I must confess I have never heard of a collection box for hedge cutters. As I understand it, the cutting of road side hedges is actually the responsibility of the council, although farmers often get lumbered with the job as they have the gear to do it and councils can illafford to splash out new hedge cutting equipment. So maybe a little word with your local councelor would be five minutes well spent.
There seems to be this opinion going around that when a farmer does something that someone else doesn't much appreciate, they have done it just to annoy the general pubilc. Case in point, when the farmer trims the hedges on the roads, he does so at the behest of local government to allow the free passage of Tax Paying road vehicles. At present there isn't the technology to collect the trimmings so when they fall on the floor, it's isn't a meliscious act on the part of the driver, it's just that there is no where else for them to go. Some councils do have their own hedge cutting equipment which does exactly the same thing as farm owned trimmers. Perhaps the council could come along and sweep the roads after??
"Dogs look up to us, cats look down on us, but pigs treat us as equals." (Sir Winston Churchill)