Passing on a 2 lane highway. If it's straight and flat, and you're behind a big square boxy truck, you just can't see. You either sit behind slow poke, wait for a bend in the road which enables you to see past the slow vehicle, or, if you have a passenger who's judgement you REALLY trust, they can advise you on the passability of the oncoming traffic. The only remaining option is to pull WAY out into the oncoming traffic lane to see around him.
The other option is to move over to the right a bit and look up that side.
Good to have your comments. Anyone else?