Five teenage boys have been arrested after four vehicles were hit by bricks thrown from a footbridge over the M25 at Waltham Abbey on Tuesday.
Police were called at about 6.25pm after drivers reported their vehicles being damaged.
The windscreens of two heavy goods vehicles and a recovery truck were damaged and the cab roof of another recovery truck was also hit and slightly damaged. No one was injured.
Detectives are now investigating all the incidents but it is thought that other vehicles were struck by bricks but drivers have not yet contacted police.
The incidents happened near a pedestrian footbridge close to Lodge Lane between junctions 25 and 26.
Five boys, all aged 13 and from Waltham Abbey, were arrested on suspicion of causing criminal damage with intent to endanger life.