Junction modelling and capacity assessment.
Junction capacity modelling with Junctions (ARCADY and PICADY) and LinSig, calibrated properly and explained in plain English.
Also known as: junction modelling, junction capacity, capacity assessment, Junctions software, Junctions 10, Junctions 11
What’s included.
Where a scheme adds traffic to a busy junction, the council may ask for capacity modelling. The result helps answer whether any effect is severe under NPPF policy TR6(4), and what mitigation, if any, is justified.
- Junctions (ARCADY and PICADY) models
- LinSig signal models
- Base model validation against queue surveys
- Future year with and without the scheme
- Mitigation testing
- Clear summary tables and plain-English findings
Straightforward, proportionate, agreed early.
Only where needed
We model the junctions the scheme genuinely affects.
Validated
Base models checked against observed queues, so officers trust the results.
Explained
What the numbers mean for the severe test, in plain English.
Questions we get asked
What do RFC and degree of saturation mean?
Ratio of flow to capacity (RFC) is used for roundabouts and priority junctions, and degree of saturation for signals. Values near or above 0.85 or 90% suggest a junction is approaching capacity.
Does a junction over capacity mean refusal?
No. The test is whether the residual cumulative effect is severe, which is a judgement, not a single number.
Which software do you use?
Junctions (ARCADY and PICADY) from TRL, and LinSig from JCT.
Often needed alongside.
When modelling is needed, and when it is not
Junction modelling is needed when a scheme adds a meaningful amount of traffic to a junction that is already busy. For many smaller schemes, the extra trips are too few to change how a junction works, and a short explanation is enough.
Where modelling is needed, we agree the junctions, the scenarios and the inputs with the highway authority first, so the results answer the question the officer is asking.
- Base model checked against observed queues.
- Future year tested with and without the development.
- Mitigation tested only where the results show it is needed.
Last reviewed October 2026 by Ripple Development Planning. Policy and guidance change; for advice on a specific site, send us the details.
From our insights.
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