Four cars were damaged and the drivers were left shaken by the attack on the M80 near Robroyston, described by police as "frankly idiotic."
Three males, believed to be teenagers, stood on the railway line above junction 1 and 2 and threw the bricks and large stones at cars travelling north at around 4pm on Tuesday.
One of the cars had its windscreen on the drivers side badly damaged.
The suspects are described as in their teens and wearing black.
Police are urging anyone with information to contact them.
Constable Hugh Niccolls, Divisional Road Policing Unit, Glasgow, said: "Thankfully no one was injured as a result of this quite frankly idiotic act, however, it could have been so much worse. I cannot fathom why someone would do this.
"Do they not realise or indeed even care about the danger they put people in.
"We are currently checking CCTV to identify those responsible for this criminal behaviour and I would appeal to anyone who saw the boys on the line, or has any information that will help us with our inquiries to contact police on the non-emergency number 101."
Information can also be passed in confidence to Crimestoppers on 0800 555 111.