Rack railway technology
Steel wheels on steel rails grip about as well as a shoe on ice. Here is how engineers taught trains to climb slopes steeper than a staircase, and the people who worked it out.
Drag to make the hill steeper. Past about 7 % a normal train gives up; the rack takes over.
A rack railway lays a toothed bar between the rails and gives the engine a gear wheel, a pinion, to climb it. The idea is simple. Making it work on a real mountain, in snow, round curves, through points and safely back down again, took a century of invention by a handful of remarkable engineers.
Each chapter below has something to try. The models use real dimensions from the engineering papers of the day, and the railways in the last chapter are rebuilt from survey data so you can drive them yourself.