Motorway snowballs 'could kill', Hertfordshire police warn
People throwing snowballs onto the A1(M) in Hertfordshire could cause "multiple fatalities" and will be prosecuted if caught, police have warned.
Two windscreens have been cracked on vehicles passing under the Norton Road bridge at Baldock, police said, with people seen throwing large snowballs.
Insp Danny Lawrence said the drivers' lives were put at "serious risk".
He added more officers were patrolling the area to try and find the culprits.
Insp Lawrence said: "The offenders put these drivers at serious risk and could have caused someone to lose their life or even caused multiple fatalities.
"We will be stepping up patrols in the area and will be working hard to trace the suspects whose behaviour could be described at best as utterly reckless and without any regard for the safety of innocent members of the public."
The Met Office has issued a warning of widespread ice in Bedfordshire, Buckinghamshire and Hertfordshire as temperatures are expected to remain at freezing level throughout the day.
Most schools have reopened after 860 closed in the three counties on Monday.