The driving factor was clean air legislation generally, which mandated the use of catalytic converters in new cars. Lead poisons the catalyst; a tank of leaded

The driving factor was clean air legislation generally, which mandated the use of catalytic converters in new cars. Lead poisons the catalyst; a tank of leaded gasoline would be plenty to render a catalytic converter useless. Eliminating atmospheric lead may have been a consideration, but in my recollection it wasn't the primary consideration; people were more concerned about unburned hydrocarbons producing smog.