I've posted in the sibling thread r.e. the density (which I believe you have underestimated by several orders of magnitude), however a stroll around london will show you that, excepting arterial roads, cars always have to deal with pedestrians crossing at any time and place, including between you and the car ahead if you come to a stop, or if there's more than a couple meters between you and the next car. Even busy arterial roads will have to deal with people walking across them if there are large gaps or the traffic is slow or stalled.