The majority of the roads that aren't highways do not have lanes. The road layout is largely from a hundred or two years before cars existed.

I fail to see the relevance of this comment?

>>> Those seems like situations where extra spacing will help accomodated unexpeded mergings and lane changes without slowing traffic down.

>> The majority of the roads that aren't highways do not have lanes.

> I fail to see the relevance of this comment?

... you don't see how roads lacking lanes applies to the efficiency of merges and lane changes?

So the point you were trying to make is that single land roads don't face traffic issues from merges and lane changes? That seems to trivially be false in my experience. Having driving all over the USA on roads with a single lane in each direction, merges and lane changes are by far the biggest cause of traffic slow downs.

Sure thing, bud.