Police are hunting yobs who threw stones at cars from a bridge in Sunderland.
Three cars were damaged after stones were thrown from a bridge across Tunstall Hope Road on Monday.
Vehicles were also swerving to avoid the stones.
Police are warning the anti-social behaviour could have had serious consequences and urging anyone with information to come forward.
Neighbourhood Inspector Tony Carty said: "Throwing objects onto busy roads is reckless and incredibly dangerous. The objects do not need to hit a vehicle to cause damage - vehicles are swerving to avoid being hit by the falling stones which could cause a serious collision.
"Not only that, but the very shock of an item hitting the carriageway could cause a motorist to lose control of their vehicle.
"Youths may think it is a bit of fun but they need to be aware of the danger they are causing, we are carrying out enquiries to trace those responsible and we will take action against them. If it's found their actions were directly responsible for causing a collision there will be serious consequences.
"We'd also like to ask parents to reinforce this message and remind their children of these dangers.
"If anyone has any information that can help in our enquiries then we would encourage them to come forward and pass this on to us.
"We know it's a handful of young people who are involved and I'd urge anyone with information or who witnesses any offences take place to let us know as soon as possible."
Northumbria Police and Crime Commissioner, Vera Baird DBE QC, said: "This behaviour is completely mindless and has the potential to cause serious harm. Those responsible need to be made aware of the consequences, which are very serious.
"Ensuring Northumbria Police tackles anti-social behaviour and tough and effective action is taken against those who are responsible for unwelcome trouble and disorder remains a top priority for me. My message to people in Sunderland is – if it’s a problem in your community – report it."
Anyone with information should contact police on 101 quoting reference 778 010517 or the independent charity Crimestoppers on 0800 555 111.