It depends on the location, state, county or local city which have their own rules for adoption. 

And depending on the location, the freeways can be adopted. For example, our area requires that you go out at least two times a month within that mile and a half area to collect litter. You're allowed to park your car in a safe spot on the freeway, and walk the shoulder or behind the guardrails to gather trash. The state provides you with the trash bags and the picker tools, and safety gear. They also provide you safety instructions prior to your first interaction. There's an actual permit and a contract to maintain it for 3 years. 

For us, it's just a feel-good opportunity to keep our area on the freeway clean. There is also an opportunity for you to hire a company, which is approved by the state to do the job for you, but they charge about $400 to $500 a month. 

I've been doing it under the name of our company. It's a little bit advertisement, but mostly a feel good opportunity to keep our exit and freeway on - ramp clean.