Priority Merge

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Railway Junctions
Junction Criteria

3-Way junctions

Basic 3-Way
Line Merge
Half Cloverleaf
Half Spaghetti
Compact 3-Way
Compact 3-Way B-M Junction
Ultimate 3-way
Half Transmogrified
Braided Junction

4-Way junctions

Basic 4-Way
Complex Star
High Speed 4-Way Fly-over/under
Pre-Signaled Roundabout
Advanced Roundabout
Right-of-way Roundabout
Improved Roundabout
Deepblue2k8 4-way Junction

Enormous junctions

Multi-way/multi-track cloverleaves
Dual Tetrathorp
Dual Transmogrified
Dual Branch-Merge
Quad Branch-Merge
Quad Tetrathorp
6-tuple Branch-Merge
8-Way Star
High Speed 4-way

Other junctions

Right-of-way Depot
Dual tunnels
Sideline U Turn
Right-of-way Lane Change
Right-of-way Merge

Track Layouts

4-Way Triple Axial
4-Way Triple Axial 2
Triple Via Mini
High Hill

Unuseful junctions

3/4ths junction
Ultimate 3-way junction for 4 tracks

All merging is bad, especially if either line is very busy. When trains start queueing they merge alternately. This sounds like a great idea, but because the trains are starting from stationary each time it's very slow. Your network will be better off giving priority to one line and allowing it to clear at full speed before the other line can merge. This is especially useful for joining a main line.

Using pre-signals in a simplified version of the Right-of-way Lane Change and Right-of-way Depot you can force trains joining your mainline to wait for a gap. With a dual mainline this works even better, as you can let trains on the inside move to the outside to let trains join.

Basic Priority

The simplest form of priority.

With two-way pre-signals and nothing extra you can force a merging train to stop if there's a train already on the main track directly in front of the combo or exit signal. The disadvantage to this construction is you can't extend the priority further than the length of two signals.

Priority Merges Using Extra Track

Priority merges using different signal types.

Longer priority can be designated by connecting track to activate the main merging signal upstream. When a train on the prioritized track drives onto a tile connected to the unused track it tells the signal on the merging track to read red. This construction can be made with both path signals and regular block signals on your tracks. The path signal construction needs only a single block signal on the merging track, while the block signal construction requires pre-signalling on the unused track to prevent trains from signalling themselves to stop.

Be careful to construct priority merges to accommodate your shortest train's length. If you have too much space in the middle, a train can briefly occupy a section of track without activating the merge signal, allowing a train to merge and disrupt traffic. This can be prevented by splitting longer priority into segments.

A flawed priority merge with too much un-prioritized space. Notice the merging signal is green when a train on the main track is in the very center.
Longer priority merge fixed by splitting the priority into segments. The merging signal will read red no matter where a train is on the priority

Right-of-way Merging onto Dual Mainline

One method of merging onto dual mainline without disrupting traffic.

All signals are combo signals except at points A and B which are entry signals, and the top right, which are exit signals. Adjust the length of the signal chain according to train length and speed.

Trains joining at point A must wait for the presignal chain along the inside lane to be clear. If a train arrives at point B before train A is out of the way then it will switch to the outer lane (at no speed penalty), but only if the presignal chain for the outside lane is clear. If it is not, the presignals at point B ensure that train B will take the line which clears first.

The vertical section of track at point C is optional. It allows A to continue if the presignal chain for the outside lane is clear, even if the inside lane is not, as the train on the inside will move to the outside to let A out. Without it, A will always wait for the inside lane to clear, regardless of the state of the outside lane.

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