Well, it just might be that whether it is commercial trucks or people with their cars at the dump, people can accurately perceive that there is an open and obvious hazard present which they are voluntarially choosing to confront. Knowing that they are facing an obvious hazard normal people look out for their own safety. Folks seem to have been doing this successfully at the dump for decades.  If they fail to look out for their own safety under the circumstances, it is they, not the county, that are negligent. 

Any trial lawyer worth his/her salt would have a field day defending the county. I can hear it now: "Tell the jury again Mr. Plaintiff, how it is you failed to see this enormous pit that you fell into?" "Then tell them again when they quit laughing."