Traffic counts in neutral months and why August fails
Neutral month traffic counts are the baseline highway authorities accept. Which months and days work, what weather and roadworks do to a survey, and how far ahead to commission.
A traffic count taken in neutral months is the only baseline a highway authority will accept without an argument, and August is not one of them. Schools are closed, a large share of the working population is away, and flows on most suburban and urban links fall well below the term-time norm. Submit an August count as your baseline and the highway officer will either reject it or apply a correction factor of their choosing, which is worse, because you have lost control of the number.
Neutral months are a convention rather than a statutory rule. They are applied consistently enough across English highway authorities that treating them as a rule will save you a survey.
What a neutral month means
A neutral month is one in which observed traffic is representative of typical conditions: schools in term, no extended holiday period, no seasonal distortion from tourism or agriculture, and no systematic weather effect.
In practice the months usually accepted are March, April, May, June, September, October and November. Even within those, weeks containing a bank holiday or a school half term are excluded, and the week either side of one is treated with suspicion.
Tuesday, Wednesday and Thursday are the neutral days. Monday and Friday carry different travel patterns, with Friday afternoons in particular showing a spread peak that flatters a junction assessment.
The months normally excluded
| Period | Why it is excluded |
|---|---|
| January | Post-Christmas depression in flows, weather disruption |
| February half term week | School term effect absent |
| July, late in the month | Schools break up, flows fall |
| August | Main holiday period, flows well below typical |
| December | Christmas retail distortion and holiday period |
| Easter and the surrounding weeks | Variable date, school holiday |
The exclusions are not symmetrical. December is unusable for a residential site because flows are depressed, and unusable for a retail or town centre site for the opposite reason, because they are inflated. Say which effect applies to your site when you agree the dates.
There are sites where the convention inverts. A count for a coastal caravan park, a farm shop or a visitor attraction has to capture the peak season, because the assessment is about the busiest condition rather than the typical one. Agree that departure in writing before you survey.
School term and holiday effects
The school run is the reason the neutral month convention exists. On residential distributor roads the morning peak is shaped by school journeys, and their removal changes both the height and the timing of the peak.
Two consequences follow for a Transport Assessment. A holiday count understates the base flow, so your modelled junction capacity looks healthier than it is. And it shifts the modelled peak hour, because the sharp 08:15 to 08:45 school peak disappears and the remaining commuter peak sits later.
Where a school sits within the study area, the highway authority will often ask for the count to be taken in term time and for the assessment to address school arrival and departure separately. That is a reasonable request and it is easier to satisfy from a term-time count than to reconstruct afterwards.
Weather, roadworks and other invalidations
A count can be taken in a neutral month on a neutral day and still be worthless.
Heavy rain suppresses walking and cycling and shifts trips to car, which distorts mode share. Snow or ice invalidates a count entirely. Roadworks, a signal fault, a collision or a diversion on a parallel route moves traffic onto or off the surveyed link.
Build three protections into the survey brief. Require the surveyor to record weather conditions and any incidents observed. Require notification within 24 hours if conditions were abnormal. And ask for a check against permanent count data or against a previous survey at the same location, so an anomaly is visible rather than buried.
Automatic counts run over a full week give you the ability to discard a bad day. Manual classified counts on a single day do not, which is the argument for running both: a week of automatic counts for the profile, a manual classified count on a neutral day for turning movements and vehicle classification.
Agreeing the survey with the highway authority
Scope the survey before you commission it, in a short note to the highway authority setting out the junctions to be counted, the survey dates, the periods, the method, and the assumed peak hours.
Include the reasoning. A note that says "counts proposed for Tuesday 14 to Thursday 16 October, term time, no bank holidays, 07:00 to 10:00 and 16:00 to 19:00 manual classified counts at the three junctions shown" invites a one-line agreement. A note that says "surveys will be undertaken at agreed locations" invites a meeting.
That scoping exercise also settles the assessment years, the committed development to be added, and the growth factors. Getting agreement on those before the survey costs nothing. Getting it afterwards frequently costs a re-run.
For smaller schemes a Transport Statement may need no more than a single junction count, but the same neutral month logic applies to it.
Using older counts and growth factors
Counts do not have an official shelf life, and highway authorities set their own expectations. Three years is a common working limit, with five years accepted where the count is factored up and the area has not changed materially.
Growth factors come from the Department for Transport's national trip end forecasts, applied through the standard transport analysis guidance. State the software, the version, the area used and the growth years in the report, because an unexplained growth factor is the first thing a highway officer queries.
Counts taken during 2020 and 2021 sit in a category of their own. Travel patterns in those years were not representative, and most authorities will not accept them as a baseline at all, factored or otherwise. If your only historic data falls in that window, budget for a new survey.
A Parking Survey follows a different set of timing rules again, based on overnight occupancy rather than on flows, so do not assume one set of survey dates serves both.
Programming counts around your submission date
Work backwards. A spring submission needs counts in the preceding September to November window or in March, which means commissioning in the summer. An autumn submission needs counts in the April to June window.
The sequence that works: agree scope with the highway authority eight weeks before the survey window, commission the surveyor four weeks ahead, take the counts, allow two weeks for data processing and validation, then four to six weeks for modelling and reporting. Add contingency for a re-run, because one survey in perhaps ten is compromised by weather or roadworks.
Missing the window has a real cost. A scheme that misses the autumn window waits until March, and a Travel Plan and junction modelling cannot be finalised until the baseline exists. That is three or four months of programme lost to a diary decision.
This is general guidance, not legal advice. Survey requirements are set by the local highway authority, so check the position with them before commissioning. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. Councils usually expect a transport assessment to be prepared by a suitably qualified transport planner, and professional review is strongly advised.
Browse all 66 report types at PlanScope to scope the transport evidence alongside the rest of the application.
Frequently asked questions
Which months count as neutral for a traffic survey?
March, April, May, June, September, October and November are normally accepted, excluding weeks containing a bank holiday or school half term. Tuesday, Wednesday and Thursday are the neutral days. January, July, August and December are usually excluded, along with Easter and the weeks around it, because flows are not representative.
Why is an August traffic count rejected?
Schools are closed and a large share of the working population is away, so flows on most links fall below the term-time norm. A count taken then understates the baseline, which makes junction capacity look healthier than it is, and it shifts the modelled peak hour because the school peak has disappeared from the profile.
How old can a traffic count be before it needs redoing?
There is no fixed limit and authorities set their own expectation. Three years is a common working limit, with five accepted where the count is factored up using national growth forecasts and the area has not changed materially. Counts from 2020 and 2021 are generally not accepted at all, because travel patterns then were not representative.
What invalidates a traffic count?
Snow or ice invalidates a count outright. Heavy rain distorts mode share by suppressing walking and cycling. Roadworks, a signal fault, a collision or a diversion on a parallel route moves traffic onto or off the surveyed link. Require the surveyor to record weather and incidents and to report abnormal conditions within a day.
Should I use automatic or manual traffic counts?
Usually both. Automatic counts over a full week give a flow profile and let you discard a compromised day. Manual classified counts on a neutral weekday give turning movements and vehicle classification that automatic equipment cannot provide. A single manual count on one day gives you no way to detect that the day was atypical.
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.