Without a mountain railway system, on steep grades, gravity can apply sufficient translating force on the locomotives' wheels to overcome the friction between the wheels and the rails, and the locomotive will simply slide down the track. Ordinarily, railway locomotives require grades no steeper than 1 in 40 (21/2%)for practical operations. While ordinary railway locomotives can operate on grades as steep as 1 in 30 (31/3%), their hauling capacity is limited and more powerful locomotives are normally required. Traction rail systems can easily operate on grades as steep as 1 in 12 (81/3%), a grade that challenges all but the lightest locomotives or railcars.
On very steep grades cables are used because they are stronger than the normal railway couplings between the railway cars. The car itself is often custom built for the slope, with specially raked seatin and steps rather than a sloped floor. Taken to its logical conclusion as the slope becomes vertical, a funicular becomes an elevator (British English: lift).
Mountain Railways in England
Mountain Railways in Scotland
Mountain Railways in Wales
Mountain Railways on the Isle of Man
Mountain Railways in Germany
Mountain Railways in Switzerland
Historic Mountain Railways in New Zealand