A rack-and-pinion track design used on extreme mountain grades to prevent locomotives from slipping. It uses two or three parallel steel rack rails mounted between the running rails, with their teeth staggered. This offset ensures that at least one pinion gear on the locomotive is fully engaged with a tooth at all times, providing continuous traction and preventing the jerking motion common to older single-rack designs.
Heard on the job
They had to lay an Abt system on the upper division to get the tourist trains up that 16 percent grade safely.
Insider tip
Because the teeth are offset, locomotives built for an Abt system require synchronized, multi-pinion drive gears that cannot operate on other rack profiles.