mdbarb--
This got long-winded, so feel free to quit now, but I've done this a few times both as somebody with a beef and as a mediator and might be able to get you a little bit comfortable with the process.
I assume your lawyer has told you that mediation typically involves a setting where everybody starts out in one room, usually for a relatively short time, followed by "shuttle diplomacy" periods where the mediator goes back and forth between separated parties. The mediation discussions are privileged settlement talks. A good mediator will advise you that anything said outside the presence of the other side is confidential and will not be repeated without your permission, and will obtain permission on a point-by-point basis to shuttle an argument, offer, or response to the other side.
A few points. First, as to the nature of mediation. Its sole purpose is to try to bring parties to agreement. Mediators do not decide issues or make decisions. They bring not-very-willing buyers together with not-very-willing sellers and try to broker a deal. They may reason, argue, cajole, and if it is a bad mediator beg or bully, but they cannot decide.
Second. Mediation does not work when a dispute is completely one-sided, or when one party's expecatations or demands are unreasonable. Here, the issues are tiny in the scheme of things, but huge to you--and presumably to your neighbor. On the other hand, your neighbor does, sadly under the circumstances, have a legal right to use a portion of your property for certain things. Thus, the dispute is, IMO, not completely one-sided, meaning that your goal should be to constrain the process toward a mangeable goal, for example no lateral expansion of the roadway and no use of the land beyond the turn, as well as payment of at least a portion of your fees. This is a position which will be wholly untenable to your neighbor, but may grab the mediator's attention, as well as that of opposing counsel.
Fourth. (what hapened to third? I have no idea.) Mediators thrive on information they can deploy against the other side at strategic moments. If the mediator is not familiar with the case, make sure that your lawyer, or if necessary you, make her aware that the judge has been pounding on your adversary, and describe the scene out at the house when the judge came out for the view, as well as the recusal accusations.
Fifth. Prepare for mediation like a trial. Be ready to discuss every point of your case. Spend time with your lawyer, and make sure he knows you are taking the process seriously.
Third (there it is--I knew it was somewhere.) Bring PICTURES. 24x36 if possible; at least 11x14. Maybe one big and a bunch of little ones. But that thousand-words thing is, of course, for real.
Fifth (or whatever). Mediators are often dramatically far from prescient. I had a mediator in San Francisco try to bully our team into a $14MM settlement a few years ago on a case against Boeing that settled for $61MM. Don't be afraid to walk away if the mediator is full of it: Just be sure that before you do so, you have carefully considered her points and that disagreement is principled, rather than visceral. On the other hand, it is dramatically better to have your opponent, rather than you, declare an impasse.
Don't be afraid to compromise, so long as the compromise is legitimate. That is, don't take a deal just because it's there, but don't be self-righteous. Remember, once again, that sad but true, you have to live next door to this character indefinitely.
Don't be afraid to suggest outlandish possibilities. Maybe your neighbor wants to sell his land; if you are interested, maybe your list of options should including suggesting a buyout. Brainstorm before you go in to see if there's anything that might float all boats.
Be open to the possibility, however incredibly remote, that you might be able to craft a win-win solution. Remember that, sad but true, you have to live next door to this character indefinitely. At a minimum, I would do my best to signal to the mediator that while you have been severely abused in this situation, you are willing to try a fresh start; again, let (make) your opponent be the heavy.
Finally. DO NOT agree to anything just to be done with it. Neighbor disputes have to either have stakes driven through their hearts or comprehensive agreements worked out. It sounds to me like you are on the road to the former, but are open to the latter if possible. Do not confuse resolution with surrender.
I always go into a mediation assuming that there will be two benefits. The first is that I will learn something about what the other side is thinking. The second is that I will learn what a neutral third party thinks about the situation. I am always open to the possibility of settlement, but I always assume that it will not occur.
Good luck!!