The SCOTUS has limited the ability of the police to continue a traffic stop in order to conduct a search.
The Court reasoned:
Absent reasonable suspicion, police extension of a traffic stop in order
to conduct a dog sniff violates the Constitution’s shield against
unreasonable seizures.
A routine traffic stop is more like a brief stop under Terry v. Ohio than
an arrest. Its tolerable duration is determined by the seizure’s
“mission,” which is to address the traffic violation that
warranted the stop and attend to related safety concerns. Authority for
the seizure ends when tasks tied to the traffic infraction are—or
reasonably should have been— completed. The Fourth Amendment may
tolerate certain unrelated investigations that do not lengthen the roadside
detention but a traffic stop becomes unlawful if it is prolonged beyond
the time reasonably required to complete the mission of issuing a warning ticket.
Read the whole opinion below:
http://www.supremecourt.gov/opinions/14pdf/13-9972_p8k0.pdf