Right-of-way Lane Change

From OpenTTD

Railway junctions 3-Way junctions Basic 3-Way Line Merge Half Cloverleaf Half Spaghetti Compact 3-Way Compact 3-Way B-M Junction Ultimate 3-way 4-Way junctions Basic 4-Way Roundabout Cloverleaf Spaghetti Star Complex Star Branch-Merge Over-Under Tetrathorp Pre-Signaled Roundabout Advanced Roundabout Right-of-way Roundabout Enormous junctions Double Cloverleaf Dual Tetrathorp Dual Branch-Merge Quad Branch-Merge 8-Way Star Other junctions Right-of-way Depot Dual tunnels Right-of-way Lane Change Unuseful juctions Crossover 3/4ths junction Ultimate 3-way junction for 4 tracks

For multi-lane networks with lots of traffic, sometimes you may want to let trains switch lanes. If one lane backs up, trains can switch to another free lane. However, the lane-switching train might cause a traffic jam behind it in the new lane! With pre-signals, you can make trains wait for an opening in the 2nd lane before merging.

In the above picture, train A is stopped due to a jam further ahead. Train B decides to go around it by switching lanes. Train C comes and makes B have to wait to merge. This allows B to not wait in the jam, but also not cause a jam in the 2nd lane.

This junction is very useful before large railway stations.