Sometimes they do this on the 101 Fwy heading northbound into Ventura from L.A. in order to close the gap on a group of nine 911s slightly exceeding the speed limit, and they didn't see the police air armada tracking their rate of speed from 5,000 feet. This tactic is an effective method to funnel them all onto one offramp to gift them with speeding tickets.
... as an example. Ask me how I know.
Sherwood