Rail yard

Many yards are located at strategic points on a main line. Mainline yards are often composed of an up yard and a down yard, linked to the associated direction of travel. There are different types of yards, and different parts within a yard, depending on how they are built.

Freight yards

For freight cars, the overall yard layout is typically designed around a principal switching (US term) or shunting (UK) technique:

• A flat yard has no hump and relies on locomotives for all car movements.
• A gravity yard is built on a natural slope and relies less on locomotives; generally, locomotives will control a consist being sorted from uphill of the cars about to be sorted. They are decoupled and allowed to accelerate into the classification equipment lower down.
• A hump yard has a constructed hill, over which yard locomotives shove freight cars, and then are propelled by gravity to various sorting tracks.

Sorting yard basics

In the case of all classification or sorting yards, human intelligence plays a primary role in setting a strategy for the switching operations; the fewer times coupling operations need to be made, and the less distance traveled, the faster the operation, the better the strategy, and the sooner the newly configured consist can be joined to its outbound train.

• Switching yards, staging yards, or shunting yards are typically graded to be flat yards, where switch engines manually shuffle and maneuver cars from (a) train arrival tracks, to (b) a consist breakdown track, to (c) a consist assembly track, thence to (d) departure tracks of the yard.
  • A large subgroup of such yards is known as staging yards, which serve as end destinations and collection yards, starting car groups for departure. These seemingly incompatible tasks arise because the operating or road company and its locomotive drop off empties and pick up full cars waiting for departure, which have been spotted and assembled by local switch engines. The long-haul carrier makes the round trip with minimal turnaround time, and the local switch engine transfers empties to the loading yard when the industry's output is ready for shipment.
  • This activity is duplicated in a transfer yard, the difference being that in the latter, several industrial customers are serviced by the local switcher, which is part of the yard equipment, and the industry pays a cargo transfer fee to the railroad or yard operating company. In the staging yard, the locomotive is most likely operated by industry personnel (refinery, chemical company, or coal mine), and, in both cases, ownership of the yard is a matter of business and could be any imaginable combination. Ownership and operation are quite often a matter of leases and interests.

• Hump yards and gravity yards are usually highly automated and designed for the efficient breakdown, sorting, and recombining of freight into consists, so they are equipped with mechanical retarders (external brakes) and scales that a computer or operator uses along with knowledge of the gradient of the hump to calculate and control the speed of the cars as they roll downhill to their destination tracks. These modern sorting and classification systems are sophisticated enough to allow a first car to roll to a stop near the end of its classification track, and, by slowing the speed of subsequent cars down the hump, shorten the distance for the following series of cars so they can bump and couple gently, without damaging one another. Since overall throughput speed matters, many have small pneumatic, hydraulic, or spring-driven braking retarders (below, right) to adjust and slow speed both before and after yard switch points. Along with car and load tracking to the destination, technologies such as RFID enable long trains to be broken down and reconfigured at transfer yards or in operations in a remarkably short time.