A very random thought
You know, they always say "you're more likely to be murdered by someone you know than by a stranger". Which got me to thinking: would people also be more likely to be hit by a car by someone they know than pure random chance would have it? Since people tend to congregate in certain areas - near work, near their house - and the people they know probably tend to cluster in similar geographic areas, the probability - however minute - of people knowing the *#@! who hit them is probably increased.