What s a rack railway?
From Larry Pieniazek: ! Rack railways are also called cog railways. In addition to the two weight bearing rails there is a central toothed rack that a cog on the power car engages. When the limits of adhesion are reached during the ascent (typically around 5% grade or so) the cog engages and powers the ascent. Similarly on descent, the cog takes the primary braking load.