The number of riders who will share a vehicle is a key unknown. In the U.S., the average car carries 1.16 persons, and most industrialized countries commonly average below two people; not having to share a vehicle with strangers is a key advantage of private transport. Based on these figures, some have suggested that two passengers per vehicle (such as with UniModal), or even a single passenger per vehicle is optimum. Other designs use a car for a model, and choose larger vehicles, making it possible to accommodate families with small children, riders with bicycles, disabled passengers with wheelchairs, or a pallet or two of freight.