Last night on way home from Lower Stoke Winter sing we came off the M25 onto the A12 near Brentwood Essex to be met by several police cars, swerving side to side across the 3 lanes very slowly in order to slow down and stop traffic. We followed the squad car directly in front until he stopped and we noticed that some way ahead the other 2 police cars had come to a halt just before over pass and officers got out and were scanning the road.
They got back in their cars and we proceeded slowly as before until the next over pass, actions repeated as above and at the next, util we got to Ingatestone exit where we were detoured off of the A12.

This might be the reason why.
Concrete attacks: A12 in Essex closed for search

Thinking back I am remembering an incident Charlottesville, VA. I saw a flash of silver falling about 150 yards ahead onto the 4 lane road at about 4.30 am on my way into work (shelf stocking at Roses department store). I was the only car on the road. Given the hour, obviously these people were just on a lark and tossed the trolley maybe just to hear the crash, maybe in hopes a car would strike it. If they meant to drop it onto a car, they would have waited until I was closer to the overpass.

The A12, is the main east to west road in Essex and heavily travelled except in the wee hours of the morning. Even then it can see some traffic as it is the corridor from Harwich (where container ships are off loaded onto lorries) to the M25 and all points beyond. These incidents on the A12 are clearly aimed at passing traffic.

Some very sick individuals out there.