hump yard
a classification yard or marshalling yard which has a hump over which trains are shunted, the vehicles then running on their own by gravity into various sidings.
hump yard: gravity-fed rail classification using a slope
A hump yard is a rail classification facility built on a slope, where freight cars are pushed up and over a raised section of track, then allowed to roll by gravity into sorting sidings below. The "hump" is typically 40 to 50 feet high, and the cars separate as they descend, guided by switches that direct each vehicle to its assigned track. This design eliminates the need for engines to shunt every car individually across the yard, cutting coupling and decoupling labor dramatically.
The process begins with arriving trains placed on the lead track. A yard engine couples to the train and hauls it upgrade toward the hump crest. As cars crest the summit and begin their descent, workers or automated systems throw switches to direct them into the correct classification sidings. Cars roll under their own momentum, slowing as they travel downgrade and eventually couple with others of the same destination.
Retarders and speed control
Without friction management, cars would reach dangerous speeds. Modern hump yards employ retarders, which are track-mounted devices that apply dynamic braking or friction to slow rolling cars to 3 to 6 miles per hour before they reach their sidings. Older yards relied on manually operated wheel brakes or friction switches; newer installations use hydraulic or electromagnetic retarders controlled automatically based on car weight sensors and destination.
Hump yards are most efficient at high-volume terminals handling 2,000 to 4,000 cars daily. Small branch lines and ports may use flat yards instead, where every movement requires engine power. The hump design suits large classification centers serving major rail routes, where consistent sorting of varied freight justifies the capital cost and infrastructure.
The term originated in the 1920s and 1930s when the first large gravity yards were built in North America and Europe. The hump itself is not a natural feature but engineered fill, often 800 to 1,200 feet long, built to provide sufficient grade for cars to roll freely. Hump yards remain the standard model for major freight classification despite the rise of computer-controlled switches and sensor networks.