A tandem bike with a trailer is a long piece of gear, longer than most drivers are used to dealing with. You've heard of those accidents involving a semi hauling double boxes, and as they're passing, some impatient fool in a car pulls left behind the first box.

If you were to create/find such a thing, I would make sure that there is some kind of visual warning that you have a "long load".

And I have absolutely no idea what it would be. Maybe a row of those triangular car-lot flags from high point in front to high point in back???

Sue