One complainant was a truck driver who was hit by a large rock on the windscreen, thrown by the young people from the bridge over the E4.
The police went to the scene with a patrol, but could not find the culprits.
It is classified as vandalism, but press spokesman Magnus Jansson Klarin at the police says that it could have gone bad.
- It can be very serious if you get a big rock on the box, he says to SVT.