The Supreme Court, which heard arguments in November, said in a two-sentence order that it will let an appeals court decision stand in favor of Anthony Owen.
FILE - Generic gavel on wooden table.
Owen pleaded guilty to impaired driving but was allowed to fight the case in higher courts.
The appeals court in 2019 threw out the evidence when Owen's attorney successfully argued that the speed limit actually was 55 mph by default because there was no sign stating the speed limit on Parsonage Road.
When the Supreme Court agreed to hear arguments, it asked if the officer simply "made an objectively reasonable mistake of law."
Indeed, that's how three of the seven justices viewed the case Wednesday, but Brian Zahra, Stephen Markman and David Viviano were in the minority.
A statewide group of prosecutors had urged the Supreme Court to provide clarity for disputes over the Fourth Amendment, which covers searches and seizures.
The appeals court decision "requires not only that every police officer within this state carry all the state's law books within her patrol car, but also that she be able to apply that law within a span of time before a speeding vehicle can get away," the group said. "This onerous obligation is not required by the Fourth Amendment to perform an investigative stop."