It's proably been covered here , but if it hasn't there is an app called waze and it is by far the absolute most accurate thing I have ever used.
It called with 100% accuracy 6 speed traps & 3 disabled vehicles on my weekly 100 mile run to get cigarettes and other tax free goods in NH.
check it out, judge for yourself.
https://www.waze.com/

 

It legit works? Like if theres a cop parked somewhere taking speeds, the app tells you before you pass them? Ive tried these kind of apps (not this one) before and none seem to do anything lol

 

My wife has waxed on her iPhone and it's great. But as for the data like cops, accidents and such, that is data entered by the users of the app that are on the road and as you pass something flagged it does give you a chance to confirm if the item is still on the road or not.

As for the cop sighting on waze, keep in mind, someone has to be the first to see the cop and flag he's there and you might be that first person.