In several GRFs it happens that several locs are limited to a certain kind of cargo, and that the fastest trains are pax-only. So if we wanted to have those trains coexist on the same network, then we should make sure the fast trains can follow their way without experiencing much hindrance from other trains.

To obtain that, a mainline would be at least 2 wide in one direction, and lane to the left would be reserved for faster traffic. Since speed can not be measured absolutely, a system like this would only work when there is a difference in speed. Trains will therefore use one track while unhindred, and only when encountering a slower train will they decide to switch lanes.

Prototypes have been built, images and savegames coming