Gangs of children as young as 10 have been throwing objects at cars travelling along the A45.
Police say there have been four incidents in the past month, with the latest taking place on the A45 near Earls Barton at about 9pm on Sunday.
The victim, who was travelling towards Wellingborough with her husband, said: “We didn’t see anything on the bridge and before we knew there was this piece of concrete hurtling towards us.
“It hit the bonnet first and then ricocheted over. It dented and scratched the bonnet, it’s damaged the wipers and damaged the screen.
“We were very shocked and the noise was just incredible. We were so shocked. There are so many bridges along that stretch.”
She reported the incident to police, but added: “I don’t think there’s an awful lot the police can do. It’s just mindless and they don’t appreciate what they have done.
“It’s only because it’s such a robust car like a BMW that there wasn’t more damage.”
Police went out to the bridge near the Mill Lane bridleway afterwards, but the youths had fled.
Officers were also called out the day before for two similar incidents on the A45 at Riverside, near Northampton, and one on the A45 near Stanwick on February 16.
Police went out on each occasion after reports of children aged between 10 and 14 throwing objects at cars.
A Northamptonshire Police spokesman said: “Throwing objects from bridges onto vehicles which are moving quickly below is extremely dangerous and can lead to serious accidents and even deaths.
“We believe gangs of young children are responsible for these incidents and they and their parents need to know that their behaviour could have very serious consequences both for them and the innocent drivers below.
“The last thing we want to see is anyone losing their life on Northamptonshire’s roads because of the foolish behaviour of children who should know better.”
While these incidents have not resulted in serious injury, it is not the first time this has happened.
HGV driver Laurence McCourt, 68, from the West Midlands died instantly when a breezeblock smashed through the cab of his lorry on the A45 between Wellingborough and Doddington in July 2007.
Police have said they are not necessarily linking the recent incidents due to the different locations, but are keen to hear from anyone with information by calling 101.