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Railway design - Servicing

You're probably familiar with mandatory servicing. It first appeared, I think, on Mike Metcalf's website. But since this trick is most useful, we shall nevertheless discuss some aspects. For those of you who don't know about mandatory servicing: The basic idea behind it is to force the trains into depots regularly and thus to keep the trains' reliability close to the maximum.

In the 'Tracks' sub-section, it is shown that track 'blocks' of the right size (and therefore intelligently placed signals) are a prerequisite for fast train services. But there is one potential cause of traffic jams that we cannot avoid completely and that can happen anywhere, anytime: vehicle breakdown, i.e. breakdown of the locomotive in the case of trains. In order to reduce the number of breakdowns, maintain the following policy:

1. Change the 'vehicle breakdowns' probability from 'normal' to 'reduced' in the difficulty level settings. Well, but frankly, where's the challenge in that?

2. Buy locomotives with high reliabiliy only. In particular, don't buy new versions too early, since they are of low reliability. This usually outweighs higher speed at first.

3. Check your rolling stock regularly. Try to get rid of old locomotives as soon as the reliability of the corresponding class (not just of an individual locomotive) drops below 85 % to 90 %. If the reliability of an individual locomotive of an otherwise reliable class is exceptionally low, take this as a hint that the train can't find its destination anymore or that it has to wait too long for a full load.

4. That last aspect leads to the next point: Keep the trains going! When a train tries to reach a depot that's meant for mandatory servicing, it produces unnecessary traffic. In the worst case, this might even result in traffic jams, because such a train usually takes routes you haven't planned for. To prevent trains from roving around,

   • build easily accessible non-mandatory-servicing depots in the vicinity of stations (e.g. on holdings stacks at stations - see the 'Stations' sub-section) or (and that's better)

   • don't let the trains wait too long for full load by reducing the number of wagons, or trains. Take care in case of industry that produces goods: A large number of goods trains can even block a whole station by preventing other trains from unloading the respective resources.

5. Use mandatory servicing.

Mandatory servicing only works as expected when a particular condition is met. To put it in a nutshell: Trains have to be forced into a depot before they try to go there themselves. You don't need to increase the servicing interval to more than about 150 days, though (that's 5 months!). If a train doesn't get a mandatory servicing within this time, something is definitely wrong with the way you organize train services!

Picture 1 now shows the layout for a standard mandatory servicing depot. The most important feature are the track tiles running past the depot, continuing straight on in the case shown. Without them, trains are prone not to find their destination, because the track leading into the depot and out of the depot doesn't count as continuous. However, a reverse signal must be placed on the track running past the depot, since without it, the train wouldn't care about the depot, but run on without getting serviced. With this layout, the distance trains have to travel is about 40 % longer when compared to the straight section of track. Plus the length of the train! The train is not considered to be inside the depot until its last wagon has disappeared. So, mandatory servicing is beneficial for the reliability of your trains, but don't go to extremes by constructing mandatory servicing depots only a few tiles apart!

Sometimes, there isn't enough space left next to the dual track. So you might want to construct a depot parallel to the track (see picture 2). The distance travelled by trains outside the depot now is 60 % larger, though. So why not shorten the particular section of track the train really uses? The necessary bypass section then has diagonal elements, and the additional distance trains have to travel is really small. Take a look at picture 3 which shows the optimum layout for mandatory servicing. This works perfectly with the dual tracks being one row of tiles apart, as has been proposed in the 'Tracks' sub-section.

Mandatory servicing depots can be placed anywhere along the track. However, they are most useful at the entrance of those stations, where trains have to pick up goods. Before they enter the station, the reliability is reset to the maximum value so that a breakdown during the loading period becomes less likely. On their way to their destinations, trains should encounter just a few depots. Otherwise, they would be slowed down too much and make less money. On their way back though (with the wagons being empty), mandatory servicing isn't much of a time problem. Think about this when connecting stations. Most of the times, however, goods etc. will be transferred in both directions on a dual track, so that about the same density of depots are needed in both directions. Depots also serve as areas of 'retreat', just like track blocks in the vicinity of intersections do. We'll turn to this aspect in the 'Intersections' sub-section.