well the answer is this, they are driving on public roads, those roads don't belong to them, they are allowed to use the roads as long as they obey the laws enacted by their state and local municipalities. Cops patrol those roads and anyone can be questioned who choose to use them. It's why they have a job. So yes one forfeits their rights if they violate their use of them. Your car is not your house on your property, it is on the public's property and suspicious behavior will incite a search. Don't speed, don't run red lights or stop signs, don't drive erratically. It's actually quite simple.