The following is Valley's synopsis of the procedure of adopting a strech of highway. Valley is Wiccan so some of this may not apply to you but it's an excellent story and the information is invaluable.
From the Wisconsin Pagan Mailing List, Sun, 29 Aug 1999
Reprinted with Valley's permission:
I called my local Dept of Transportation, the number here is toll free, so yours probably would be too. This number is located in the 'government' section of the phone book.
The person who answers the phone here was very helpful and directed me to my new best friend, Don <gg>. He was slow to get our sign up, but very helpful about how to get started. I received a packet of information in the mail, picked out the name for our section of highway, and just followed the directions.
It took almost 9 months from the time of conception to the first time we 'hit the road'. So if anyone is thinking of cleaning up a section of highway in spring, I suggest you get started NOW. I picked up the "people working" sign, safety film (VCR tape), orange vests, garbage bags, and report cards (to let them know that someone was out there on site, and to report anything that we didn't pick up).
Next, I hit up my pagan friends, and begged a couple of local pagan groups to work. I did provide muffins, and drinks, but that is optional.
One only commits to three pick ups a year, and may back out at anytime. Just let the Dept know, so that another group may adopt your abandoned sight. Only drawback might be the organizer must give out an address. No problem for me, but I am SOOOOO out of the broom closet!
I guess a PO Box number would work just as well as a personal address, if this would be an issue for someone.
The good feelings far outweigh any work involved, but I do suggest a stretching out before beginning. I was very stiff the next morning.
Here is the proof of the above mentioned sign. Maria and Valley went out to do us a favor and snap some pictures of the sign, one very, very, foggy day: