In the 1996 case Whren v. United States, the Supreme Court ruled that it is lawful for a police officer to follow a citizen on the road and pull that citizen over for any traffic violation regardless of how minor the violation is or whether a reasonable officer would’ve made such a stop. (This was a highly problematic ruling because law enforcement officers testified that an officer can ALWAYS find some sort of traffic violation regardless of how good of a driver someone is= its impossible to observe every single traffic regulation).
In addition the Whren court ruled that an officer’s subjective reason for making a stop makes absolutely no difference in determining whether the stop was legal or not; meaning if an officer see’s a person wants to search him because he “looks suspicious” the officer can legally stop him for that reason as long as the officer has probable cause to believe some traffic law has been violated (the officer will always possess such probable cause).
In addition, in Arizona v. Gant the US Supreme Court provided officers with 2 routes to justify searching a car once there is a stop/arrest. Officers may search a vehicle incident to lawful arrest (1) for officer safety=cops believe the arrestee may access a weapon from within the vehicle –OR- (2) cops have reason to believe that evidence related to the crime of arrest is inside the car. This means that once officers make even a minor traffic stop, it can easily escalate into a full-scale drug search of the driver, passengers and vehicle itself.
The practical lesson for today is, know that your right to privacy inside your car is very limited and that police can utilize a host of legal rules to justify stopping you and searching your person, car and all of its contents.