Transport Assessment cost: what makes one expensive

A Transport Assessment fee is built from survey work, modelling time and mitigation design, in roughly that order of unpredictability. The writing is a small part of it. Two assessments for schemes of identical size can differ several times over in cost, and the difference is almost always the number of junctions modelled and whether the surveys had to be done twice.

The good news is that most of the expensive elements are set by decisions made before anyone is appointed. Scope well and the fee stays proportionate.

Scoping with the highway authority first

The single largest cost variable is the scope, and the authority sets it. Write before commissioning anything and ask for four things in writing: which junctions should be assessed, which assessment years and growth factors to use, which committed developments to include in background flows, and which trip rate query they will accept.

A scope agreed in writing does two things. It stops an acoustic-style creep where each consultation round adds another junction. And it prevents the most expensive outcome of all, which is a completed assessment the authority declines to accept.

Expect the authority to name junctions you would not have chosen. Argue about them now, at the cost of an email, rather than later at the cost of a model.

Traffic surveys and neutral month constraints

Surveys are the part with a calendar attached. Counts are expected in neutral months, which in practice means avoiding August and the second half of December, school holidays generally, and any period with roadworks or a diversion affecting the junction.

That leaves a limited set of weeks in the year, and it has two cost consequences. Survey companies are busiest in those weeks, and a missed window can push a programme by months, which costs holding charges rather than fees.

Ask the highway authority what count data it already holds before commissioning anything. Authorities often have recent counts on the links in question, and a count taken in a neutral month two years ago is usually more acceptable than a fresh one taken in the wrong week. Where parking is the issue, a dedicated Parking Survey is a separate commission with its own methodology and timing rules.

Trip generation data access

Trip rates normally come from the national trip rate database, which is a subscription service. A consultant with access includes the query in their fee. An applicant without access cannot replicate the work, which is one reason the trip generation section is rarely something to do in-house.

The cost here is in the site selection rather than the extraction. Choosing comparable sites, justifying the filters applied, and defending the resulting rates against an authority that prefers different filters all take time. A query with 40 sites and no stated selection criteria will be challenged, and the rerun is chargeable.

Where the proposed use has thin data, as with specialist leisure or care uses, expect additional work: surveys of comparable operating sites, or an operator's own attendance records converted into a trip profile. That is a genuine extra, not padding.

And watch for mixed-use schemes. Each use needs its own trip rates, its own peak periods and a judgement on internal linked trips between them, which is three pieces of work rather than one. A scheme with housing, a convenience store and a nursery costs more to assess than the same floorspace of housing alone.

Junction capacity modelling

Modelling is priced per junction, and the type of junction matters more than its size.

A priority junction or a roundabout runs in standard capacity software quickly. A set of signals needs signal optimisation work and staging design. A corridor of linked signals, or a junction where queueing from downstream affects the result, pushes the work towards microsimulation, which is a different order of effort and the single most expensive line that appears in these fees.

Three ways to keep this proportionate. Model only junctions where development traffic is a meaningful share of flows, because offering a model of a junction receiving four trips invites questions about the ones you skipped. Agree the software and the validation criteria with the authority at scoping. And settle the access geometry before modelling starts.

Accident data and safety work

Accident records for a five-year period on the relevant links come from the highway authority, sometimes for a fee, and the analysis time depends on how many records exist and whether any cluster needs interpretation.

Where the assessment identifies a pattern, the authority may ask for a road safety review of the proposed access arrangements. That is a separate specialist exercise with its own fee and its own competence requirements, and it is not something PlanScope produces. Budget it separately where an access onto a classified road is proposed.

Mitigation design within the assessment

Where capacity is exceeded, the assessment has to say what fixes it, and that means drawings. Feasibility layouts for a junction improvement, visibility splay plans, swept path analyses for the largest vehicle, and sometimes a preliminary design to support a highway agreement.

This element is open-ended, which is why it should be capped or staged in the appointment. A sensible structure pays for a first mitigation option and prices further options separately, rather than leaving the scope to expand through four iterations.

Pay attention to the order as well. Mitigation designed before the modelling is validated usually gets redrawn, and a drawing produced twice is a drawing charged twice.

Off-site works then bring their own costs outside the assessment fee entirely, including the highway authority's technical approval charges, commuted sums and bonds. Those sit in the appraisal alongside the other infrastructure items described in budgeting utility connections and diversions.

Reruns after a layout change

The most avoidable cost in the whole exercise. A modelled assessment is built on a fixed access position, a fixed internal layout and a fixed unit mix. Change any of those and the trip generation, the distribution and the junction models all need revisiting.

So sequence the work. Fix the access and the quantum, then model. An architect still testing two site layouts should not have a transport consultant modelling either of them.

Two practical safeguards in the appointment. A stated number of model runs included, with a rate for additional runs. And a clear note of what a layout change triggers, so the conversation about cost happens before the work rather than after.

A Transport Assessment is a report councils expect from a suitably qualified author, normally a transport planner, and professional review is strongly advised before submission. A Transport Assessment drafted on PlanScope gives that professional a structured document with the trip generation, capacity and mitigation sections laid out and the survey inputs flagged, rather than a blank page. PlanScope's own pricing is one free report, £50 per report, or £150 a month on the Professional tier, set out on the pricing page. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. For specialist technical reports, qualified professional input may be required.