Large cars were out. Aside from making numerous expensive changes to cars to improve their gasoline efficiency, the only alternative for manufacturers was to sell smaller cars. The average fuel consumption of automobiles depends partly upon what cars are on the road, and how far they are driven annually. For example, if everybody owned a 1970 Cadillac, the average car might get 12 miles per gallon, but if everybody owned a 1956 Volkswagen beetle, the average car would get about 30 miles per gallon. If half owned the Caddies and half the beetles, the average mileage would be 21 miles per gallon, providing that all cars went the same distance every year.
CAFE assumes equal driving for all vehicles.
Manufacturers were required to sell small cars, and to discourage the purchase of large cars. At the time CAFE was introduced, one of the most popular cars was the station wagon. They were so popular that it would be impossible to meet CAFE standards if station wagons continued to be sold at the then current rates. There were other effects as well, not least of which was the escalation of anti-nuclear rhetoric. To this day, decades after the OPEC embargo, the Department Opposed to Energy waxes eloquent about efficiency and expensive, ineffectual, solar toys.