Signalling in TTD

Signalling for trains in transport tycoon deluxe is a simplified version of what happens in real life. If the section of track ahead of the signal (ie the chunk of track either untill the end of the line or the next signal along) is occupied, the signal is red. If however it is not occupied the signal is green. A train will always stop at a red signal unless you make it ignore the signal. Train depots have their own signals inside them, so a train will wait inside the depot until the section of track outside is cleared.

Directional Signals

One of the new features in the deluxe version of transport tycoon is directional signalling. Trains will always choose a route different from that of a directional signal facing the wrong way. If trains ever run into a signal in the opposite direction they immediately reverse.

As can be seen above trains will always pick a route not involving a signal in the wrong direction to them.

Different properties between directional and normal signals

An interesting property of directional signals (aside from only allowing trains in one direction) is that trains, when choosing a route, pay no attention to whether or not the signal is red. With non-directional signals, the train will ignore a route with a red signal if it can. In the example below you can see the defaul route taken by a train:

Now, even if the train comes across a red signal at the branch, it will still try to follow its default route:

As you can see it sits there waiting at the signal until it finally turns green. Now if you use normal non-directional signals something quite different happens:

The train ignores the red signal and opts to go for the green one. Now why should this happen? Is it a bug? The answer is no. If bi-directional signals did not encourage trains to choose a route without a red signal then it would be pointless to build multitrack stations as trains would not bother to go into an empty platform, they would go to the first track they hit regardless of whether it was taken. So why don't trains pay any attention to red lights on single direction signals? Well if they did things would get pretty hecktic. At junctions especially - For example if a train wishes to branch off onto another track at a junction but the other track's signal is red, then it will choose not to take that track and continue. This would mean chaos with trains constantly getting lost so its a good thing. So remember when building tracks where you want trains to take the route with a green signal build bi-drectional signals.