How these figures are measured
Every speed on this site is a real reading from a sensor in the road surface, not a model, an estimate or a prediction. This page says which sensors, over what period, and what each reading is compared against, so you can decide for yourself how much weight to put on it.
Where the numbers come from
National Highways runs a network of sensors in the surface of England’s motorways and major A roads, known as WebTRIS. Each one counts vehicles and records their average speed in fifteen minute blocks, all day, every day. Those readings are published as open data under the Open Government Licence v3.0, which is what allows them to be republished here.
This site uses 417 of them across 41 roads, covering 1 May 2026 to 15 June 2026. Readings are grouped by day of the week and hour of the day, so what you see is the pattern a road typically follows at, say, four on a Friday afternoon, averaged across every Friday in that period.
What “slower” is measured against
Each sensor is compared against its own free-flowing speed, never against the 70 mph limit. That matters more than it sounds. Plenty of sensors sit on bends, slip roads and approaches that never see 70 even at three in the morning. Measuring those against the limit would invent congestion that is not there, and would make the quietest stretches look like the worst ones.
So when a page here says a road runs 30% slower than normal, it means slower than that particular stretch normally manages, not slower than some national average.
What is deliberately thrown away
Empty roads in the small hours
A sensor reading 35 mph at 11pm while carrying 129 vehicles an hour is showing overnight roadworks or an empty carriageway, not a traffic jam. Any hour carrying fewer than 600 vehicles is excluded before anything is called a road’s busiest hour. Without that rule this site would confidently report the motorways as jammed at midnight, which is false.
Three in the morning, in the headline answers
When a page names the quietest time to travel it only considers 06:00 to 22:00. The small hours are the fastest on almost every road in England. That is true, and it is useless for planning a journey, so it is not offered as an answer. Those hours are still shown in the full hour by hour tables, just quietened down.
Sensors that are not really reporting
Roughly one sensor in eight returns a full set of empty readings rather than an error, which looks like perfectly good data until you count it. Every sensor is checked for how much of its window it actually filled, and the failures are dropped rather than averaged in as zeroes.
How junctions are named
The sensor data contains no place names at all. A sensor is a code and a pair of coordinates, nothing more. Where this site names a junction, that name has been worked out from the coordinates, by finding the nearest motorway junction recorded by OpenStreetMap contributors, and the surrounding district from postcodes.io. 392 of the 417 sensors could be placed that way.
Because that is a derivation rather than something National Highways stated, the distance is always printed next to the name. “About 600 m from junction 6” is a claim this site can stand behind. “At junction 6” is not, so you will not see it written that way. A sensor more than three kilometres from any junction is left unnamed rather than guessed at.
What this is not
It is not live traffic. The sensor archive runs a few months behind, so these are patterns rather than current conditions. Live closures and roadworks are shown separately and are current. The congestion figures never are.
It does not cover accidents. The National Highways live feed publishes roadworks and lane closures only. There is no accident feed available to this site, so it never claims one.
It cannot tell you about today. An archive describes what usually happens. It has no idea whether there is a collision on your route this afternoon. Check live conditions before you set off, and never check them while driving.
It does not cover local roads. Only the strategic road network carries these sensors. A road that is not here has no data, which is not the same as a road that is clear.
Licence and credit
Speed and volume data is published by National Highways under the Open Government Licence v3.0 and is credited on every page. Junction names come from OpenStreetMap contributors under the Open Database Licence, and districts from postcodes.io under the Open Government Licence. None of those organisations endorse this site, and none of them have checked it.