Police stopped Nicholas Johnson, 22, after he revved his pickup truck in response to friends who mooned him at a traffic stop.
An officer smelled alcohol and arrested Johnson, who had a blood-alcohol level of 0.13 percent, above Utah's legal threshold.
But defense attorney Glen Neeley claimed the officer had no probable cause to stop the pickup truck last September in North Logan. First District Judge Clint Judkins agreed.
"We're not a police state yet," Judkins said Wednesday. "Revving your engine is not illegal.
"This has to be looked at through two windows. The first being that the police officer was on the street simply doing his job, the other is a person's Fourth Amendment right," the judge said, referring to an unreasonable search.
