Why ordinary train wheels lose their grip
On a conventional railway, a locomotive moves because its powered wheels press against the tops of the rails. The small amount of friction at that contact can pull a train up a slope, but the steeper the track gets, the more gravity tugs the train backward. Eventually the wheels may slip, no matter how much power the locomotive can deliver.
A rack railway adds a separate way to transmit force. A toothed metal rail, called a rack, runs between the ordinary rails. A gear wheel, or pinion, beneath the locomotive meshes with its teeth. As the pinion turns, it pushes against the rack and advances the train uphill.
The track becomes part of the drive
The rack does more than help the train climb: it gives the locomotive something positive to engage with, rather than asking smooth wheels to find enough grip. The same engagement can help control the train on the descent, when gravity is pulling it forward. Brakes still matter, but the gear-and-rack system provides a mechanical connection to the track.
That connection requires specially built track and compatible vehicles. The pinion must meet the rack correctly, and the railway’s rails, gears, and braking systems must be designed for the steep route. A rack locomotive therefore cannot simply switch onto any ordinary line and climb a severe grade.
“Nearly vertical” describes the striking steepness such systems can handle, not a train traveling straight up a wall. The practical result is that a railway can tackle slopes that ordinary wheel-on-rail traction cannot manage—by turning the track itself into part of the locomotive’s machinery.
