Police have warned that motorists could be killed after a spate of incidents in which cars were bombarded with lumps of concrete from a bridge over the M1.
Six vehicles have been damaged in the last two weeks
Six vehicles have been damaged in the last two weeks after being hit by debris thrown from the Green Lane bridge at Worsborough, near Barnsley.
In one incident, a car sun roof was smashed, showering a couple and their two children with shards of glass.
Police said: "We're extremely lucky not to be dealing with a fatality."
On the night the family escaped serious injury last Tuesday, a lorry driver suffered cuts and bruises when a piece of concrete smashed through his windscreen and hit him on the shoulder.
A second car had a piece of concrete embedded in its windscreen showering the driver with glass. Two other cars ran over debris in the road and suffered tyre blow-outs and suspension damage.
In the early hours of 30 June, a vehicle sustained "substantial damage" when it was also hit by concrete.
In all the cases, the vehicles were travelling at between 50 and 70mph.
Pc Nigel Heritage, from South Yorkshire Police, said: "Any of these missiles could have struck the occupants of the vehicle in the head and could quite easily kill the driver and occupants of the vehicles, along with other road users.
"We are appealing for anyone who witnessed the people concerned committing these dangerous acts to contact the police.
"We would also like to hear from anyone who has any knowledge as to who the perpetrators may be.
"It is essential that we stop these people before they cause serious injury or maybe even loss of life to a motorist."