A method and/or computer program product controls a physical spacing between self-driving vehicles (SDVs). One or more processors receive a social network node graph. The social network node graph describes a graphical distance between a first node on the social network node graph and a second node on the social network node graph. The first node represents a first passenger in a first SDV; the second node represents a second passenger in a second SDV; and the graphical distance between the first node and the second node describes a relationship level in a social network between the first passenger and the second passenger. An SDV on-board computer on at least one of the first SDV and the second SDV adjusts a physical spacing between the first SDV and the second SDV proportional to the graphical distance between the first node and the second node.