Question

Sketch a ring-barrier diagram for a signalized intersection which shows eastbound and westbound
with permissive lefts concurrent with the through movements (single ring) while northbound and
southbound have leading left protected (2-ring) phasing. Clearly annotate your diagram using
standard NEMA numbering, omit right turn movements, label the rings and the barriers.

Answer 1

Standard NEMA numbering for a 4 legged intersection is as follows

Bue we will not have phase 3 and phase 7, these will go concurrent with 8 and 4. Ignore all pedestrian movements

The ring barrier diagram specifi es the safe sequencing of phases (and thus the movements that they control) at a signalized intersection.

Two standard rules apply for ring barrier settings

1) The phases in a ring must be served sequentially and cannot be served concurrently because they are not compatible with each other.

2) A phase in one ring may be served concurrently with phases in the other ring in the same concurrency group

So for a start seperate the N-S and E-W into two barriers, and then develop from there.

So it will look like this

E-W are in same phase in one single ring, with lefts permitted

N-S both left-turns are leading, after SBL stops, NBT is allowed to start while NBL is still on. Then NBL is stopped and SBT starts

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