Regarding litter on our roads, my wife and I rarely see trash thrown out of car windows. Garbage trucks are a different story. We have seen these trucks traveling our highways overloaded or with unsecured loads leaving a trail of litter in their wake.
On our neighborhood they pack down their load with a good shake of the loading bin, usually leaving a little trash on the roadside as a memento. The trash on the approach to transfer stations appears to be blow-offs from commercial trucks since most people bag their individual loads.
So maybe the cost of cleanup should be paid more in part by the commercial haulers. Better yet, they should train their employees to get out and look their loads over for loose items before taking off down the road. We would not have as much litter to clean up in that case.