If the goal was MPG, then a civilian car should have no more than 80hp. You dont need more to get your hot pockets at Foodlion.. Do that and the goal would be met easily. Trucks, 300 hp, because they actually move the country....... Or just limit the speed limit back to 55, instant 25% fuel economy gain.
If the goal was to limit CO2 emissions, then HVAC systems should be outlawed, as heating, cooling and refrigeration is #1 in energy consumption in climates like the north or south.
What "can happen" 2-3 generations from now, always seems to be 2-3 generations away. Always.