It would really depend upon state laws but in general the driver or person responsible would ultimately be the one that caused the debris to be in the roadway.

So if a metal pipe fell off of a truck and the car in front of you ran it over and "spit it" back up so that it hit your vehicle, it would be the truck that lost the pipe that was negligent. The person in front of you could also have damage so it would appear that they were unable to safely miss the debris in the roadway and that is why they struck it causing it then to strike your car.

Thus if the negligent driver that lost the debris could be found then normally they would be responsible since it was their item that caused the damage to be sustained to others. In some states they may only be found at fault though if was due to negligence that caused the item to be dropped on the roadway.

If the person leaving the debris was not found then usually you would need to make a claim with your own physical damage coverages for the damages your vehicle sustained in an incident such as this.