There are two types of Gravity freight yards, "Hump Yards", and "Downhill Yards". In a humpyard the train to be sorted is pushed up and over a large hill called the Hump and the cars are allowed to roll into a sorting fan of tracks. In a Downhill Yard the yard is built on terrain with a natural slope with the receiving yard above the sorting and departure yard. A fixed retarder or very small hump is used to put slack into the train so that the pin can be pulled and separation between cuts of cars can be achieved. With a Downhill Yard lots of braking power is required and it is common to see brake sleds used, as lots of tractive effort isn't required. Two major Downhill Yards exist, West Colton Yard (ex- SP) on the Union Pacific. And Cherokee Yard (ex- SLSF) on the BNSF. Smaller versions without retarders also exist. West Colton Yard used slug sets rather than brake sleds as due to layout it is required to haul the departure cuts back uphill, but the slug sets featured extended range dynamic braking to control speed when holding back heavy cuts on the downhill lead track. There used to be many more Downhill yards where brakemen would ride the car and apply the hand brakes. Rather than Kicking the cars the cut was allowed to roll and a sudden application of the engine brakes had the same effect as a "Kick". This is where a Brake Sled came in handy, as a supplement to the brakes on a locomotive.
