A van driver narrowly missed being hit by a large lump of concrete thrown from a bridge during a string of incidents over four days, police have said.
The vehicle's bonnet was destroyed and police said the consequences of the attack in Talavera Way, Northampton, on Thursday could have been "catastrophic".
It was the third report police had received of youngsters launching items from bridges on to the busy A5076 over the last few days, leading them to plead with parents to talk to their children about the dangers.
"This behaviour might seem like a prank or dare to young people, but it could easily kill someone," said PC Polly Scott, from Northampton's neighbourhood policing team.