There must be probable cause or reasonable suspicion for a police officer to initiate an investigatory stop of a vehicle. Absent a warrant for a search or arrest, there must be some basis known to the officer for believing an occupant of a vehicle may have committed or may be about to commit a crime, before the officer has the authority to selectively detain the vehicle for even a brief investigation. In the recent case of State v. Mackinnon, E2012=00594-CCA-R3-CD (Tenn.Crim.App. 5-29-2013), the Tennessee Court of Criminal Appeals upheld the trial court's finding of probable cause where a trained police officer estimated the Defendant's vehicle to be speeding.
An estimation of the speed of a vehicle in ordinary use can be made by a lay witness in Tennessee courts. In the Mackinnon case (which ultimately resulted in a conclusion of violation of the implied consent law), the officer who initiated the stop of the Defendant's vehicle testified he had been trained to observe and estimate the speed of moving vehicles, without relying upon radar equipment. Part of that training included having to observe and estimate the speed of two hundred moving vehicles and be accurate within two miles per hour. The officer estimated that the Defendant was driving fifty-three miles per hour in a thirty-five mile per hour zone. In determining that the officer had probable cause to stop the Defendant for speeding, the trial court relied upon this testimony. The Court of Criminal Appeals affirmed the ruling on this issue.
In this case, the Court did not reach the question of whether the evidentiary exclusionary rule applies to evidence of violation of the implied consent law (which is not a criminal conviction and does not carry a jail sentence, but only an administrative penalty), as the probable cause finding resolved the issue this time.
For more information on what evidence may be required to justify a stop and/or detention of a vehicle by government authority, contact Hindman & Associates.