Police
Sorry to upset all of the folks asking for more features to warn of police presence but this is a childish feature which should be removed. Waze is a great app and you would be best served by taking the "high road" and promoting the app as an aid to road safety by making drivers aware of road situations and hazards. But many wazers like me have their kids also driving and I am just waiting with dread for the day that a fellow wazer tells a drunken driver how to avoid a policeman and then that drunk driver kills the wazer's kid. The police are mainly there for our safety - protect our kids and don't tell dangerous drivers where the police are!!

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Rob commented
You could extend this argument to speed cameras too - speeding drivers may also cause accidents. But let's be fair, the police are usually in attendance because there is an incident, which may be a distraction to other drivers, or mean that there are increased numbers of pedestrians or other road users likely to be in a vulnerable position/state. In addition police cars often stop obstructing the highway, so there is almost certainly going to be a traffic issue too.
In my opinion, the benefits of having this information outweigh the likelihood of it being abused and remember, whilst the data appears in realtime, it is not guaranteed to be 100% accurate, police cars may move, or remain undetected.
Also, consider the psychology of drink-driving, the possibility of being caught by the police has already been discounted by the driver, I would not imagine they consider evasion to be a priority over getting to their destination via the shortest or least complex route.
Waze is not designed to help drunk drivers it is designed to help communities. If you believe drink driving is a particular issue in your community, you should work together as a communtiy to address it.
Now, add the ability to track bad/drunk drivers on Waze and you might be on to something.