Website Burkhard Jahnen
 

Railway design - Tracks

What's so special about tracks that they deserve an entire sub-section? Note that we're talking about those sections of railway that lie between intersections or between stations and intersections! Well, both the number of parallel tracks and the distance between individual signals on them determine the maximum rate at which trains enter 'hot spots' like intersections and stations. So, intelligent track design is a powerful tool to prevent these areas from getting overcrowded.

Needless to say, the way computer opponents do track layout is not worth imitating. When you can't afford a dual track at first, don't build it! Let one train earn the money. Let's also keep in mind that

• tracks should run as straight as possible so that their length is kept at a minimum.

• building a track around a high mountain instead of over it is preferable, because the track would otherwise count as a 'slow' connection. Trains are fastest on flat terrain.

• manipulating the countryside at all cost in order to have straight tracks without gradients makes the local authorities very angry. Take a look at the 'Basics' section for a way to reduce this effect.

In the following, we suppose that we can afford dual tracks, each restricting train traffic to one direction by being equipped with one-way signals. What is the best layout then? I propose something like the one shown in picture 1. Note the two characteristics:

1. The tracks are seperated by a row of empty tiles.

2. There are always at least 4 track tiles between two consecutive signals.

The empty tiles in between the tracks can be omitted if there isn't enough space. But they are required in areas of mandatory servicing and in the vicinity of intersections and stations (take a look at the respective sub-sections later on). The reason why that particular distance between signals is chosen is that trains consisting of 1 locomotive and 6 wagons fit in between. This seems to be a reasonable length for a train. That way, tracks are split into several sections or 'blocks'. Just as in real life, trains inside such blocks are protected from potentially interfering traffic by other trains. Inside a block, a train can travel at maximum speed, provided it doesn't experience a breakdown or encounter steep gradients. Since no other train can enter an occupied block, the length of the blocks determines the maximum number of trains on a track. So we draw the following conclusions:

• We want to keep the block length large in order to make trains run fast.

• We want to keep the block length small in order to have a higher number of trains on a track.

From these contradictory necessities it follows that we choose a 'medium' block length of 6 tiles for tracks with low traffic and of 4 tiles for tracks which are used frequently.

So placing a signal on each and every track tile doesn't work!! All you get is a high number of trains as slow as snails. And what's even worse, they get irreversibly stuck really easily!

This statement smoothly leads to one of the most critical issues in railway design: If we can't completely avoid traffic jams (which is true), we should at least provide a track layout that helps resolve it quickly and reliably. In general, really heavy traffic jams occur when two or more trains try to follow crossing routes at the same time. The jams are nearly irreversible, if the trains can't reverse their directions and thus can't leave the area of conflict for a short amount of time. By placing signals on every track tile, trains can't travel back at all. This is the worst possible case. But even with blocks 4 tiles long, we have to be careful in the vicinity of intersections. So blocks should be sections of track where

• complete (!) trains are protected from other train traffic.

• trains can return to by reversing their directions after a period of waiting in traffic jams. Since not all trains involved in a traffic jam will do this at the same time, the 'retreat' of one train most likely opens up the route of another train so that the traffic jam is ended.

Short trains might not be able to retreat into the blocks where they've come from. That's because for this concept to work in the vicinity of intersections, a train should not leave the block entirely, but - when stuck - still have a few wagons inside the block where it has come from. Even a single wagon would suffice. This is the only way for a train to reverse its direction and travel back into a block successfully, since we're dealing with one-way signals here! That's why, for the track layout proposed here, trains should not have less than 5 cars. In the 'Intersecions' sub-section, a track layout will be presented, where these considerations are put into practice.

You might have wondered why I don't say that trains with 7 wagons instead of 6 wagons fit into blocks with the signals 4 track tiles apart. This has to do with the proposed track layout around stations and at intersections: There, blocks usually don't consist of straight pieces of tracks as has been shown in picture 1. When a track is running diagonally  across a tile (see picture 2), then 2 consecutive tiles of the diagonal part count as 1 track tile (Counting like this keeps you on the safe side. Two diagonal track tiles are actually a bit longer than one straight track tile.)! So, in picture 2 we count 3 straight track tiles and "1" additional track tile running diagonally. In fact, a train with 7 wagons would still fit in between. But it would fail to do so if the terminating signal was at the end of the diagonal piece of track rather than on the following straight section. Note the difference by taking a look at the situation shown in picture 3 (For clarification, both signals are shown.). As this latter case is most often necessary in the proposed track layout around stations and at intersections, a maximum number of 6 wagons is recommended. By the way, the way consecutive diagonal tiles are counted as 1 track tile also holds for building entire dual tracks diagonally across tiles. Since this counting can be quite complicated, tracks running straight across tiles are strongly recommended. Don't confuse this with the overall appereance of the tracks: Tracks running diagonally across tiles appear horizontally and vertically on the screen, whereas tracks running straight across tiles actually appear diagonally on the screen!

One final tip on how to arrange dual tracks: Since trains run into dead ends rather easily (so that they can't find their destination anymore), try to construct a mesh of dual tracks. It should consist of two sets of lines perpendicular to each other, just like the streets in Manhattan for instance. The distance between two parallel lines depends on the density of cities, hills and stations, of course. A complete rectangular mesh (i.e. with no pieces of mesh missing) is best in preventing trains from getting lost, though, only when certain rules on where to place stations are followed (more about the actual design in the 'Stations' sub-section):

1. Terminus stations should be constructed close to the dual track mesh. When this cannot seem to be achieved, make the mesh finer by building extra lines. This is recommended for stations on the outskirts of towns. Picture 4 gives an example.
   

   Picture 4

   Terminus stations should be constructed close to the dual track mesh

2. At sites where goods etc. are produced, i.e. at factories in particular, construct through stations (see Picture 5).
    

   Picture 5

   Through stations should lie on the mesh

Large cities thus lie inside the mesh cells (see picture 4, where this mesh is incomplete, though), accessible by several terminus stations. Through stations with heavy train traffic from and to several directions, on the other hand, lie on the mesh itself (see picture 5).

Let me finish this sub-section with some remarks on bridges and tunnels:

• Use the best (and most expensive) bridges: girder bridges and cantilever bridges for normal trains, tubular bridges for monorail connections. Don't slow trains down with inferior bridges.

• For maglevs, don't use bridges at all. All maglev locomotives are faster than the maximum possible speed on bridges.

• Make bridges as short as possible. Since you can't place signals on them, you'd get into trouble with the track block concept. If you have to cross large areas of water, try to 'build' small islands for track tiles with signals.

• The same is true for tunnels: Make short consecutive tunnels, with places for signals in between.

• With bridges crossing other tracks, you can't construct signals or diagonal tracks tiles. That's not the case if you build tunnels instead of bridges.

• By using tunnels instead of normal tracks, you get extra space for planting trees. That looks nice, and the local authorities will like it, too!