Railroad Operations – The Yard

25 04 2012

Railroad yards come in all shapes and sizes and they perform a variety of functions. Most yards do more than just store trains. Yards are dynamic places where trains are taken apart, rearranged and put back together. Locomotives and cars may be fueled, cleaned and repaired. In some yards, there are tracks for loading and unloading trains as well. Over the coming weeks we’ll look at several different types of yards, their functions, and how you can add them to your layout. We’ll begin with one of the most common and complex types of yards – the Classification Yard.

The Classification Yard

arrival yard

The yard process begins at the arrival yard. The tracks to the left and rear of the approaching CSX coal train hold incoming trains that will be switched. Unit trains like this coal drag don't require a stop in the yard.

When you think of a rail yard, this is probably what comes to mind. A sprawling facility with dozens if not hundreds of tracks – each of which has a purpose. At the ends of the yard, switching locomotives move back and forth with cuts, or strings, of cars – shuffling from one track to another as the big freight trains roll in and out from the mainline. These yards are the key to railroad operations.

The railroad functions very much like a postal service, with local trains picking up and delivering parcels (cars) at customers’ sidings. The cars that are picked up are destined for points all across the country, so they must be sorted and grouped by their destination. The classification yard is like the post office, where all of this sorting takes place and the cars are placed into proper outbound trains. These trains may take the car directly to the next customer, but more than likely they’ll pass through at least one or two more yards along the way. Local yards feed bigger yards – or hubs – which can funnel traffic in volume across great distances.

Sorting the Cars

Freight doesn’t make any money or get any closer to its destination in a yard, so minimizing a car’s time here is important. Railroads use two different methods of sorting cars. Traditional, or “flat” switching uses a locomotive and crew to place cars on proper tracks according to destination. The crew must work back and forth through the array of switches, called a “ladder,” to spot each car.

Hump Yard

Cars roll over one of two humps at Union Pacific's Bailey Yard in North Platte, Nebraska - the largest freight yard in the world. This hump handles westbound traffic. A pair of covered hoppers have just passed the crest and are rolling into the bowl.

Another method uses gravity to help speed the process. In a “hump yard” the switching locomotive pushes cars to the top of a small hill. At the crest, the cars are uncoupled and roll through the switch ladder on the downhill grade into the bowl of classification tracks. In both hump and conventional yards, there is often a small grade near each end of the yard to prevent cars from rolling out of the bowl and back into the switching ladder, yard leads or mainlines.

Since cars being switched down a hump must have their air brakes bled off, their speed must be controlled by other devices to prevent rolling too far, or crashing into other cars too hard. In earlier years, brakemen would ride the cars into the bowl, controlling speed with the handbrake. After riding the car down, they would walk back to the hump. Some railroads had dedicated return tracks in the hump with speeders to return the brakemen faster and with less interference from oncoming cars. The hump bowl is one of the most dangerous places on the railroad as you often can’t see or hear what’s coming at you.

hump power

Railroads need strong power capable of maintaining an even slow speed for pushing cars over the hump. This SD38 and "slug" combination at work in BNSF's Argentine, Kansas yard is typical of modern hump switchers. The slug does not have a diesel engine of its own, but draws power from the mother unit.

Since the 1930s, railroads have installed air-powered “retarders” which apply friction to the flanges of the wheels as they roll down the hump to slow the car. Railroads employed early computers in the hump that could calculate the weight of the car (via a scale at the crest), its speed and the distance required to a coupling with the next car in the track to calculate the speed needed leaving the hump and set retarder pressure accordingly. Today’s computers also account for such variables as wind speed and rain.

With all of this technology, damage from excessive speed in a hump yard is minimal today, but you’ll still often see cars with odd, hazardous or fragile loads placarded as “DO NOT HUMP” which means they should not be switched in such a manner, and should be handled with care in conventional switching as well.

Building Trains

As incoming trains are broken apart and sorted, outbound trains must be put together. Depending on the amount of traffic and the size of the yard, an entire classification track may become a single train. Often, several tracks of shorter cuts of cars are strung together. These pre-sorted blocks of cars may be set off at different yards along the way, or simplify switching at the next yard down the line.


A pair of yard switchers pull long cuts of cars from the classification tracks on parallel switching leads in Argentine Yard. To the right, an outbound train is starting out of the departure yard. Just beyond, a smaller local yard handles make-up work for cars bound for nearby customers.

With the cars in line, air hoses are connected, an inspection made, and a caboose and locomotives added. This may be done directly from the classification part of the yard, or more frequently, in a separate area or “departure yard.” Like the arrival tracks, these yard tracks are long enough to hold the complete train and allow crews to make inspections and do their work without the constant threat of other cars drifting about.

Now that you’ve got the basics of what really goes on in a classification yard, next week we’ll look at some of the other operations that are commonly found within before we talk about how you can make it all come to life on your model railroad.



5 responses

25 04 2012
Doug Neumann

I enjoy reading these posts, thanks.


25 04 2012
Peter L

As a guy that grew up playing with and watching trains I stumbled on your blog. I forwarded it to my son and we are now discussing trains and your blog posts. Thanks for the “re-education” for me and the opportunity to share with my son.

25 04 2012

Great post I enjoy reading it.

25 04 2012

I look forward to these emails, this was a good one..I am setting up my layout now, I need all the help I can get.

27 04 2012
Andrew Falconer

Automobile Carriers have the DO NOT HUMP decals on them. To avoid the need for sorting at most yard Auto Carriers are often in unit trains.

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