Anywhere in the country, including Washington, law enforcement officers have the authority to stop motorists and anyone else using public roadways. Police authority, however, is not unlimited and cannot violate an individual's civil rights without due process. An officer can stop and search a person but only when there is probable cause for such a search.
That limitation recently played itself out when the Washington Supreme Court ruled that a September 2011 search by police was unconstitutional and thus a drug conviction was not valid. According to court documents, a Centralia police officer pulled a cyclist over for a minor traffic violation. The man was frisked, which the court ruled was allowable. The officer found a small box in one pocket of the man's pants and opened it. The officer allegedly found a syringe containing methamphetamine. The man was arrested and charged with drug possession.