Changes

* ''At the switch'' where train can choose '''any''' tracks and should wait for '''the first available''', if all of the tracks are occupied. Most common use is at multi-platform stations (assuming all platforms are equal, i.e. every track leads on to every possible destination), at parallel tunnels (signals cannot be placed inside the tunnel, so longer tunnel becomes a bottleneck for the rail network. That could be mitigated by building parallel tunnel in the same direction, which doubles the number of trains traveling at once) or at any other parallel tracks built to increase the throughput of the network. Take this three-track station below. Imagine all three tracks being occupied and a fourth train arriving. Without the chain signal, the fourth train would choose one station track, and enter it stopping until the train '''of that track''' leaves the station. Even if both the other two trains leaves the station first, this fourth train has already chosen its track, and will wait until that track becomes available. While it does so, it blocks the junction and therefore all traffic. With a chain signal instead, the train will stop ''before'' the junction, and once ''any'' track becomes available, the train will choose that track. This is obviously more efficient and removes a common source of blocked stations.