Originally Posted by Helmet Head
I can't imagine a road with a margin of zero width - that would mean that cars are regularly driven rubbing up against the curb or driven with the tires at the edge of the pavement and unpaved shoulder.
These roads exist. Especially way out in the country. I grew up driving on roads that were not big enough for two cars to pass going opposite directions. One would have to pull off onto the grass or what-have-you and wait for the other car to go by.
Of course, out in the country people are friendly and this happens without a second thought.