I think they are going to have to get out and physically walk up and down those roads. Moving no faster than walking speed will allow them to see things much more clearly than driving along in a vehicle.
I know it is easy to sit here in the comfort of my air conditioned home with a can of beer in one hand and a laptop mouse in the other, and make such suggestions. We all know how these searches go sometimes though, with the searchers claiming they have "exhaustively searched" a certain area, and then a month or two later the person is found by a jogger or somebody out walking their dog dead smack in the middle of the search zone that was "previously searched."
Luckily in this case, they are looking for a large object that reflects sunlight and is much easier to spot, but it could still be either partially or almost completely concealed from view. Walking along at a snails pace and getting way over on the shoulder will allow them to see and notice things that normally wouldn't be seen. I've walked along the side of roads before and it's amazing all the junk you see littered around down in the bar ditches. Beer cans, baby diapers, tow straps, water bottles, car parts, tires, etc......normally you never notice this stuff when zipping along at highway speed.
Using bicycles instead of walking might be another good option, but it would force one to stay on the pavement rather than get way over past the shoulder. It is a hazardous process either way because of the rude motorists that seem to think they are required to drive like bats out of hell no matter where they are heading.
