Rail Building
  Part 5: Depots

One of the biggest problems when trying to construct an efficient rail network in TTD is trains breaking down. They cause delays, and depending on the design of your network, can result in traffic jams and other similar problems. One solution to this is simply to turn breakdowns off, which works, but I personally consider this too easy a way out. This page details a few others way you can help mitigate the effects of a breakdown on your network.

Apart from delays, a common problem with trains isn't so much that they break down, but that they will often get lost when looking for a depot. This is particularly the case if you have a junction with limited access to a main line, and a train not intended for that junction goes to a depot off that branch instead of towards its intended destination. The train can then not get back onto the correct piece of track to go where it wants, and in some cases may end up journeying endlessly between a nearby station and the depot, causing inconvenience and delays to the trains that are actually meant to be using this track. The solutions below will help to solve these problems, too.

Force trains into depot

One common solution to this problem is to force trains into a depot as they go about their usual business, like so:

These are the two most common designs. They're both effective and both use about the same amount of space. The trains come from the left/bottom and are forced into the depot because of the one-way signal facing the other direction. Another similar solution is as follows:

The problem with this particular setup, however, is that it can cause problems with the train pathfinder. The train will see that the piece of track is missing and not use that line - it can't see past the depot, as such. On the other hand, the first two solutions work because the pathfinder ignores the direction of signals until the train is within a square or two of it.

Depots in vehicle ordersTTDPatch 1.8.1 alpha 1 introduced the ablility to place depots into a vehicle's orders, using the GoToDepot patch. This feature is also available in recent versions of OpenTTD, with the "Allow goto depot orders" patch. This feature is very useful because, in conjunction with the service interval switch (allowing you to set a service interval of, say, 16,000 days), it eliminates trains (and other vehicles) getting lost when they look for depots - you can now tell the trains exactly where they should go, and when.

On occasions, you may still have issues with two-line tracks (two tracks going in each direction) - if the train is on the inside track and the depot on the outside track, the train is likely to get lost. The design below is asn example of a track setup that allows access to a depot from either track. This design also helps control how many trains are on the inside or outside tracks. By telling the train to go to the inside depot, it will get serviced and be on the inside track.