Why does Highways England use ANPR?

We currently operate an ANPR (Automatic Number Plate Recognition) camera system through the National Traffic Operations Centre (NTOC) with around 1,100 cameras. These cameras can be identified by their bright green casings, and are spread across around 500 sites on motorways and trunk roads. The data gathered is used to calculate journey times across our network and enables the NTOC to communicate this to the travelling public through services such as Traffic England.

The ANPR cameras read a Vehicle’s Registration Number (VRN) as vehicles pass them. The number plates are immediately converted though a mathematical process (known as hashing) into non-unique reference numbers (known as tags) at the roadside and the same number plate will generate the same tag on every pass of a NTOC ANPR camera. It is not possible to accurately derive the original number plate from the tag which is not unique to a number plate i.e. a number of different number plates can produce the same tag. The system presently records about 14 million tags a day and the ANPR camera system transmits the following data to the NTOC at 5 minute intervals:

  • the hashed Tag
  • the time the Tag was registered
  • country of origin (derived from the original plate)
  • site number of the ANPR camera

The camera system does not transmit:

  • images of the driver
  • images of the vehicle
  • images of the license plate
  • the ‘original’ number plate characters

Through matching these tags at consecutive cameras the NTOC can derive a journey time between those two points.

Frequently asked questions

How long do you keep data for?

As the data is non personal information (due to the non-unique tag format) there are no Data Protection restrictions on how long we keep it. Currently, the data is kept indefinitely for modelling the network effectively and anticipating drivers’ behaviour in response to incidents on the road network.

Do you provide the data to third parties?

No. The data is only collected for the NTOC to model the network effectively through the calculation of journey times.

Do you send data to the police?

No. The non-unique tag data obtained from our ANPR cameras is only transmitted to the NTOC over secure data networks.

Do you support the police in other ways?

In common with the statutory duty of any public body, we will provide assistance to the Police in the investigation of specific serious crimes (typically those which carry a life sentence). The hashing process creates a non-unique tag that may consequently apply to a number of vehicles. We cannot therefore be definitive about a specific vehicle, and can only say whether or not one or more vehicles with that non-unique tag was observed at the location and within the specified time parameters.

Can the cameras search for specific tags?

No. The cameras record what passes them and send that data to the NTOC at 5 minute intervals.

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