Like everyone has said, there are no standards in many places. Our solution in such places (LOTS of areas in West Virginia, and some in Tennessee) is to detach the toad, and send DW out in front with her cell phone. In areas of no cell service, we have a set of small radios. She can tell me of any problem areas coming up, and if there is any traffic coming toward me. That way I know that I can safely take blind curves and whatever, knowing that is is clear on the other side. Also she can warn me of any low underpasses or narrow bridges beforehand, and hopefully find a place to turn around if necessary. As far as major highways or interstates, High flyovers with low sides have only one lane. And it usually has a white line right down the center!