What temperature is stressing rail?

In the United Kingdom, CWR is stressed to 27 °C (81 °F), the mean summer rail temperature. In the US, standard stress free temperatures vary from 35 to 43 °C (90 to 110 °F). Despite stressing the CWR before installation, a rail may still reach its Critical Rail Temperature (CRT).



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Because rails are made from steel, they expand as they get hotter, and can start to curve this is known as 'buckling'. Most of the network can operate when track temperatures heat up to 46°C – roughly equivalent to air temperature of around 30°C – but rails have been recorded at temperatures as high as 51°C.

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In the US, standard stress free temperatures vary from 35 to 43 °C (90 to 110 °F). Despite stressing the CWR before installation, a rail may still reach its Critical Rail Temperature (CRT). This is the temperature of the rail above which buckling may occur.

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Since the kinetic energy of the vehicle is transformed into heat energy via friction force, the most important deformations are heat related. The maximum temperature on the brake disc surface can reach almost 600 °C in a classic railway vehicle [11], [12].

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In hot weather, the overhead lines that provide power to the trains can expand and sag. To avoid damaging the lines, trains must travel more slowly. If the overhead lines are damaged, we have to cancel or divert train services until they are fixed. This causes delays.

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Just as people can suffer sunburn or heat stroke from too much exposure to sunlight and hot temperatures, rail can bend or warp because of a blistering sun and sweltering temps. If the rail malformations known as a sun kink or track buckle aren't repaired in a timely manner, trains can derail.

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This stress can cause railway steel to fracture. In extreme heat, a length of CWR suffers compressive stress. This type of stress can cause sun kink where a length of a railway buckles laterally (sideways).

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The mechanism of an emergency brake may differ, depending on railcar design. Emergency-braking a train (without track brakes) will give about 1.5 m/s2 (0.15 g) deceleration. The braking distance will be approximately 250 m (820 ft) at 100 km/h (62 mph) and 600 m (2,000 ft) at 160 km/h (99 mph).

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