These van's are mostly in Scottsdale and Tempe, and the highway ones are rare (more often you see them on surface streets). The whole idea is stupid and in my mind more dangerous then having officers actually patrolling the streets.
Drivers do the exact same thing they do when approaching a speed camera - slam on their brakes, roll past at 0-5 over (the cameras are tripped at 11 over supposedly), then speed back up to 8-15 over. IMO, these fluctuating speeds are more of a safety hazard then a fast (but steady) speed.
Yet there's an officer sitting at every construction zone. Glad they're being productive.
