They're called airdams here Down Under too. I imagine they'd have
little if any aerodynamic effect on our buses.

I wouldn't mind one, but I do go up 4WD tracks, and stream crossings
etc would soon scrape it off. Also Dunedin is full of deep gutters at
driveway entrances, and these would do likewise (I had a steel
bullbar on my Bay, 2 tubes ran forward right up against the bottom of
the bumper, and banged this hard on some entrances).