You obviously haven't driven on the madmax style roads in the u.s. There's no etiquette, it's every man for himself out there and you have to drive defensively. If you get over just to let one of those drivers pass you, they'll just cut you off so they can weave between lanes or cut across 5 lanes to take an exit. There's no winning in these situations. If you're passing other cars, then there's no reason to get back over to let faster cars pass you unless the road is wide open.