2-7kg personal vehicles are optimal efficiency, 20-70kg personal vehicles allow for everyone to do anything (okay some of the larger electric wheelchairs blow past 70kg pretty easily, but allow me some artistic licence).
Even busses aren't amazing on vehicle weight per person: 16,000kg for 50 people is 320kg per person. Good suburban trains bring that back down to 230kg per person.
So for cars to be viable your 5 seater needs to be 1600kg max. And one needs to actually use those seats.