By a yard, I will mean any combination of sidings that includes at least one passing siding and one spur siding attached to the passing siding. The simplest type of yard possible is shown in the diagram below.
This yard allows the spur siding to be switched by trains going in each direction. If a train is going from right to left, then the turnout for the spur siding presents a facing point for the train. To see how to switch facing points, go to the article on TRAINING. When a train going from right to left switches the spur siding, it will have to block the mainline as the locomotive runs around the train to switch from behind. It may also have to leave a car on the mainline for a short time during the switching maneuver. A train going from left to right will have to leave all the cars behind the car it is setting off on the mainline as well. So any train switching the spur siding will "foul" the main. This will prevent other trains from passing and cause congestion.
Now look at the redesigned yard below.
This configuration uses more space and requires more track, but it has the same number of switches. Now trains moving in each direction can switch the spur siding without leaving any cars on the mainline. The only time the mainline is blocked during a switching operation is when the locomotive of a train moving from right to left runs around the train to switch the facing points. Designing your simple yards so the turnout for any spur sidings are in the middle of the passing siding with room on either side of the turnout to park cars will reduce traffic congestion and improve operations.
You may have seen various switching problems in model railroad magazines. These are fun as puzzles, but you don't want one in your layout if you plan to have operating sessions. Trust me on this. When I first designed our main yard at Rivendell, I included such a puzzle. The result was that all our trains ended up at this yard because it took so long to switch the industries. Real railroads only put sidings in places that are difficult to switch because the space limitations of the vicinity leave them no choice. Time is money. Real railroads will design yards to make switching as easy as possible. I tore the entire Rivendell yard out and redesigned it - twice - before I got something that works smoothly. The result is the diagram below.
The Rivendell Yard
If you look at the Lake Town & Shire track plan, you will see that this yard is actually built on a curve, but I have straightened it out here for simplicity. The mainline is at the bottom of the diagram. Track EF goes off to the engine facility which includes a coaling station, a water tower, a turntable, and a roundhouse. R1 and R2 are receiving tracks. Trains needing to switch cars at this yard pull onto R1 or R2. R2 also serves as the "drill track" for switching the interchange and industry tracks. A train coming from the left runs onto R1 and drops any cars that go on to other destinations. Then the locomotive and the remaining cars can pull onto R2 to set out and pick up cars on the interchange and industry tracks. Trains coming from the right pull onto R2. The train is uncoupled in front of the first car to be set out on one of the interchange or industry tracks. The front of the train then runs onto R1 and backs out onto the mainline until it can pull back onto R2 from the left. Then the train can set out and pick up cars on the interchange and industry tracks. When finished, the locomotive and any cars behind it run back around the train on the mainline to get back in front of the train. R1 and R2 are long enough that a train can wait on either track while a train that arrived on the other track finishes switching. (Remember that the maximum train length on the Lake Town & Shire is a locomotive and tender, three cars, and a caboose.) So one train can be switching the yard, another train can be waiting on one of the receiving tracks, and the mainline is clear for any other trains to pass through.
Two final lessons I have learned is that you all switches to be easily accessible, preferably without walking into the layout, and you want to use only as many switches as you absolutely need. The Rivendell yard above is at ground level and there is a path directly in front of the mainline. The yard is so wide that operators must walk into the yard to uncouple cars, but there is plenty of room between R1 and the interchange and industry tracks where operators can stand. And the only buildings on this part of the layout are beyond the interchange and industry tracks. I tried putting a temporary depot in this space, but one of my operators wiped it out. I also had a logging spur on a section of track where operators had to walk across a dry stream bed to switch the spur. We quickly realized that children could turn an ankle or fall down trying to cross the dry stream bed. So I took this siding out and we now have a nice, long stretch of mainline in this area.
Old Hobbiton Reverse Loop and Yard
These last two lessons also apply to the design of the smaller yard at Hobbiton. You can see the original design in the diagram above. This area of the layout is raised about two feet above ground level with a wall all around. Notice that there is a reverse loop, a passing siding built into the reverse loop, and three industrial sidings coming off the loop. The right hand turnout at the top of the diagram was spring loaded so that trains entering the loop went to the left into the yard. You could allow a train to pass on the passing siding, but to do this an operator would have to walk all the way around this raised section of track to change the switches at the top of the diagram. Also, operators had to climb onto the raised section and maneuver between the buildings to switch the industrial sidings. All in all, this was not a good arrangement.
Almost every train that comes to Hobbiton will do some switching. So we really didn't need the passing siding. If there is a train already switching this yard, an incoming train can wait on the mainline to the left until the first train has finished switching. After switching, the first train can go into the curve of the loop to wait for the incoming train to enter the yard. Then the first train can leave Hobbiton. I took out the passing siding. I also rearranged the industrial sidings so that all the turnouts could be reached and all the cars could be uncoupled from the front of the layout. The result was the design below.
Reverse Loop and Yard