How do rail tracks buckle in hot weather? By John Linkin

Rail passengers in the SE of England are facing disruption through speed restrictions amid fears that tracks could buckle under the current high temperatures.

Historically 18m (60ft.) rails with expansion gaps and joined with bolted fishplates regularly greased was commonplace until the 1950s.

Today, most routes where speeds are high and curvature reasonably flat, continuously welded rail (CWR) is now used.Rails are delivered and installed in 180m lengths (or greater) and then welded into even longer lengths on site.There can be many kilometres of rail without a single joint.

The science was developed and adopted by British Rail in the 50’s and 60’s with in depth investigation of the median temperature of rail in situ in varying locations such that, for an even proportion of the time, it would be in tension (cold weather) and then in compression (hot weather).This would restrict the maximum lateral forces that could be resisted by a combination of heavy concrete sleepers, robust rail fastenings to restrict longitudinal movement and heaped up ballast shoulders on the ends of the sleepers. The strength of rail welds was also a limiting factor for tensile stresses in cold weather.

 Buck rail

The mid temperature chosen was 27° Celsius.  This has largely proven to be a robust choice although recent national higher temperatures may indicate that there is reason for a revision of that figure.

The rationale for the nationally applied speed restrictions in very hot weather is to restrict the disturbance to the tracks and the additional lateral forces by higher speed trains which can result in buckles.

John Linkin - Rail Infrastructure Engineer 

John Linkin, Rail Infrastructure Engineer

John worked for British Rail for 25 years managing rail infrastructure renewals an maintenance in SE England including opening the Channel Tunnel and clearance for running Eurostar & freight over existing lines. Since then, he was worked on major rail projects throughout the world.

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