Plenty of recent talk about reaching 7B people ("crack out yer Soylent Green!"), but here's Bill Ford saying the number of cars in the world - just now reaching 1B - will quadruple to 4B by 2050.
No, there won't be enough oil for all that transpo, or - more truthfully - we won't want to go to that effort.
So the age of post-gas-combustion awaits. Ultimat driver is oil availability, but proximate driver is local air pollution.