I think the Police should get involved in Ticketing those people who throw stuff out of cars. This is exactly what is done by the police in many Civilized Countries.
My brother made the mistake of tossing out a water bottle on the Expressway in Virginia, US - (Motorway), the police saw it, and followed him in SILENT MODE for 1 mile, then stopped him, told him to WALK ONE MILE on foot, pick up the bottle, WALK back the whole MILE, and put the bottle inside the car, and toss it in garbage bin, when he reaches home and I think he was given a traffic ticket (fine) too.
Now my younger brother never throws anything out the window. I never did myself, and always stick to that rule, even when I am in Pakistan.
A tough lesson learned by my brother. Same thing needs to be done in Pakistan. The POLICE needs to get tough on people, give them Traffic Violation ticket, as it is against the rules of the traffic, to throw anything out of the car.