# railway line thermal expansion **URL:** \ **Category:** Factual Questions\ **Created:** [July 5, 2004, 8:55pm UTC](https://boards.straightdope.com/t/railway-line-thermal-expansion/253690 "2004-07-05T20:55:15Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![InvidiousCourgette](https://avatars.discourse-cdn.com/v4/letter/i/e47c2d/32.png) [@InvidiousCourgette](https://boards.straightdope.com/u/InvidiousCourgette)\ **Post date:** [July 5, 2004, 8:55pm UTC](https://boards.straightdope.com/t/railway-line-thermal-expansion/253690/1 "2004-07-05T20:55:15Z")
in the old days, trains used to go clickety click. nowadays i don’t think that is so. so have they discovered a way to fix the expansion of metal? ---
**Author:** ![TheLoadedDog](https://avatars.discourse-cdn.com/v4/letter/t/35a633/32.png) [@TheLoadedDog](https://boards.straightdope.com/u/TheLoadedDog)\ **Post date:** [July 5, 2004, 9:08pm UTC](https://boards.straightdope.com/t/railway-line-thermal-expansion/253690/2 "2004-07-05T21:08:07Z")
There is no one answer to this. Trains don’t go clickety clack anymore 'tis true. Now they go “clickety … …clack”. The expansion joints are still there, but they’re further apart. A major component of this is simply having longer rails for passenger comfort and less wear and tear, and well… _just hoping for the best_. In the Australian summer there are always two or three incidents on the Sydney commuter network where buckled rail causes afternoon peak hour chaos as trains are delayed and diverted. Even when no damaged rail has been detected, extreme heat conditions mean special speed limits are introduced. In cooler climates, it’s not so much of a problem (though extreme cold can also do bad things to the track). Another trick is to have a more specialised expansion joint in which the gap runs from the outer to the inner edge on the railhead at a very shallow angle rather than straight across. This affords the wheel constant support so it won’t drop into the gap. As an interesting aside, the longest lengths of continuously welded rail in the world are found in Japan’s undersea rail tunnels where temperatures are at a cave-like constancy. ---
**Author:** ![Duckster](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/duckster/32/1244_2.png) [@Duckster](https://boards.straightdope.com/u/Duckster)\ **Post date:** [July 5, 2004, 9:13pm UTC](https://boards.straightdope.com/t/railway-line-thermal-expansion/253690/3 "2004-07-05T21:13:45Z")
One of the hottest places to install ribbon rail is in Australia. Here’s how they did it between Alice Springs and Darwin … > [@](#): > > **Older generation railway workers are adamant that you must have expansion joints otherwise the rail will buckle. How does the continuous rail overcome thermal expansion and contraction in the temperatures between Darwin and Alice Springs?** > > In order to balance the forces between those which want to buckle the track during high temperatures and those which want to pull the rails apart during cold temperatures the rail is layed at what is called the neutral temperature of 40 degrees Celsius. The range of rail temperature expected throughout the course of the year is approximately -10°C to +65°C. > > On a railway the length of the Alice Springs to Darwin railway (1420km) this movement would be 16.3 metres for every degree of temperature change. It has been calculated that the rails are subjected to a temperature range of 45 degrees in Darwin and 74 degrees in Alice Springs. This would mean that the rails would expand and contract up to 1.2 km between the coldest night and hottest day during the year. > > If the rail were free to move when heated or cooled it would expand or contract like all other steel. A small amount of the stress developed along the rail can be taken up with expansion across the rail. Its height and width expand due to their own dimension as well as some distributed stress from the longer length. The rail bulges slightly. As long as the column is prevented from moving sideways along its length it is very stable. Source: [http://www.aarc.com.au/aarc/info/factsheets/rail\_welding.htm](http://www.aarc.com.au/aarc/info/factsheets/rail_welding.htm) ---
**Author:** ![GorillaMan](https://avatars.discourse-cdn.com/v4/letter/g/50afbb/32.png) [@GorillaMan](https://boards.straightdope.com/u/GorillaMan)\ **Post date:** [July 5, 2004, 9:42pm UTC](https://boards.straightdope.com/t/railway-line-thermal-expansion/253690/4 "2004-07-05T21:42:23Z")
> [@TheLoadedDog](#): > > A major component of this is simply having longer rails for passenger comfort and less wear and tear, and well… _just hoping for the best_. I think this rather trivialises the great attention paid by engineers to rail safety. Simply, Continuous Welded Rail (CWR) requires the rail to be installed at precisely the right temperature, in comparison to local climate considerations. Without the technology to do this reliably, it was impossible. Nowadays, this technology is commonplace, so CWR is perfectly safe. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [July 5, 2004, 10:55pm UTC](https://boards.straightdope.com/t/railway-line-thermal-expansion/253690/5 "2004-07-05T22:55:34Z")
From [Wikipedia](http://en.wikipedia.org/wiki/Rail_tracks): > [@](#): > > … rails expand in hot weather and shrink in cold weather. Because welded track has very few expansion joints, if special measures are not taken, it could become distorted in hot weather and cause a derailment. > > To avoid this happening welded rails are nearly always laid on concrete sleepers, which are so heavy they hold the rails firmly in place. Soon after the segments of rail are laid, the rails are artificially heated to normal summertime temperatures so that they expand, they are then quickly fastened tightly to the sleepers in their expanded form and then welded to the next segment of rail, this ensures that the rail will not expand any further in subsequent hot weather. And because they are firmly fastened to the sleepers, they cannot shrink in cold weather either. However if temperatures reach outside normal ranges (i.e a hotter than usual summer), it can cause problems with welded rails. ---
**Author:** ![TheLoadedDog](https://avatars.discourse-cdn.com/v4/letter/t/35a633/32.png) [@TheLoadedDog](https://boards.straightdope.com/u/TheLoadedDog)\ **Post date:** [July 5, 2004, 11:01pm UTC](https://boards.straightdope.com/t/railway-line-thermal-expansion/253690/6 "2004-07-05T23:01:40Z")
> [@GorillaMan](#): > > I think this rather trivialises the great attention paid by engineers to rail safety. Simply, Continuous Welded Rail (CWR) requires the rail to be installed at precisely the right temperature, in comparison to local climate considerations. Without the technology to do this reliably, it was impossible. Nowadays, this technology is commonplace, so CWR is perfectly safe. This technology is still very new. But the very short-length rail hasn’t been around since the days of steam. So what happened in the interim? Well, much longer rail length (hundreds of feet) was laid using relatively old tech. In the last thirty years, whenever a rail buckled, the oldtimers would start saying how it never happened in their day. I think there really was an element of just hoping it wouldn’t happen, and glossing over it when it did. CWR may well change that, but at least where I live, there’s not much of it around yet. ---
**Author:** ![GorillaMan](https://avatars.discourse-cdn.com/v4/letter/g/50afbb/32.png) [@GorillaMan](https://boards.straightdope.com/u/GorillaMan)\ **Post date:** [July 5, 2004, 11:33pm UTC](https://boards.straightdope.com/t/railway-line-thermal-expansion/253690/7 "2004-07-05T23:33:24Z")
“Very new”? The first CWR was laid in 1937. It was being installed across the UK in the 60s and 70s. Not much newer then than, oh, electric trains? ---
**Author:** ![TheLoadedDog](https://avatars.discourse-cdn.com/v4/letter/t/35a633/32.png) [@TheLoadedDog](https://boards.straightdope.com/u/TheLoadedDog)\ **Post date:** [July 6, 2004, 1:31am UTC](https://boards.straightdope.com/t/railway-line-thermal-expansion/253690/8 "2004-07-06T01:31:07Z")
Well, I guess it depends how continuous “Continuous” is. I can remember as a kid in the 70s when rail of about 200 - 300M in length was laid, people were marvelling at it. And yes, it was on wooden sleepers. Some of it was even held down with ye olde DOG SPIKE in places, though this was rare. However the clips they used (even on concrete sleepers which first started appearing in the 80s here) are diferent from the design used today. On the journey I’m about to take in an hour’s time, there is a variety of track, with concrete sleepers only present on about 70 - 80% (WAG) of it, and the new design of clip on about half. And yes, there is the familiar _da dum da dum_ as we go along - just not as much as there once may have been. I think we’re talking about two different things. Yes, they’ve been welding bits of rail together for donkey’s years, but the technology of 2 000 KG pressure clips and welded rail to the horizon seems pretty new, at least in this part of the world. I remain convinced all the references I’ve seen are to a second generation CWR technology. I think before then, it was just called “welding bits of rail together”. That’s why they’re making such a big song and dance about it. ---
**Author:** ![Oat1957](https://avatars.discourse-cdn.com/v4/letter/o/bbe5ce/32.png) [@Oat1957](https://boards.straightdope.com/u/Oat1957)\ **Post date:** [July 6, 2004, 2:28am UTC](https://boards.straightdope.com/t/railway-line-thermal-expansion/253690/9 "2004-07-06T02:28:31Z")
Amtrak in the Northeast corridor lowers the speed limit of it’s trains when the temperature reaches 95° due to the “warping” of the welded rail. > [@](#): > > “We know the heat is a possible factor. Heat can cause a slight misshaping or a buckling in the rail,” said NTSB Vice Chair Carol Carmody. “We’re viewing this as an accident.” From http://www.disasternews.net/news/news.php?articleid=1509