (and multiple restrictions may cause confusion for drivers), hence the application of ‘blanket’ speeds covering a wide area.
If the Gov gets its way and defeats the RMT then expect more of these restrictions as maintenance etc is cut back on......
rubbish. Please stop spreading false information.
They also use inferior grade steel except on the high-speed lines
No ‘they’ don’t. It’s the same steel - indeed the rails used on some French High Speed line is made in Scunthorpe, on the same prodcution line, with the same steel, as is used on NR.
The difference on high speed lines is that a heavier section of rail is often used. This is also the case on heavy freight lines, eg in the US and Russia.
If normal summer weather conditions cause major problems for the railway, that is poor. Is there any other industry or infrastructure that gets so perturbed by average conditions?
Yes, aviation, maritime, etc etc.
They have every sort of rail, from immaculate cwr to dilapadated sidings, but none are impacted by temperature change.
Yes they are. The laws of physics are universal!
They simply accept more buckles in summer, more rail breaks in winter, run at lower speeds anyway, and in some extreme cases they restress the rails in autumn and spring.