Mandatory Servicing

10.1Standard mandatory servicing10.2Mandatory servicing with two squares width
10.3Mandatory servicing with the minimum trains way10.4Mandatory servicing with two depots
10.5Standard mandatory servicing used with traffic route in both the directions10.6Mandatory servicing with two depots used with traffic route in both the directions
10.7Mandatory servicing with two depots used with traffic route in both the directions. Alternative  
"In the race to make millions, vehicle breakdowns are probably your biggest obstacle. In a busy station serving a dozen trains or more, having even one train break down on its way into or out of the station can cause freight-train gridlock. Other trains waiting to get in or get out will also break down, causing a chain reaction of breakdowns which cause ratings to nosedive and profits to plummet." (c) Mike Metcalf
Mike is absolutely right, that's why I gathered mandatory servicing schemas from the different places and designed some more. Schemas for a single route direction are represented first.
Let's see what Burkhard Jahnen in his «Railway design - Servicing» section say (my comments are placed in brackets):
Schema 10.1
Schema 10.2
"Schema 10.1 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. (A train from A turns on the signal C and through signal E goes in the depot D and than through signal F goes to B) 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!
Schema 10.3
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 schema 10.2). 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 schema 10.3 which shows the optimum layout for mandatory servicing."
Schema 10.4
And now, let's have a look at the combined depots. A dual depot schema (schema 10.4) is designed by Chris Doherty. That is what he says about it (my comments are placed in brackets): "A very useful application of this arrangement is in implementing a "dual depot" (or more if you want) that gets trains in and out alot quicker than one depot on it's own. Observe: You can see that a train reaching the fork (A) will see the "two-way" signals (E and E') in front of it and choose the track that is free. This allows a train to enter one depot while another train is either leaving the other depot, or still going into it (e.g. to choose D' if D is in use). This setup is very useful for high traffic lines."
Schema 10.5
But what can be done if the line works in both the directions?
The simple and reliable solution is just to put the standard schemas, used in the traffic route with specified direction (schema 10.5), without direction signals A and B.
Schema 10.6
And what can be build using combined depots in case of traffic route in both the directions? Schemas 10.6 and 10.7 provide a solution, which gives the train, moving in any direction, two possible depots for servicing plus additional buffers G and G' after the depot in case of schema 10.6 and before the depot in case of schema 10.7 This schema also requires the pre-signals for functioning, because without pre-signals trains from opposite directions can lock ore reverse each other before depots at signals C' and C''.
Schema 10.7
A buffer G/G' before the depot blocks a way to depot in case the train, coming from the depot, waits a free way, but reduces the servicing intervals. A buffer G/G' after the depot does not block a way to depot in case the train, coming from the depot, waits a free way, but a train in buffer waits a way after servicing, that increases the servicing intervals.
But the capacity of such a schema is much higher, than the capacity of a one-line way, that means, a time wasting practically absents.
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