Bricks and stones were thrown from a bridge onto cars and lorries on the M62, leaving them badly damaged.
The incident happened on Tuesday, May 21 between 8pm and 10pm around junction 33 (Ferrybridge) of the M62 Eastbound.
Police received several reports about people throwing bricks and rocks from a nearby bridge.
They were also throwing them from the side of the road.
Five vehicles have been damaged, including cars and lorries.
Officers from West Yorkshire Police have branded the incident "reckless" and "irresponsible."
They also warned that it could have been life-threatening.
Sam Grodecki of West Yorkshire Police is investigating the offences and said: “This irresponsible and reckless behaviour could easily have resulted in a life-threatening scenario and it is only through sheer luck that nobody was badly injured.
“Their mindless actions on one of the busiest stretches of the regions highways is totally unacceptable and it is important that we trace the individuals responsible.
“I don’t need to spell out what could have happened here, nevertheless, it has left a number of cars and lorries badly damaged and their occupants particularly shook up by their experience."
"If you were driving from the A1 onto the M62 around Knottingley and saw those involved, we would like to hear from you, particularly if you have in-car recording devices that may have captured their identity.”
No suspects were found.
Police are now are appealing for witnesses who saw what happened or who may have information about those responsible to come forward.
Anyone with information is asked to contact the non-emergency number 101 or Crimestoppers in confidence on 0800 555 1111.