Transport evidence: who signs a trip generation note

Who signs a trip generation note matters because the number at the end of it drives the whole transport case: whether a transport statement will do instead of a full assessment, how big the junction problem is, and what the highway authority asks for by way of mitigation. There is no statutory licence for this work. In practice the note should be authored by a transport planner or highway engineer with current access to the national trip rate database, experience of the land use in question, and a professional membership that the highway authority recognises.

Nobody checks credentials at validation. The highway authority checks the method, and a note with a weak site selection gets taken apart in the consultation response.

The memberships highway authorities recognise

Transport planning is not a protected title, so the signal comes from chartered status and specialist registration rather than from a statutory register.

A planner with ten years of development work and no chartered status may produce a better note than a newly chartered engineer who has never done one. The letters are a floor, not a ranking. What they give the authority is somebody who is accountable to a professional body if the work is negligent, which matters when a scheme is built out and the junction fails.

Checking the claim takes five minutes. Where the figures carry real weight, a short independent check is money well spent, and our note on peer review of technical evidence sets out when it earns its place.

Database access and what it does to authorship

Most trip generation notes in England draw on the national trip rate database maintained by the TRICS Consortium, which holds surveyed trip rates for a wide range of land uses across the United Kingdom. Access is by subscription, and the subscription sits with a practice rather than an individual.

That has two consequences people miss. A consultant without a subscription cannot produce a database-derived note, so the work will be subcontracted or built from first principles, and a first-principles note is harder to defend. And the person running the query is not necessarily the person exercising the judgement, because the output depends entirely on which surveys were included.

The database also publishes its own good practice guidance on how queries should be constructed and reported. A note that does not show its selection criteria has skipped the part that carries the risk.

Site selection is the whole argument

The arithmetic is trivial. Trip rate multiplied by the development quantum gives arrivals and departures by hour. The defensible part is the set of surveys the rate came from.

A credible note states, and justifies, each of these.

1. The land use category chosen, and why an adjacent category was rejected.
2. The geographic filter, including whether Greater London or Northern Ireland surveys were excluded.
3. The area type filter, so that an edge-of-town survey set is not applied to a town centre site.
4. The date range, with older surveys excluded or justified.
5. The size range of the surveyed sites relative to the proposal, since rates per unit vary with scale.
6. Parking provision at the surveyed sites against the proposal, which drives car driver rates more than almost anything else.
7. Whether multi-modal or vehicle-only surveys were used, and how walking and cycling trips were treated.

Then the adjustments. Internalisation, linked trips, pass-by trade and, on brownfield sites, the existing use's trips being credited against the proposal. Each of those reduces the net figure, each is legitimate in the right circumstances, and each is where an over-optimistic note goes wrong.

The illustrative case I see most often is a retail or leisure scheme where the existing use credit is taken at the lawful use's theoretical full capacity rather than at a realistic level, which can halve the net trip figure on paper and leave the junction modelling built on sand. This example is illustrative.

How the highway authority tests it

The highway authority reads the note against the Planning Practice Guidance on transport assessments and statements, against its own local validation requirements and against whatever thresholds the development plan sets. Its officers have usually seen the same land use assessed on neighbouring sites, so a rate well below the local norm invites a question.

Expect scrutiny of four things: whether the scale of the proposal triggers a transport assessment rather than a shorter transport statement, whether the assessment years and peak hours match local practice, whether committed development has been added to the baseline, and whether the mitigation offered is deliverable within the highway boundary.

Where the strategic road network is affected, National Highways comments separately and applies its own policy on when it will object or ask for a holding direction. On larger residential and mixed-use schemes Active Travel England is a statutory consultee above thresholds set in the procedure order, and its interest is in walking and cycling provision rather than vehicle capacity, so a note that only reports car drivers will draw a comment.

Where a different skill set starts

A trip generation note is a desk exercise. Junction capacity modelling is not, and the two are routinely bundled into one appointment by people who do not realise they are different jobs.

Priority junction and roundabout capacity assessment, signal design and optimisation, microsimulation of a corridor and interrogation of an authority's strategic model all need specific training and, usually, specific software competence. Microsimulation in particular is easy to run and hard to calibrate, and an uncalibrated model is worse than no model because it looks authoritative.

Ask directly who will do the modelling, what calibration data exists, and whether the authority has agreed the scope. Scope agreement before the model is built saves more time than any other single step.

Reviewing a note submitted against you

If you are objecting, or acting for a competing site, the productive attack is on inputs rather than conclusions.

Ask for the full database output, not the summary table. Check the number of surveys behind each rate, because a rate drawn from two surveys carries little weight. Look for a geographic or area-type filter that quietly imports a different kind of location. Test the existing use credit against what was actually operating on the site, with evidence. And check whether the peak hours assessed are the network peaks or the development peaks, since a school or a leisure use peaks when the network does not.

Where the sums matter, commission a short review rather than writing the objection yourself. A technical point made by a transport planner lands differently with a highway officer.

What to put in the brief

Specify the output, the method and the accountability.

Name the deliverable and whether a statement or an assessment is expected. Require the database output to be appended in full, with the selection criteria stated. Require the existing use credit to be evidenced. Ask for the scope to be agreed with the highway authority in writing before the work starts. State who signs the document and under which membership, and confirm that professional indemnity cover is in place at a level proportionate to the scheme. Our guide to the professional directory explains the review route where a draft needs an independent signature.

PlanScope can produce an AI-assisted draft transport statement structured to UK planning policy, with site-specific figures flagged for completion. Councils usually expect a suitably qualified author for transport evidence and professional review is strongly advised, so treat the draft as a starting point for that professional rather than a substitute.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.