because those 'zigs ziags' are called switch backs, and its easier to go left then right, then go straight up a mountain, because its most likely very steep. think about when you walk up a very steep...
Typically, uphill traffic has the right of way (Reference USFS driving). If driving in the mountains, one should be on the lookout for vehicles coming and wait at wide spots or pullouts for that...
the reason that roads "zigzag" while going up steep mountains is so that the incline is more gradual rather than being straight up. For example, if a mountain is 50 degrees up, that would be quite an...