Steel rail contracts as the temperature falls, and on a bitter night the tension in welded rail can snap a weld or shear the bolts in a joint, leaving a gap of an inch or more. In signaled territory the break usually opens the track circuit and drops the signals to stop, which is how many pull-aparts are found. Track crews close the gap with a plug or by heating and pulling the rail back together.
Twenty below last night and the signal maintainer found a pull-apart at the east switch, that's why the board's red.
Also heard as
- pull apart
Related terms
Sun kink
A sideways buckle in welded rail caused by heat, which can throw the track out of line under a train.
Ribbon rail
Long strings of rail welded together end to end and laid without bolted joints.
Plug
A short piece of rail cut into the track to replace a section with a defect or a break.
CTC
Centralized traffic control: signals and switches controlled remotely by a dispatcher who routes every train.