[prawn]

Are you referencing that Idaho scenario? This generally assumes the shoulder is long enough, that the car behind you can see it and realise that's what's happening, that there is visibility, etc. From memory, in that Idaho (?) case while the visibility was good and it was generally a straight road, the shoulder was full of debris and unmaintained bushes. Also the shoulder is often a puncture risk.

Here in Australia, the road trains will often signal when it's safe for you to overtake them - they're seated higher with better visibility, have far better lights for night driving, etc. But I always hear that their employers/industry discourage them from doing this, I assume out of fear of liability.

I've driven x0k miles in the US and tried signalling like this when I can tell someone desperately wants to overtake me ("go now, it's clear ahead"), but almost no one understands the intention.

IMO, most RV/truck/etc drivers dislike holding up traffic as much as the traffic dislikes being held up!