Images of the aftermath clearly show the windscreen of the large lorry smashed where the sandbag hit, close to where the driver was sitting.
The driver had managed to pull over onto the hard shoulder of the M62 near Tingley, police have said, despite the damage to the windscreen.
West Yorkshire's Road Policing Unit, on Twitter, described it as a "shocking incident".
"A sandbag was thrown from Thorpe Lane over bridge onto this HGV which was travelling on the M62," they said.
"The driver managed to safely move vehicle over to hard shoulder and suffered minor injuries - this could have resulted in a fatality."