Budgeting a transport evidence base by scheme size
The transport evidence base scales in steps. Work out which document the authority requires before commissioning surveys, and order the low cost work so it de-risks the expensive work.
The transport evidence base for a scheme scales in steps, not smoothly. A minor application on an existing access may need nothing more than an access drawing and a short Transport Statement. Cross the local threshold and you are buying junction counts, trip rate data, capacity modelling and a travel plan, and the cost multiplies rather than creeping up. Getting the transport evidence base budget right means working out which step your scheme sits on before you commission anything, because the single biggest cost on most schemes is the survey you paid for twice.
Three variables set the price: the document the authority requires, the number of junctions in the study area, and whether any highway works need designing to a technical approval standard.
Where the statement and assessment thresholds fall
National guidance on transport assessments and statements does not set a single numeric trigger. It asks for the scale of assessment to be proportionate to the likely impact, and it expects the scope to be agreed with the highway authority. The numbers live locally, in the adopted transport and parking standards of the county council, unitary authority or Transport for London.
The thresholds PlanScope uses to flag a Transport Assessment are 50 or more dwellings or 2,500 m² or more of floorspace. Those are useful as a planning assumption, and the authority's own validation list and national policy take precedence over them. Active Travel England becomes a statutory consultee on larger residential schemes, which adds an active travel assessment to the pack.
| Scheme scale | Document usually required | Main cost drivers |
|---|---|---|
| 1 to 9 dwellings, existing access | Access drawing, short Transport Statement | Visibility survey, swept paths |
| 10 to 49 dwellings | Transport Statement with trip generation | Trip rate data, one or two junction counts |
| 50 dwellings or more, or 2,500 m² or more | Transport Assessment | Multi-junction counts, capacity modelling, travel plan |
| Strategic site, new junction | Transport Assessment plus highway design | Model build, road safety input, technical approval |
Agree the scope in writing before you spend. A scoping note sent to the highway officer, setting out the study area, the assessment years, the growth factors and the junctions to be modelled, costs a few hours and saves the rebuild that follows an unagreed scope.
What each document requires in survey data
A Transport Statement is a written case supported by existing data. It needs the site context, the access arrangement, the trip generation, a view on parking and a short set of conclusions. Survey input is usually limited to a visibility check and perhaps a single turning count.
A Transport Assessment is an evidence document. It needs classified turning counts at each junction in the study area, usually over a 12-hour weekday period covering both peaks, queue length surveys where capacity is tight, and sometimes a weekend count for retail or leisure uses. Each additional junction adds survey cost, modelling cost and reporting cost.
Count timing is a hard constraint and it affects programme more than price. Traffic counts should be taken in neutral months, which in practice means avoiding August, December and the school holidays either side of them. A scheme that misses the autumn window waits until the spring.
Trip rate data and modelling costs
Trip generation on most schemes is derived from the TRICS database, which is licensed by subscription. Consultants pass the cost through as a disbursement or absorb it into the fee, and the current subscription rates are published by the database operator rather than fixed in any public schedule, so ask what is included rather than assuming.
Where TRICS holds little data for the use, as happens with specialist employment, last mile logistics and some leisure uses, the trip rates have to be built from operator data or from surveys of comparable sites. Surveying two comparable sites is a real cost and it needs lead time. Flag that risk at the fee proposal stage.
Capacity modelling is priced by junction and by software. Priority junctions and roundabouts are modelled in the standard junction assessment packages, signalised junctions need signal modelling, and anything involving a corridor of linked signals or network reassignment moves into microsimulation, which is a different order of cost and takes weeks rather than days. If the highway authority asks for microsimulation, that single request can exceed the rest of the transport budget combined.
Junction assessment and capacity work
Ask three questions before accepting a modelling scope.
- How many assessment years are required? A base year, an opening year and a future year with committed development is common, and each year multiplies the model runs.
- Are committed developments to be included, and has the authority supplied the list? Chasing a committed development list from a busy highways team is a programme risk.
- Is a sensitivity test expected on growth factors or on the mode share assumptions? Sensitivity tests cost little to run and a lot to retro-fit.
The output that matters to the officer is the ratio of flow to capacity and the mean maximum queue at each arm, with and without the development. Everything else in a capacity chapter is supporting material.
Travel plans and monitoring as recurring costs
A Travel Plan is inexpensive to write and not always inexpensive to run. The document itself is short. The commitments inside it, including travel surveys at stated intervals, a travel plan coordinator, subsidised bus passes, cycle vouchers or a car club space, are obligations that sit with the development for five years or more and are often secured by a section 106 obligation with a monitoring fee attached.
Budget the plan and the delivery separately. A full travel plan with annual monitoring surveys and a remedial measures fund is a revenue line, and on a build-to-rent or employment scheme the operator needs to know about it before the appraisal is signed off. The same logic applies to construction phase obligations, which are set out in more detail in construction management plan conditions and their cost.
Where on-street parking stress is in issue, a Parking Survey to the Lambeth methodology is a defined overnight and weekend exercise. It has to be done in a neutral period, and repeating it because the first survey fell in half term is a wasted cost.
Highway works design and technical approval
This is the cost that surprises people. The Transport Assessment establishes that a junction improvement is needed. Designing that improvement to a standard the highway authority will adopt is a separate commission, and it sits with a highway engineer rather than a transport planner.
A section 278 agreement under the Highways Act 1980 brings in the authority's own fees for checking, supervision and commuted sums, a bond or other security for the works, and often a road safety audit at stages 1 and 2. Those fees are set by each authority and published in its own schedule of charges. Get the current schedule rather than using a figure from a previous scheme, because they change.
Where the strategic road network is affected, National Highways becomes the relevant body and the design standards step up to the Design Manual for Roads and Bridges. That is a longer and more demanding process, and the programme implication is usually larger than the fee implication.
Building a realistic transport budget early
Order the spend so that the low cost work de-risks the expensive work. A scoping note and a visibility check come first. Trip generation and a single junction test come next, because they tell you whether a capacity problem exists at all. Multi-junction modelling, highway design and road safety audit come last, once the layout is settled.
Two habits save money across a portfolio. Keep a register of the survey windows your schemes depend on, so counts are commissioned in October rather than in August. And write the highway authority's published fee schedule into the appraisal as a named line rather than a contingency, because a contingency hides the number from the people making the land bid.
For the narrative documents that sit around the transport evidence, drafting them in-house changes the cost shape. PlanScope prices a single report at £50 and the Professional tier at £150 per month or £600 per year, with unlimited reports and branding removal, which suits a practice producing supporting statements regularly. See PlanScope pricing for the current tiers.
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, and transport modelling and highway design should be carried out by a suitably qualified transport planner or highway engineer.
Frequently asked questions
Is there a national threshold for a Transport Assessment?
No single figure. National guidance asks for assessment proportionate to the likely impact and expects the scope to be agreed with the highway authority. Numeric triggers sit in local transport and parking standards. PlanScope flags a Transport Assessment at 50 or more dwellings or 2,500 square metres, which is a planning assumption rather than a rule.
When should traffic counts be commissioned?
In a neutral month, which in practice means avoiding August, December and the school holiday periods either side. A count taken in a holiday week understates flows and the highway authority will usually reject it. Missing the autumn window typically pushes the survey to the following spring, so commission counts as soon as the study area is agreed.
What does TRICS cost to use?
TRICS is licensed by subscription and the current rates are published by the database operator rather than set in any public schedule. Consultants either pass it through as a disbursement or absorb it in the fee, so ask which applies. Where the database holds little data for your use, trip rates must be built from operator data or surveys of comparable sites.
Why is highway design a separate cost from the Transport Assessment?
The assessment establishes that works are needed. Designing them to a standard the authority will adopt is engineering work under a section 278 agreement, with the authority's own checking and supervision fees, a bond or other security, and often road safety audits at stages 1 and 2. Those fees are published in each authority's schedule of charges.
How much does a travel plan add over time?
The document is short and inexpensive. The commitments inside it are not. Monitoring surveys at stated intervals, a travel plan coordinator, subsidised passes or a car club space can run for five years or more and are often secured through a section 106 obligation with a monitoring fee. Treat delivery as a revenue line in the appraisal.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.