Here is a great video that describes the operation of a mobile speed photo enforced van in Chicago. There are five photo enforcement vans across the state of Illinois. The speed enforcement vans proved more effective than placing electronic radar signs on the highway shoulder to show drivers their real-time speed, or even deploying police cars to sit on the side of the road, the research found.

The Illinois State Police photo vans are capable of identifying scores of speeding scofflaws across multiple lanes of traffic in only a few minutes, ringing up minimum $375 speeding tickets that are sent in the mail for the work-zone violations. It's a process law-enforcement officials say is much more efficient—and safer for police officers—than pulling over individual speeders as traffic rushes past.

In addition, it's a mystery to drivers how much leeway is given above the 45 m.p.h. construction zone speed limit. Does going 50 m.p.h. trigger a ticket, or do you have to be speeding at 10 m.p.h. above the work zone speed limit? The answer changes from one jurisdiction to another.