I was riding on a school driveway heading to the main road, parallel to that driveway was another driveway. A police cruiser was headed in the same direction, I was waving my arm both to say hello and for him to stop. I reached the main road before him, I turned left onto a sidewalk going in front of his vehicle, at the same time I'm still waving. Windows were dark so I couldn't make eye contact, I thought sure with all my arm waving he saw me. Evidently not because just after I cleared his bumper he started going, he never saw me and never looked right before driving (it was a split road no traffic would be coming from the right). No harm done but it was too close for comfort, I know he had a surprised look on his face, probably eye opening for him.