Why does the Highways Agency use ANPR?

The HA cur­rently oper­ates 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 the High­ways Agency’s net­work and enables the NTOC to com­mu­ni­cate this to the trav­el­ling pub­lic through ser­vices such as Traf­fic Eng­land.

The High­ways Agency’s 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 the 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 the High­ways Agency’s ANPR cam­era 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, the High­ways Agency 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. The High­ways Agency 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.