How it works
- Build the cut: A switching locomotive couples a group of cars and pushes them up the approach to the hump.
- Crest & uncouple: At the summit, a yard operator (or automation) uncouples single cars or blocks so they roll freely.
- Route: Power-operated points set each car’s path toward the correct classification track—called the bowl.
- Control speed: Trackside retarders grip the wheels lightly to keep coupling speeds safe.
- Trim & depart: In the bowl, cars are coupled into outbound blocks; a trim engine makes up new trains.
Why use a hump?
Gravity does the rolling, enabling high-throughput sorting with fewer locomotive moves.
Gravity does the rolling, enabling high-throughput sorting with fewer locomotive moves.
Typical gradient
~3–6% over the hump with carefully engineered approaches and sightlines.
~3–6% over the hump with carefully engineered approaches and sightlines.
Key hardware
Power points, wheel retarders, speed detectors, cameras, and yard control systems.
Power points, wheel retarders, speed detectors, cameras, and yard control systems.
In 90 seconds
Pictures
Key components
- The hump ("the hill") — A short, engineered rise that provides the potential energy to roll cars into the bowl.
- Crest & cut points — Where cars are uncoupled and released; modern yards use automation and radio control.
- Switches (points) — Remotely set to send cars to the correct classification track.
- Wheel retarders — Rail-mounted brakes that gently squeeze the wheels to keep speeds within safe limits.
- Classification bowl — Many parallel tracks where cars stop, couple, and are later pulled out as new trains.
- Trim lead — The lead used by the trim engine to gather sorted cars and build outbound consists.
Safety & control: Retarder systems are monitored by sensors (axle counters, speed detectors) and yard computers that account for car weight, length, wind, and track occupancy to achieve gentle coupling speeds.
Why hump shunting?
Hump yards maximize throughput for large-scale wagonload freight. By letting gravity do the work, they minimize locomotive movements and operator effort while enabling precise, automated sorting across dozens of tracks. Many of the world’s largest classification yards—such as Bailey Yard (USA) and Maschen (Germany)—use hump systems.
Alternatives
- Flat switching — All moves powered by locomotives on level track; more flexible for small yards but lower throughput.
- Gravity yards (legacy) — Older style using general downhill gradients rather than a compact engineered hump.
Glossary
- Hump
- The small hill a switching locomotive pushes cars over; provides the energy for gravity rolling.
- Retarder
- A track-mounted device that grips wheels to control rolling speed so cars couple safely.
- Cut
- A group of one or more cars handled together during switching.
- Bowl
- The fan of parallel classification tracks where cars are sorted and coupled into new blocks.
- Trim
- The process (and dedicated locomotive) that assembles outbound blocks from the bowl.