R17

R17 / 1:1

Shared Single Road Lane constrains traffic flowing in opposite directions on one Shared Road Segment

Shared Road Segment flows opposing traffic both ways in one Shared Single Road Lane

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When a road has a single lane, is there really a lane at all? The main purpose of lanes is to separate traffic via physical or marked boundaries. It is certainly the case that a Shared Road Segment might have markings or physical boundaries on the left or right. These are coincident with the Road Edges and Road Edges are defined by the extreme Lane Divisions.

So, yes, even the minimal case of a Shared Road Segment does require a Lane.

By definition, a Shared Single Road Lane must be laid out on a Shared Road Segment.

Formalization

Shared Single Road Lane.Road segment -> Shared Road Segment.ID