When a vehicle is lawfully stopped as a result of a suspected traffic offense, there are three ways, under the Fourth Amendment, that valid consent to search can be obtained: (1) with at least reasonable suspicion of criminal activity, (2) absent reasonable suspicion of criminal activity, when the request for consent to search does not add time to the stop and (3) once the stop has concluded and the officer is engaged in a voluntary contact with the occupant(s).*
In Rodriguez v. United States (2015), the Supreme Court noted that the permissible duration of a traffic stop is determined by its mission. The mission of a traffic stop is limited to those tasks reasonably related to dealing with the traffic infraction (or whatever the lawful basis for the stop is). The Court also noted that officers could also take measures to ensure their safety as a matter of routine. These safety measures could include ordering the occupants to exit or remain in the vehicle and inquiring about weapons in the car. Any law enforcement conduct investigating unrelated matters that adds time to the stop violates the
Fourth Amendment unless the unrelated investigation is supported by at least reasonable suspicion. Asking for consent to search would almost certainly be beyond the scope of a normal traffic-infraction stop as there is no evidence of a traffic infraction that an officer could reasonably expect to find in a vehicle.
Reasonable Suspicion of Criminal Activity
Suppose an officer develops reasonable suspicion of criminal activity during the stop while not adding time to the stop. In that case, the officer can ask for consent to search the vehicle if the crime the officer suspects is the type for which evidence could be found in the vehicle. Once reasonable suspicion is developed, the scope of permissible questioning and other investigative activities expands greatly. In addition, the officer need not resolve the traffic infraction (i.e., issue a warning or ticket) before he begins investigating the criminal activity.
Seeking Consent to Search Without Adding Time to the Stop
The officer can also seek consent to search during the stop as long as the request for consent does not add time to the stop, even without pre-existing reasonable suspicion. If the officer diverts his attention from addressing the traffic matter, even briefly, to ask for consent to search, he has added time to the stop and has thus violated the Fourth Amendment. Accordingly, the seizure has become unlawful, and any subsequent consent is invalid as a matter of law.
But a lawfully detained person can give valid consent. United States v. Watson (1976). If the request for consent to search is asked without adding any time to the stop, the seizure remains lawful. One way this can easily be accomplished is by using a second officer on scene. While one officer is addressing the traffic matter, the Fourth Amendment permits the other officer to engage in unrelated questioning. See Arizona v. Johnson (2009). The second officer is not adding time to the stop because the first officer is still in the process of adhering to the mission of the stop.
Ending the Stop and Transitioning to a Voluntary Contact
An officer can also end the seizure and attempt to transition to a voluntary contact. The officer’s words and conduct must convey to a reasonable person that the traffic stop has concluded and the occupants are free to leave or otherwise decline to participate in conversation with the officer. If the occupants agree to remain and speak with the officer, the officer can ask for consent to search. Again, since the contact is voluntary, no reasonable suspicion is required under the Fourth Amendment.
* Several states, by virtue of state law, impose more significant restrictions upon law enforcement regarding one or more of these three situations. And some of these states do not permit requests for consent to search under situation (2) at all.