Buddy of mine used to live on a road with 35mph limit and no enforcement. We noticed one day that when I parked my old police car in front of his house traffic slowed considerably.
A couple weeks later, we hung an old microwave burglar alram unit in front of his house, and sat back listening to tires lock up as their radar detectors went off. They'd creap along the road looking for Smokey.
When the cops caught wind of what we were doing, they set up a real radar trap 1/2 mile past my buddy's house, and did a land office business.
The difference in time between 40 mph and 60 mph don't amount to much unless you're going a long distance, and it sure as he!! doesn't stack well against the time you have to work to pay the fine.