What is the law on traffic stops?

First of all, automobile stops are considered seizures; and the decision to stop an automobile is reasonable where the police have probable cause to believe that a traffic violation has occurred (speeding, running a red light, etc.). However, a stop that extends beyond the scope of the traffic stop is a seizure and must be grounded in new reasonable suspicion unrelated to the basis for the original stop. In other words, if the officer finishes writing the ticket, but holds onto the license, and then begins to ask questions about other matters, a seizure has occurred, and the officer must have reasonable suspicion to continue the detention. However, if the officer hands back the license and continues to ask questions, whether there is an actual seizure depends on the circumstances, i.e., is the motorist technically allowed to leave or is the motorist answering questions consensually.