Entering 57 south from eastbound on Yorba Linda Blvd (coming away from Associated), there is a service road in between the bushes on the left side of the road. The author of this post has observed either CHP (especially), Fullerton, or CSUF Police units parked on this road perpendicular to the entrance lanes, watching vehicles. This usually occurs around rush hour, when the metering lights are on. They may or may not be checking speeds, although they certainly are watching for motorists illegally using the diamond lane. Since they do hide out of immediate view, I believe this qualifies as a trap of some sort.