Continuous welded rail is anchored at a chosen neutral temperature, the rail temperature at which it carries no lengthwise stress. On hot days the rail expands with nowhere to go, and if the compressive force beats the grip of ties and ballast, the track snaps sideways into an S-shaped kink, sometimes right under a passing train. Railroads issue heat slow orders and patrol the worst spots in hot weather to catch them before a derailment.
Engineer of the stack train reports a sun kink at MP 141, track's out of line about 6 inches, stop everything.
Track people care about rail temperature, not air temperature, and rail in full sun runs 20 to 30 degrees F hotter than the air around it.
Also heard as
- heat kink
- track buckle
- buckled track
Do not mix it up with
- Pull-apart: A pull-apart is the cold-weather opposite: the rail shrinks and breaks instead of expanding and buckling.
Related terms
Ribbon rail
Long strings of rail welded together end to end and laid without bolted joints.
Pull-apart
A break in the rail, usually at a joint or weld, caused by the rail shrinking in extreme cold.
Slow order
A temporary speed restriction on a stretch of track because of its condition, heat or work in progress.
Ballast
The bed of crushed rock under and around the ties that holds the track in line and drains water away.