Editing Rack railway (section)

== Rack-and-adhesion or pure-rack ==
[[File:Abt traction transition.JPG|thumb|right|Traction transition section]]

As well as the rack system used, lines using rack systems fall into one of two categories depending on whether the rack rail is continuous or not. Lines where the rack rail is continuous, and the cog-drive is used throughout, are described as pure-rack lines. Other lines, which use the cog drive only on the steepest sections and elsewhere operate as a regular railway, are described as rack-and-adhesion lines.

On rack-and-adhesion lines, trains are equipped with propulsion and braking systems capable of acting both through the running rail wheels and the cog wheels, depending on whether the rack rail is present or not. Rack-and-adhesion lines also need to use a system for smoothing the transition from friction to rack traction, with a spring-mounted rack section to bring the pinion teeth gradually into engagement. This was invented by Roman Abt, who also invented the Abt rack system.<ref>Roman Abt, Rack-Rail for Railways, {{U.S. Patent|349,624}}, September 21, 1886.</ref>

On pure-rack lines, the train's running rail wheels are only used to carry the train and do not contribute to propulsion or braking, which is exclusively done through the cog wheels. Pure-rack lines have no need of transitioning systems, as the cog wheels remain engaged with the rack rail at all times, but all track, including sidings and depots, must be equipped with rack rail irrespective of gradient.