Trains and the heat

doogz84

The thread about guitars and the heat, and something I read on the BBC earlier got me thinking.

There was an article about trains running at slower speeds, as they're worried about portions of track buckling.

I can only assume this would occur as a result of thermal expansion.

Which is really an issue, not of outright peak temperature, but of the range of temperature, yeah?

Either way, there are places on earth where trains run in higher temperatures, or with a higher range of temperature throughout the year, than we deal with in the UK.

So, what gives? What's this all about?

JezWynd

Possibly because when they set the tolerances for the track they didn’t think that UK would experience temperatures the like of which we are seeing.

ESBlonde

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Modern rails are welded and don't have many expansion gaps so that high speed trains can use them at speed - except when they can't!

The good news is that fewer trains means those that run will be even more crammed and the customers even more uncomfortable. (I must try to be less cynical in my old age).

doogz84

ESBlonde said:

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Modern rails are welded and don't have many expansion gaps so that high speed trains can use them at speed - except when they can't!

So do they have these sorts of issues on a hot day in say, Japan, then?

I kinda doubt it.

m_c

My understanding of it, is tracks are regularly cut and rewelded to allow for temperature change. The problem comes when there is a sudden rapid change, and the inspection/welding crews can't keep up.

There are expansion joints, but some segments can be several miles long, so seasonal adjustment is still needed.

I suspect in countries that see bigger temperature changes they rely on more expansion joints.

thecolourbox

doogz84 said:

ESBlonde said:

/|\

Modern rails are welded and don't have many expansion gaps so that high speed trains can use them at speed - except when they can't!

So do they have these sorts of issues on a hot day in say, Japan, then?

I kinda doubt it.

Where is the money going to come from to replace all our rail tracks with modern technology? Our train tracks were probably built over a century ago so of course more recently built Train systems will have better adaptability

doogz84

m_c said:

My understanding of it, is tracks are regularly cut and rewelded to allow for temperature change. The problem comes when there is a sudden rapid change, and the inspection/welding crews can't keep up.

There are expansion joints, but some segments can be several miles long, so seasonal adjustment is still needed.

I suspect in countries that see bigger temperature changes they rely on more expansion joints.

Interesting. Seasonal adjustment. Hadn't considered that as a real option, seems like a lot of work!

The videos of the engineers welding bits of track together are v.cool!

Matt_McG

According to the Guardian website, the rails are pretensioned before they are welded, to "set" them for a particular operating temperature range. 

So, as has already been written above, they can't just nip out and re-weld all the rails when a heatwave turns up.

Much like countries that get regular heavy snowfall have infrastructure designed for it, and we don't (because it's rare enough that it wouldn't be cost effective to gear up for it as business as usual).

VimFuego

you know what we need? Let me answer that in song:

https://www.youtube.com/watch?v=ZDOI0cq6GZM

Matt_McG

Bennie Railplane:

https://www.youtube.com/watch?v=vvSmwMqtylA

jonnyburgo

doogz84 said:

ESBlonde said:

/|\

Modern rails are welded and don't have many expansion gaps so that high speed trains can use them at speed - except when they can't!

So do they have these sorts of issues on a hot day in say, Japan, then?

I kinda doubt it.

I’ve been in Japan in the height of summer and they were there on time to the second. If a train is late in Japan and you’re going to work they give you a late pass on the train to give to your boss when you get to work. I’m sure they’re not needed often.

exocet

50 cms expansion per Kilometre of rail length was quoted this morning on the radio. They design for "Typical UK temperatures" and have issues when that range is exceeded.   Thing is, France has a wider temp delta than UK - it's colder in Winter and Warmer in Summer so how do they cope?

thecolourbox

exocet said:

50 cms expansion per Kilometre of rail length was quoted this morning on the radio. They design for "Typical UK temperatures" and have issues when that range is exceeded.   Thing is, France has a wider temp delta than UK - it's colder in Winter and Warmer in Summer so how do they cope?

Presumably they were also built after ours so better knowledge and tech

scrumhalf

When there was a lot more freight on the railways the tracks were maintained to a far more robust standard. Passenger traffic causes less stress than freight traffic and I would imagine that the tracks are maintained to a lower standard.

thecolourbox

I'm too young to know this as they've always been privatised in my lifetime, but did we have these problems before the railways were privatised?

I know the volume of trains and passengers was probably less so may be a moot point but thought worth an ask

scrumhalf

thecolourbox said:

I'm too young to know this as they've always been privatised in my lifetime, but did we have these problems before the railways were privatised?

I know the volume of trains and passengers was probably less so may be a moot point but thought worth an ask

Before privatisation British Rail were quietly pushing in the background for freight to be taken off the rails. It wasn't hugely cost-effective, the track needed to be maintained to a higher standard and passenger trains were being held-up by slower-moving freight services which were less profitable than passenger services.

crunchman

thecolourbox said:

I'm too young to know this as they've always been privatised in my lifetime, but did we have these problems before the railways were privatised?

That was getting on for 30 years ago.  There were a lot more joints in the track back then.  Joints allow room for expansion.

The big problem is that rails in direct sunlight get a lot hotter than the surrounding air.

I suspect that countries with bigger ranges of temperatures will have more expansion switches.  The downside of that is that the expansion switch is a weakness in the rail, and can cause track geometry issues.  It will also increase maintenance costs, as more frequent expansion switches will mean more sites to check the stress of.

I've read that Network Rail are now setting the Stress Free Temperature at 50C instead of 27C for new sites.  That will help massively in this kind of weather.  The downside is that there will be more tension in the rail at lower temperatures.  That will increase the risk of cracks and breaks in the rails.  With modern ultrasonic testing of the rails, that's probably a safer option than the risk of buckles, but again may cost extra as it might lead to an increased frequency of ultrasonic testing.

57Deluxe

So it seems HS2 is even more implausible what with climate change doom imminent...?

crunchman

57Deluxe said:

So it seems HS2 is even more implausible what with climate change doom imminent...?

HS2 will be built (and maintained ) to much higher standards.

I know on LU that it's the old clapped out track that we tend to have issues with movement.  With Khan's fares freeze, there will be more old clapped out track in 10 years time than there should be.

siremoon

The reason that overseas railways with higher temperatures don't have problems in unusually hot weather is because their track is specified to cope with it as it is an expected and regular occurrence.  That means larger rail cross section, closer sleeper spacing, different ballast profile etc.  That uses more materials and is harder to handle during installation as there is more weight etc so it costs more.

Also maintenance and inspection now is far more automated than it was.  In the past all track was manually inspected, maintenance was far more labour intensive and thus there were far more staff available to patrol on hot days looking for signs of buckling.  H&S restrictions on track access and the imperative to cut costs through automation mean that is no longer the case.  Local staff also knew the weak spots on their patch so they knew where to look.

The other problem on very hot days is the expansion of the overhead line contact wire.  This has to be kept in tension and if it isn't then the trains bring it down.  This happened at several places yesterday.  Typically this is a function of both the age of the equipment and the design of the support equipment.  Older equipment either has no temperature compensation at all (most of this has been replaced - there is still a little bit on the lines out of Liverpool St) or it is relatively crude (but adequate for typical UK temperature ranges).

In the 1950s and 1960s BR electrification schemes used rugged support gantries which were ugly but have stood the test of time but in the 1970s and 1980s BR changed to a system called headspans for new work.  This replaced the horizontal metal girder or lattice structure on a conventional gantry with a cable assembly.  This was less visually intrusive and cheaper.  However if the cable assembly expands too much then the contact wire alignment is lost and the lot comes down.  This happened on both the ECML and MML yesterday (which are the two major main lines out of London with large numbers of headspan structures).  Headspans are no longer used for new work and there is a program to replace them in a number of areas however that is time consuming, expensive and disruptive.

There are engineering solutions to prevent everything which happened yesterday but historically it wasn't considered cost effective to engineer for occasional extremes however the major routes are being upgraded to a higher specification as part of routine renewals or specific programmes such as headspan removal.  Of course the public don't like upgrade work either though (see the adverse coverage in the media at Christmas etc when lines are closed for work). 

TTony

crunchman said:

HS2 will be built 

Not so sure about that ...