Gravity railroad

A gravity railroad (American English) or gravity railway (British English) is a railroad on a slope that allows cars carrying minerals or passengers to coast down the slope by the force of gravity alone. The speed of the cars is controlled by a braking mechanism on one or more cars on the train. The cars are then hauled back up the slope using animal power, a locomotive or a stationary engine and a cable, a chain or one or more wide, flat iron bands. A much later example in California used 4 ft 8+1⁄2 in (1,435 mm) standard gauge steam engines to pull gravity cars back to the summit of Mt. Tamalpais.

The typical amusement park roller coaster is designed from gravity railroad technology based on the looping track incorporated into the second railroad of the United States, the Mauch Chunk and Summit Hill Railroad, which remained in operation for decades as a tourist ride after it was withdrawn from freight service hauling coal.

A variation is the railway gravity yard or hump yard. This is a goods yard incorporating a "hump" gradient: it allows a single goods train to be taken slowly over the hump, with the wagons sequentially detached and allowed to roll downhill into an array of different sidings: timely operation of the railway points chooses which siding each wagon ends up in. This allows a single train to be speedily disassembled and the wagons sorted into new goods trains, without the need of a shunting engine.

In a further variation, a slip car or slip coach was a section of coaches at the end of a train that had a different destination to the main train: these rear carriages could be uncoupled at speed, diverted onto a different set of tracks by operating the railway's points, and would then proceed to their separate destination, using a combination of gravity and momentum, without a locomotive, and controlled by the brakes operated by the guard in the rear guards van.