Which condition allows officers to search a motor vehicle without a warrant?

The correct answer is that consent from the vehicle owner allows officers to search a motor vehicle without a warrant. When a vehicle owner or driver voluntarily gives their consent for law enforcement to conduct a search, it negates the need for a warrant. This consent must be given freely and can be revoked at any time, but as long as the consent is validly obtained, officers are allowed to conduct a search based on that consent alone.

In contrast, observations of suspicious behavior by a driver may create reasonable suspicion that could lead to further investigation, but it does not automatically grant the authority to search without a warrant. Similarly, routine traffic stops generally involve limited searches known as "Terry stops," which must be justified by specific justifications, rather than blanket authority to search the entire vehicle. Therefore, while all these conditions relate to situations in which a search may occur, consent from the vehicle owner is the definitive condition that permits a warrantless search.