I've seen similar boxes as you describe which have 2 parallel rubber hoses coming out across the road, when you drive over each hose it acts as a preassure switch so they can tell the direction and speed you're travelling - i.e: used for traffic/speed monitoring not speed enforcement. Maybe they haven't attached the hoses yet?
If it's these it sounds like they're planning something local to you, more houses, a new billboard (market research), a new by-pass, new road layout... that kinda thing. Maybe a traffic calming type road layout to save the cost of the police hanging around doing speed checks.