Washington state law (RCW 46.63.030) allowed police to issue a ticket for a traffic infraction that they don't actually see, but have good reason to think occurred. There's some gray area here, and a Washington Supreme Court decision out today in Washington v. Andrew Magee shows how it can play out.
The time was April 2005 and the place State Route 512, a four-lane divided highway between Lakewood and Puyallup. State police fielded calls that someone was driving the wrong way on the highway. The court decision describes what happened then:
When the trooper arrived, she found Magee parked facing the wrong direction on the shoulder of the SR 512 on-ramp, nose to nose with another vehicle. Magee explained that he had been called by a friend whose car had broken down and that he was there to help jump-start the car. In order to more easily facilitate the jump-start, Magee told the trooper that he had turned his car around and pulled in front of his friend's car on the shoulder. There is some dispute, and the record is unclear, as to exactly how Magee maneuvered his car and whether he backed it down the on-ramp or turned it around on the shoulder. But
Magee contends he never traveled the wrong direction on the traveled portion of the road. Although the trooper never actually saw Magee driving, she concluded that Magee must have driven against traffic in order to reach his position and issued him a notice of infraction for negligent driving in the second degree.
Lower courts said that the trooper's issuing the citation was correct, or at least within the law. The Supreme Court threw it out: "the State argues that the trooper actually witnessed the citable offense because the negligent behavior was 'ongoing.' But negligent driving in the second degree is a moving violation. For the infraction to be valid, the movement must have been made in the officer's presence. Magee's driving occurred before the trooper arrived, the trooper never saw Magee operating his vehicle negligently, and none of the other circumstances outlined in RCW 46.63.030 were present. The trooper did not have authority to issue the notice of infraction."