Rav Tachan began discussing reckless drivers saying there is a mitzva to report such drivers as they have the status of rodef on the roads. It is not allowed to report reckless drivers, it is an obligation to report reckless drivers. Also, if you capture reckless driving ona  dashcam it is a mitzva to report it to the authorities.

What about reporting the presence of police in Waze so other drivers know police are in the area to slow down in advance or drive safer (eg put away the phone they are using, etc) - on the one hand when you report police presence it causes drivers to slowdown, which is a good thing. On the other hand, reckless drivers will use it to avoid punishment and will continue driving recklessly with nothing to deter them.

Rav Tachan paskened that the purpose of the police presence on the roads is to ensure safe driving. Helping people avoid the police is problematic. It is prohibited to help a reckless driver avoid the police and to avoid the law. Better that he should be arrested, pay his fine and learn his lesson than continuing to drive recklessly..

When someone is putting the public in danger, the concept of "moser" does not apply. A person driving recklessly can be reported without any concern of being considered a moser as he is putting the public at risk.

I would further ask, is it ok to report police as being present on a road even when they are not so as to cause reckless drivers to drive safer?