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Buckling of CWR in hot countries

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11 February 2014, 7:48pm

It is very important to ensure the rails are securely fastened to the sleepers. Single rails buckle easily, but when rigidly joined to the opposite rail, form a much more stable structure.

I have a little experience of heavy freight track in the Mexico City area (is this hot and variable enough?). Here track was being laid with no breathers (except to protect S&C), on concrete sleepers, with resilient fastenings and plenty of clean ballast. No problems reported.

Michael Simmers

18 February 2014, 2:44pm

In the Northeast US we use track buckling counter measures (a series of standards and procedures) to prevent track from buckling - Temps in the summer reach 100+F and -5F in the winter with temp swings of 40 degrees in a 8 hr time period. Typically most main line tracks (class 1 freight and Amtrak) use CWR without expansion joints or breather switches - our tracks may run several miles before encountering a points and crossing

- Tracks are installed and adjusted/destressed to a rail neutral temerature of about 100 F

- Tracks use resilient fasteners, wood or concrete sleepers, full ballast sections (12" /304mm shouolders and full cribs)

- Ballast needs to be clean, and track surface properly maintained

- Attention is given to ensuring that track re-profiling does not change the rail neutral temperature

- During period of extreme heat (temps exceeding 95F) some railways impose speed restrictions and/or use inspectors to monitor the track for signs of thermal expansion/movement - such as wavy rail or indications the sleepers have started to move horizontally -           

This is a brief description of the process..... 

Patrick Fenlon (Guest)

04 April 2014, 11:24am

The most important element is the adoption of a stress free temperature which should take account of the general/average conditions met.

I was the PWE for KCRC (Hong Kong) where the whole railway was fully welded for its' whole 20 mile length without any adjustment switches. I spent two years on re-ballasting the railway which left approximately 500m with reduced stability, by use of a DTS and double tamping the track was unaffected. In addtion, KCRC had a gross tonnage of 60 million/year which meant consolidation was achieved in a matter of days

In Thailand due to the length of the country there was three stress free temperatures adopted.

As said before maintenance of ballast profiles is a major key to the stability of the track.

David Cooper

15 July 2015, 4:17am


The key component in NSW is meticulous rail adjustment at installation and ongoing maintenance of design position.

This is met by engaging a dedicated survey competence to establish any track movement, and SFT loss is calculated at critical or suspected defficient locations.

Most installations are naturally stressed to 35 (max 38) Degrees Celsius, although we do apply tensors occasionally.

Ballast shoulders in fact, have a lesser requirement than GB in that the width is less and there is no heaped shoulder above top of sleeper.

95% of the Sydney Metropolitan network is heavy duty concrete sleepers. Even category 5 country infrastructure on timeber is well managed with essentially no issues for the past two years. There was one incident, which was proven to be ineffective management of rail adjustment.

Effective managment of critical rail temperature is THE major constituent to the fact we have very few, even minor rail misalignments, despite ambient temperatures up to 46 degrees.

David Cooper

A/Lead Engineer - Track Engineering, Transport for NSW

Constantin Ciobanu

01 October 2015, 1:36pm

The track buckling happens in hot weather because of a few factors but it is massivelly influenced by the track longitudinal and lateral resistance. Both these resistances have three levels of action:

between rail and fastening - at this level all the modern fastenings are behaving very well if they obey to the limits established by the fastening design norms - EN 13481 in Europe and asimilated arround the world due to the Europe-based main fastening providers - Vossloh and Pandrol. For modern sleepers the bucking will never happen at this level, the rail wont unclamp itself from fastenings and buckle. So using modern fastening is a method to avoid buckling.

between fastening and sleeper - here we encounter the highest resistance. For Pandrol fastclips the clip shoulder is casted in the sleeper's concrete so no relative movement of any kind will happen at this level. The alternative, screwed fastening, is similarly good and all modern screwed fastenings are design to have a very high lateral resistance at this level. Again - modern fastenings.

- between (rail+fastening+)sleeper and ballast - here the lateral and longitudinal resitances are the lowest and the most difficult to control. The bucking ALWAYS happens at this level - the rails/sleepers frame moves in the balast to look for the post-buckle equilibrium state. Hence, the most of the methods to mitigate the buckling risk are focused on increasing the resistance at this level.

A few ways to do this are:

a. increase the ballast inner resistance and it's interraction with the sleeper

- no ballast interventions in hot weather

- use of the dynamic track stabilisation machine

- glue balast (yucksmiley-undecided.gif! but it works!)

- increase the ballast shoulder dimensions

- use of lateral resistance plates

b. change the sleeper or improve its interaction with the ballast

- bigger/heavier sleepers - for some special sites in Germany is used a so called "wide sleeper" 

- H shape sleepers 

- Y shape sleepers

- under/lateral sleeper pads specially designed for increased lateral resistance 

- etc - lots of ideas

c. change the track superstructure

- slab track - buckle this if you can!

- heavier rail - able to take increased axial stress. Hmmm, what about different rail shape, one with a bigger lateral inertial momentum ...

Other things that can and should be done:

improve the general track quality 

- clean ballast

- well installed and maintained tracks without alignment deffects that could trigger the buckling. 

- good formation - with low variation between loaded and unloaded track to avoid buckling under trains. Arround the world it is used in the formation design/maintenance Ev2 as a measuring feature indicating the general stiffness of the formation.

trick the weather 

- if the temperatures are very high just install the rails at higher temperature to reduce the variation from neutral temperature to the maximum. The Russians are using this method - so called "summer rails" and "winter rails". Before summer, increase the track neutral temperature by reinstalling the track and in autumn, cut them and reinstall again at lower RNT, to prepare them for the heavy winter.

- paint them white ... 3 to 7 degree reduction in rail temperature sometimes helps ( a very interesting article about this you can find here: ).

Philip Dooner

02 March 2019, 2:25pm

In KSA, on the SAR network, the sleepers are of a heavier section and the SFT is higher, otherwise the management of CWR is very similar to the measures adopted in the UK. The network is entirely welded, with no adjustment switches or mchanical joints. I have noticed that an HSM70 struggles to close the gap when restoring stress in short rails, with the cut-off valve, which protects the pump, activating before the full extension is achieved.

Kevin O'Meara

16 March 2019, 3:45am

it depends where you are located and what your SFT is. i work in the pilbara Western Australia where temprature are high and the SFT is need to be 42C +/- 2C. It also depends on gemotretry and usage ie freight light rail or heavy haul. there is many techniques that can be used to manage stress like:

- Monitoing and verse testing.

- Installation of breather switches

- Increase ballast on shoulders.

- Reduce sleeper spacing.

- Install Hytel pad are high friction sleeper pads

- Place procedures to limit the affect on stress i.e no tamping below or above a rail temperature.

Ben Ghodrati

15 April 2019, 8:34pm

During hot weather in the UK, we apply white paint to switches particularly when they are tip to tip switches and when they have not been subject to any stressing. 

Glenn Melvin

13 September 2019, 8:57am


Are you able to share a standard or specification for the paint used. I have seen this used in many locations in the UK and Europe on main line railways but not yet used on metro systems as far as I am aware.

Pete Horan (Guest)

25 September 2019, 10:30am

Hi All,

I would like to echo Glenn's quirey regarding painting rails white to reduce rail temp. Has anyone come across a study or acedeimic paper that has proven this and quantifys the expected drop in temp that painting rails white can cause.

Constantin Ciobanu (Guest)

25 September 2019, 12:56pm

Here is a research paper presentated at an AREMA conference, in 2014.

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