Traffic distribution and assignment.
Traffic distribution based on Census journey-to-work data and local evidence, so trips go where they really will, not where it is convenient to assume.
Also known as: traffic distribution, trip distribution, traffic assignment, journey to work data, gravity model
What’s included.
Distribution decides which junctions a scheme affects and by how much. Officers scrutinise it closely. Census journey-to-work data, survey turning proportions and gravity models are the usual methods.
- Census journey-to-work analysis
- Survey-based turning proportions
- Gravity models for retail and leisure
- Route assignment
- Study area definition
- Clear diagrams and tables
Straightforward, proportionate, agreed early.
Evidence-based
Real travel patterns from the Census and surveys.
Proportionate
A method matched to the scheme, from simple splits to full gravity models.
Visible
Diagrams that show exactly where trips go.
Questions we get asked
Is 2021 Census data reliable for journeys to work?
It was collected during the pandemic, so many practitioners still use 2011 data or compare the two. We agree the approach with the council.
Can distribution reduce the number of junctions to assess?
A robust distribution shows where traffic genuinely goes, which often confirms some junctions are barely affected.
Do you use gravity models?
Yes, where they suit the use, such as retail and leisure.
Often needed alongside.
Where the new trips will go
Once trip numbers are known, they have to be assigned to the road network. The choice of method changes which junctions see the traffic, so it is often the first thing officers check.
- Census travel-to-work data for the local area, used with care because the 2021 Census was taken during lockdown.
- Turning proportions from traffic counts at nearby junctions.
- Gravity models, weighting destinations by size and distance, for larger or mixed-use schemes.
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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