A routine traffic stop is a “seizure” under both the Fourth Amendment to the U.S. Constitution and Article 14 of the Massachusetts Declaration of Rights. Accordingly, police must have a legal justification for pulling you over.
So when exactly are police justified in stopping a motorist?
According to the Supreme Judicial Court,
A police stop of a moving automobile constitutes a seizure and, therefore, must be reasonable in order to comply with the Fourth Amendment and with art. 14. We consistently have held that a stop is reasonable, and therefore constitutional, where an officer has observed a traffic infraction and, as a result, has actual cause to believe that the driver violated an applicable motor vehicle law. We have applied this test, often referred to as the authorization test, without regard for the gravity or magnitude of the perceived violation.
Commonwealth v. Larose, 483 Mass. 323, 326-327 (Citations and quotations omitted.)
Evidence seized following an “unreasonable” stop can be barred from subsequent court proceedings by a defendant’s motion to suppress.