What is "gravity railroad"

A gravity railroad ( American English) or gravity railway ( British English) is a railroad on a slope that allow 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 or a stationary engine and a cable, a chain or one or more wide, flat iron bands. A much later example in California used 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States, the Mauch Chunk & Summit Hill Railroad, which remained in operation for decades as a tourist ride after it was withdrawn from freight service hauling coal.