Transport statement or transport assessment: the thresholds

Whether you need a transport statement or transport assessment is decided by the local highway authority, not by a national figure, and the honest answer for most schemes is that you ask before you draw. National guidance sets no numerical threshold at all. It asks for the work to be proportionate to the scale of the development and the extent of its transport impacts, which leaves the numbers to validation lists, highway authority guidance and the scoping conversation.

That is unsatisfying if you are pricing a job. So here is the practical position: below roughly 50 dwellings or 2,500 m² of floorspace, most authorities in England will accept a transport statement. Above it, expect to be asked for a full assessment. Those are the figures PlanScope uses to flag the heavier document, and they reflect common practice rather than any statutory rule. Your authority's published validation list takes precedence over both.

What separates the two documents

A Transport Statement is a proportionate description. It sets out the site and its existing access, the highway conditions around it, the accessibility of the site by walking, cycling and public transport, an estimate of the trips the development will generate, the parking and servicing arrangements, and a short assessment of whether any of that is unacceptable. Twenty to thirty pages, no traffic modelling, no junction capacity work unless something specific demands it.

A Transport Assessment is an evidence base. On top of everything in a statement it will normally contain traffic surveys, trip generation derived from a national survey database with the site selection set out, trip distribution and assignment across the network, junction capacity modelling in an agreed opening year and a future year, personal injury collision data for the most recent five years, an assessment of the effect on the strategic road network where relevant, and a mitigation package. It runs to a main document plus appendices that are usually longer than the report.

The difference in fee is substantial, which is why the scoping stage repays the time it takes.

The thresholds authorities actually apply

Most highway authorities publish indicative thresholds in a local validation list or in their own transport guidance. The pattern is consistent enough to plan around, though the figures vary.

Three things override the table. A site in a congested or accident sensitive location can attract a full assessment at a fraction of those numbers. A site whose access needs alteration will be judged on the access, regardless of scale. And a scheme of 150 or more dwellings brings Active Travel England in as a statutory consultee, with alternative floorspace and site area triggers, so check the current consultation arrangements for anything approaching that size.

Scoping it with the highway officer

Write to the highway authority before you commission anything. A scoping note of two or three pages is enough, and it should ask for agreement on a specific list:

1. The document required, statement or assessment.
2. The trip generation source and the site selection criteria you propose to use.
3. The assessment years, normally the opening year and a future year, and the growth factors applied.
4. The committed developments to be included in the future case.
5. The junctions to be modelled, if any, and the software.
6. The survey dates and whether existing counts are acceptable.
7. Whether a travel plan is needed, and at what level.

Get the reply in writing and put it in the appendices. Half the objections that arrive at consultation stage are about scope rather than substance, and an agreed scoping note removes them. Where the strategic road network is in play, the position is different again and National Highways applies its own policy, which we cover in the note on strategic road network access under Circular 01/2022.

Trip generation and how much analysis follows from it

The scale of the analysis follows from the number of trips, so the trip rate decides the cost of the work. That is why highway officers scrutinise the site selection behind a rate more closely than the rate itself, a point covered in detail in our note on transport assessment thresholds and trip generation.

For a statement, a simple comparison of trip rates from comparable surveyed sites is usually enough, with the peak hour figures stated for the morning and evening periods and a sentence on what those trips mean for the nearest junction. For an assessment, the same rates are distributed across the network using census journey to work data or a local model, and the resulting flows are tested at each agreed junction.

An honest note on precision. Trip rate work looks exact and is not. Two defensible site selections can produce rates that differ by a third, which is why sensitivity testing matters more than arguing about the central figure.

Change of use, and the value of netting off

For a change of use the question is the net change in trips, not the gross. An existing lawful use that generates 40 two-way trips in the evening peak is a fallback, and the assessment should compare the proposal against that rather than against an empty building.

Two cautions. The fallback has to be a lawful use that could realistically start up again, so a unit vacant for eight years with no prospect of reoccupation is a weaker argument than one trading last month. And the profile matters as much as the total: a shop that generated trips through the day and a gym that concentrates them into the evening peak can have the same daily total and very different effects on a junction.

Where the change of use falls within class E, the permitted movements inside that class also form part of the fallback picture, and it is worth setting that out explicitly rather than leaving the officer to work it out.

Travel plans and where they attach

A travel plan is a separate document with a separate purpose, and it usually accompanies the larger schemes. A framework plan is acceptable where the end occupier is unknown, with a full plan secured by condition or obligation before occupation. For schemes with a known occupier, a full Travel Plan with baseline surveys, mode share targets, a named coordinator and monitoring intervals is expected from the start.

Do not fold the travel plan into the transport assessment as a chapter. Authorities secure travel plans through obligations and need them as standalone documents that can be monitored and updated.

Illustrative example: a 38 unit scheme on a brownfield site with an existing vehicular access. The authority's validation list asks for a transport statement above ten dwellings. The scoping reply confirms a statement, no junction modelling, trip rates from a residential land use category filtered to edge of town sites surveyed in the last ten years, and a framework travel plan secured by condition. The transport work comes in at a fraction of the assessment fee and nothing is queried at consultation. Illustrative only.

The pattern to take away is simple enough. Ask first, agree the scope in writing, and let the agreed scope define the document rather than guessing at a threshold and hoping.

This is general guidance rather than 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. Enter your postcode on PlanScope to see which transport documents a site is likely to need.