You're probably SOL.
Several years ago, I came over a rise on an unfamiliar road and hit a significant pothole which sent be over the handlebars and into the ER. Not having any insurance at the time, I sought legal advice and was told that municipalities are protected against litigation.
Your state might be different and it doesn't hurt to seek legal advice. I was dealing with a few thousand dollars worth of medical bills and it made no difference at all.