The absolute highest point on a section of track, where an ascending grade transitions into a descending grade. Reaching this point is a critical milestone for heavy freight trains, as the locomotive engineers must immediately transition from pulling hard against gravity to applying dynamic and air brakes to control the descent.
Keep the power on until the rear end clears the summit, then start setting up the air for the downgrade.
A train cresting a summit is highly vulnerable to a broken knuckle or pull-apart if the head end starts rolling downhill while the rear end is still dragging up the grade.
Also heard as
- crest
Related terms
Helper grade
A section of track steep enough to require additional locomotives to push or pull trains over the summit.
Dynamic braking
Retarding force made by turning a locomotive's traction motors into generators and burning the energy off as heat.
Pull-apart
A break in the rail, usually at a joint or weld, caused by the rail shrinking in extreme cold.