To cover the damages your vehicle received in the accident you would need collision coverage. Property damage liability held by you and your friend will not cover the damage your friend caused to your vehicle in this single car accident.

Liability covers you if your car damages someone else's property, in this instance the guardrail. Liability insurance does not cover your car for damages you or another driver cause when operating it, it instead covers the property that you hit.

Since your friend hit a guardrail in your car then you may receive notice from your state's Department of Transportation that you will be held financially responsible for the repair of the guardrail damage. For example, in Florida whenever someone damages DOT property, whether it is guardrail, a vehicle, or a bridge, that person is responsible for paying for the damage. Payment can come from the driver or owner, or both, or their insurance companies.

Now normally insurance follows a vehicle first and driver second meaning that typically your liability insurance would pay and if your limits are exceeded then the friend's liability insurance would be used as excess. If you are charged for the repairs of the guardrail then you may want to check with your insurance provider as well as the driver's to see who will be primary in this case.