Trains can face speed restrictions or reduced operating speeds in extremely hot weather due to a phenomenon known as "heat kinks" or "sun kinks." This is primarily applicable to railroad tracks made of steel.
When the ambient temperature rises significantly, the steel tracks can expand due to thermal expansion. If the tracks are not properly supported or restrained, this expansion can cause the tracks to buckle or warp, resulting in irregularities or deformations known as heat kinks. These deformations can pose a safety risk and can lead to derailments if trains travel over them at high speeds.
To mitigate this risk, railway operators often implement speed restrictions during hot weather to reduce the stress and strain on the tracks. By lowering the speed of the trains, the forces exerted on the tracks are reduced, minimizing the likelihood of heat kinks occurring.
Additionally, high temperatures can also affect other components of the rail infrastructure, such as overhead power lines, signaling systems, and trackside equipment. Extreme heat can cause electrical systems to malfunction or overhead lines to sag, which can further impact train operations and safety.
Overall, the limitations on train speed during hot weather are primarily in place to ensure the safety and integrity of the railway infrastructure and to mitigate the risks associated with thermal expansion and related phenomena.