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.

Trains and rail infrastructure are significantly affected by both extreme heat and extreme cold, but the most disruptive phenomenon is "Sun Kinks" (track buckling), which typically occurs when ambient temperatures rise above 30°C (86°F). Because steel rails are welded together, they expand as they heat up; if the heat is intense and prolonged, the internal stress can cause the rail to physically bend or "buckle" out of alignment. To prevent derailments in 2026, rail networks often impose "Temporary Speed Restrictions" during heatwaves. Conversely, extreme cold—typically below -15°C (5°F)—can cause "pull-aparts," where the steel contracts so much that the rail snaps or the joints fail. Cold weather also affects the mechanical components of the trains themselves, such as frozen air brakes or brittle electrical cables. For high-speed rail, even moderate temperature fluctuations can be problematic, as the high-precision tracks are sensitive to any expansion. Consequently, modern rail operators constantly monitor rail temperatures—which can be 20 degrees hotter than the air—to adjust speeds and maintain safety.