I'd say Bennjamin is on the money. I've seen NSW cops doing roadside speed checking, with a camera-like unit on a tripod, behind their car. That's the unit checking rego's, I'm told, and it can do the business, very quickly and have offenders side-of-the-road in a flash. Perhaps, since then, the units have been fitted on car roofs?

BTW, have you ever counted the number of police units used for roadside breath testing - amazing!

CHEERS
NOEL-