You'd be surprised just how good the user reporting is. I took a 7-hour drive through Ohio with a friend who has a very expensive, supposedly "detects everything" radar detector. We used Waze for the entire trip, as well. During that trip, Waze spotted every single police officer. I'm not sure what was going on, but there was a cop hidden about every five to ten miles on the trip -- something I've never seen before, despite trekking through Ohio on more than a few occasions[0]. His very expensive radar missed many of the cops (maybe they weren't firing the laser? who knows). The best part, though, was when we hit the Cincinnati and his radar had to be silenced due to all of the false positives it kept throwing. There was one false positive with Waze, which was barely a false positive as it was clear the police officer had moved and there were simply two entries for the same cop.

Yes, it's fool-proof to simply "not speed" and I have Waze set up to give me speed warnings so that I avoid speeding by accident. The fact of the matter is, traffic laws are the kinds of laws that are easy to break by accident. Getting a little extra warning to pay attention, both in having a speed warning and an enforcement warning, is helpful in avoiding a costly mistake. And there are times when speeding is the safer choice. In Michigan, interstates are almost all 70 MPH (with, I'm told, some going to 80 MPH). Around cities, where acceleration/deceleration ramps are too short and for a variety of other reasons related to the design of the freeways, the speed limits are set at 55 MPH. Everyone continues to travel at 70 MPH. Aside from the concept that keeping at the same speed of traffic reduces the speed at which you are hit in an accident (70 MPH, 75 MPH collision is 5 MPH at initial impact plus whatever happens after that), the bigger problem is the aggressive drivers, many of which are simply going the expected 70 MPH (some, probably without realizing the speed limit dropped) who will jump out of your lane, cutting off the driver in the adjacent lane, then jump back in front of you, similarly failing to leave a safe distance. This lane-jumping causes at least three different opportunities for a wreck should every driver involved not be paying appropriate attention.

About a decade ago, I watched exactly how this can turn into an incredibly dangerous situation. The slow car was in the right-most lane, traveling at 55 MPH on I-94. The road had moderate traffic and the van approached the smaller car at around ... probably ... 75-80 MPH. He had a sedan behind him pretty close traveling at the same speed. The van didn't want to slow down but there was a car in the middle lane, so he accelerated and managed to get in front of a car in the middle lane by getting maybe a foot off of the bumper of the slow car and rapidly changing lanes. The car behind the van wasn't so lucky. I'm guessing he was fiddling with the radio or phone, because he didn't react fast enough (though I'm not sure if he had reacted fast enough that the accident would have been avoided). He slammed on his brakes while simultaneously attempting to dodge the smaller car by moving to the left, hitting the car that was nearly blocking the van and the small car in front of him. By the time it was over, there was a rollover (the car behind the sedan who had chosen to swerve right -- onto the shoulder -- and swerved too hard), the middle lane car was totaled and several cars were rear-ended. Luckily, nobody died (as far as I know) but a few were taken off in ambulances. The slow car had the sedan nearly in its back-seat (I'm guessing he did the instinctual thing and slammed on the brakes when he got hit, making the damage worse). I was in the left-most lane and narrowly avoided both hitting the guy in front of me and being hit from behind. We all had a helluva morning giving statements to the police.

The best advice my dad gave me when I was 15 years old and learning to drive was "accidents are caused when you do something that other drivers aren't expecting." On the freeway, other drivers are expecting that every car is traveling very near the speed of everyone else. When you're the car who is not, you're "the unexpected". The good news is, according to anecdotal accounts I have from family members who are cops, the police understand this, too, and will generally not just pick a car out of the mass of vehicles going too fast. They're specifically looking for the guy who's jumping lanes or going at a much higher rate of speed than the rest of traffic.

Incidentally, the one thing you can count on when there is a cop monitoring one of those 55 MPH areas is that right near that cop, there's going to be a lot of sudden braking. Getting an audible warning of that a half-mile before it happens -- avoiding a possible fender-bender -- is really helpful.

[0] And it wasn't just Ohio, I-75, I-275 in Michigan as well as I-94 leading all the way up to Canada were similarly crazy.