Vehicle speed surveys
A measured picture of how fast vehicles are travelling, written up so a community can use it.
A vehicle speed survey records the speed of vehicles on a particular stretch of road. Parish councils, town councils, schools, residents’ associations and local groups commission one when the conversation has moved past “everyone knows they speed here” and needs something that can be read by someone who was not standing on the pavement.
What a speed survey is
During an agreed period, a KerbSight surveyor records vehicles passing a chosen point. Each observation has a time, a speed in miles per hour, a direction and a vehicle type. The result is a description of that place at that time: the spread of speeds, the average, the 85th percentile, and the share of vehicles at or below the posted limit.
It is an observational survey. KerbSight does not stop vehicles, does not issue penalties, and does not act for the police. A report is independent traffic data and analysis. It is not police enforcement evidence, and it should not be described that way.
Why communities commission one
The usual reason is a concern that has become hard to settle by discussion alone. Speeding through a village. A residential road that feels faster than the limit. The stretch outside a school at drop-off. A route that a planning application will add traffic to. A committee that has been asked for traffic calming and wants to know what it would be asking for.
People who live with a road are often right that something feels wrong. Feeling and measurement still answer different questions. A survey is how a parish council, a school or a residents’ association turns a widely held concern into a set of figures and a written explanation.
What KerbSight measures
- Vehicle speed, in miles per hour
- The time of each observation
- Direction of travel
- A simple vehicle type, so cars are not mixed in silently with lorries and buses
- The posted speed limit, the survey position, the date, the duration, the weather and the road conditions
Where it helps the question, the same visit can also support a traffic count. Volume and speed are related, but they are not the same measurement. A quiet road can still have high speeds. A busy road can be slow.
What you receive
A written report, not a spreadsheet on its own. It sets out the method, the location, the period covered, and the findings in plain language. Typical figures include the mean speed, the 85th percentile speed, the distribution across speed bands, the proportion of vehicles at or below the posted limit, and a split by direction. See reports and data and a sample layout using demonstration data.
Customers will also be able to explore survey results through the KerbSight online portal, so the figures are not trapped in a file that only one person can open.
What the 85th percentile speed means
The 85th percentile is the speed at or below which 85 percent of the observed vehicles were travelling. Fifteen percent were going faster. It is a long-standing figure in traffic engineering because it describes the speed most drivers were choosing. An average can be tugged down by a queue or up by a few very fast vehicles. The 85th percentile is harder to distort in that way, which is why it is reported as well as the average, not instead of the distribution.
It is one number in a report. It is not a verdict that a road is safe or unsafe, and it is not an enforcement threshold. Read it next to the posted limit, the time of day, and the share of vehicles above that limit.
From a concern to measured evidence
Anecdote is a reasonable place to start. Residents notice the car that felt dangerous, the noise at night, the moment outside the school gate. Those accounts matter, and they often explain why a survey is worth doing. They are a poor way to tell a highway authority how fast the traffic as a whole was going, because memory favours the extremes.
A survey does not replace local knowledge. It gives that knowledge a measured companion: this many vehicles, in this period, at these speeds. That is a firmer basis for a letter, a committee paper, or a meeting.
Using the findings
Councils, highway authorities and the police each have their own processes. A KerbSight report does not compel any of them to act, and it is not a substitute for their own evidence where enforcement is the question. What it can do is give a parish council, a school or a community group a clear, independent account to put in front of them: where the surveyor stood, what was recorded, and what the figures show.
The method is described on the methodology page. The report itself repeats the details that apply to that visit, so a reader does not have to take the conclusions on trust.
Repeat and before-and-after surveys
A single survey is a picture of one period. A second survey, on the same stretch and recorded in the same way, shows whether that picture has changed. That is useful after a change on the road, a new restriction, a development, or simply a different time of year. Comparing two anecdotes is difficult. Comparing two surveys is the point of doing them the same way twice.
Common questions
What is a vehicle speed survey?
A vehicle speed survey records the speed of vehicles passing a point on a road, usually together with the time, the direction and the type of vehicle. It describes what traffic was doing during the survey. It is not enforcement, and it does not by itself decide whether a road should be changed.
What does the 85th percentile speed mean?
It is the speed at or below which 85 percent of the observed vehicles were travelling. It is widely used in traffic work because it reflects the speed most drivers were choosing, without being pulled around by a few very slow or very fast vehicles. KerbSight reports it alongside the average, the distribution, and the share of vehicles at or below the posted limit.
How is a survey different from a complaint that cars are speeding?
A complaint describes what people have noticed and how the road feels. A survey measures vehicles over an agreed period and sets the result out so someone else can read it. Both can be sincere. They are not the same kind of information.
Will the police use a KerbSight survey for enforcement?
No. KerbSight does not carry out enforcement, and a KerbSight survey is not police enforcement evidence. A measured picture of a road can still help a council, school or residents’ group describe a concern to a highway authority or to the police.
How long does a speed survey last?
It depends on the road and the question. A short session can show a particular time of day, such as the school run. A longer survey shows how speeds change through the day. The duration is agreed before the visit and stated on the report.
Can a survey be repeated?
Yes. A later survey on the same stretch, recorded in the same way, is the straightforward way to see whether speeds have changed after something on the road has changed, or at another time of year.