| Rockhopper
The van you describe is an ANPR vehicle. These are not speed detection units but vehicles with on board camera systems that will read a number plate and should there be a "note/referance mark" asociated with that vehicle it will be stopped further down the road. The "mark" can be referenced from a local data base from within the vehicle or from a live link to the PNC via a mobile phone systen.
These vans have multiple uses and many of them can be linked together, although deployed remotley from each other, so as to detect and keep a trail of the movements of a known or wanted vehicle..
A cleaver bit of kit actually |