Err...motorists aren't always the problem, sometimes it's the very authority that's responsible for cleaning it up.
We were driving the A1 sometime last year near Newark. There was a council refuse lorry driving along...spewing rubbish and litter out the open back.
In that moment I thought I'm going to phone them later....but later, I couldn't remember what authority it was, etc etc...and so I shrugged my shoulders and moved on.