How do you get a at fault accident changed to no fault? No guide rails on the shoulder of a 20 foot drop made from a culvert pipe - was clearly not drivers fault but is on the accident report as at fault. No markers of any danger. Is there anything that can be done?

For what purpose? Insurance? Did you get a ticket? Try to persuade them the accident report was wrong and that it was not your fault.

No ticket - just want to get this changed for insurance reasons and possible litigation from this in the future.

I am still unclear about what you mean by an "accident report".

If it is a police report, that is just one person's opinion. The insurance company, or whoever would adjudicate possible litigation, is free to second-guess it.

Yes, I've seen Police Accident Reports corrected if there are substantial errors or VERY strong witnesses are willing to give affidavits.

I have never seen one change simply for purposes of insurance.

The insurance investigator assigned to this accident will look beyond the Police Report (I see PRs with fairly substantial errors all the time) and come to his/her own conclusions.

I'm a little confused about why you think no one is at fault for this accident. Guardrails or no guardrails a person driving on the highway, between the fog line and the center line, would not go off the highway.