Enforced garbage collection

Whilst driving down the highway it is not uncommon to see this sign - "Caution: Prison inmates working ahead" And then a few minutes later you see a dozen or so men dressed in bright orange vests picking up garbage from the roadside and putting it in bags. The NC Department of Correction's website states that "Today's N.C. prison inmates work on the farm, on road crews and in prison construction. More than 2,000 minimum and medium custody inmates from more than 60 prisons work on the state's roads, clearing right-of-way, picking up litter and patching potholes. Medium custody inmates work under the supervision of armed correctional officers. Minimum custody inmates work under the direction of Department of Transportation employees." One thing I can say is that the highways in NC are incredibly clean and in our recent travels we did not see any litter lying around. I guess there must be a lot of prisoners to do the work.