Path Based Signaling (or PBS for short) is a new feature in OpenTTD that allows you to have more than one train in a signal block. A screenshot of this in action can be seen below, where three trains are sharing a signal block.
All you need to achieve this is to turn on New Pathfinding and to turn off Yet Another Pathfinder for trains, and then build PBS signals at the junctions.If you have a look at this screenshot of the same place slightly later, you have to build special signals to use PBS.
To create these signals, just place normal signals, then press Ctrl and click on them four times, as if placing pre-signals.
Autoplacement of Signals
To prevent players from getting RSI, a feature has been added so you only need to place an entrance and exit PBS signal, and the rest will be automatically converted to PBS signals. To do this, just place normal signals where you want your PBS signals to be, and convert an entrance and exit signal to PBS signals.
The animation below shows you how to do this.
There is one problem with autoplacement. Once you have created the PBS block, you will have to destroy all the signals in order to remove the PBS feature.
Viewing reserved path of trains
The original patches for PBS showed the paths that trains had reserved, and a number of people liked this idea to help with debugging their junctions. The version that was merged into the game still has this option, but it is disabled by default. In order to use it please run the game with the PBS debug level set to 1 or greater. You can do this by passing "-d pbs=1" as a command line option or you can set it via the console with "debug_level pbs=1" (to turn it off change the 1 to a 0).
If you try and modify a live PBS junction it is quite likely that a train crash will occur. As such you should stop all trains before they enter the junction if you need to modify it.
This flavour of Path Based Signaling is not available in OpenTTD stable releases but is available in very old nightlies. If you wish to use PBS use older nightlies (latest version including PBS is r3464). Alternatively, you may download Gonozal's patchpack or the Mini Integrated Nightly (discontinued as of 31 dec 2006) which includes PBS among a number of other patches, or compile your own version using the PBS patch which can also be downloaded from the forums. (Old PBS patch: )