Trooper’s Mistake of Law Can Not Give Him Probable Cause to Stop Vehicle

In a recent decision, the Superior Court of Pennsylvania held that a trooper did not have probable cause to stop the defendant’s vehicle when the defendant changed lanes less than 100 feet after activating his turn signal.

In Commonwealth v. Slattery, the defendant Slattery was driving on Route 30 when the trooper spotted him merge from the right lane to the left-turn only lane almost immediately after activating his turn signal. Slattery then turned left, and the trooper followed him and initiated a traffic stop. The trooper testified that Slattery exhibited signs of impairment, and Slattery admitted that he had recently smoked marijuana and that his license was suspended. Slattery was arrested for DUI, but filed a pre-trial motion to suppress evidence because he claimed the trooper did not have either probable cause or reasonable suspicion to stop his vehicle. The court denied this motion, and Slattery was subsequently convicted of driving with a suspended license and turning without a signal, and sentenced to 50 days in jail and a $1,025 fine.

Slattery then appealed this decision, claiming that he did not violate any sections of the traffic code, and consequently the trooper did not have probable cause to pull him over. The relevant statute stipulates that a driver must use their turn signal before switching lanes, and a different section of the same statute provides that when a driver is traveling at less than 35 mph (as Slattery was), he must activate his turn signal at least 100 feet before making a turn. The trooper testified that he had probable cause to stop Slattery because while he had activated his turn-signal before switching lanes, he hadn’t done so at least 100 feet before switching lanes. However, the statute clearly states that the minimum distance requirement only applies to turns onto a different street, and that there is no minimum distance requirement for using the turn-signal before switching lanes.

Because of the trooper’s mistake of law, he did not have probable cause to stop Slattery. Consequently, the stop was unlawful and the Superior Court held that any evidence flowing from it should have been suppressed. The Court then reversed the judgment against Slattery and remanded the case for a new trial.

Here is a copy of the court’s complete opinion.

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