The cover of the May 1956 issue of Chilton's Motor Age touted its "prediction of the automotive future." What could it have been? I went ahead and bought a copy.
In short, they were both right and wrong.
Based on a variety of factors, including the rise of multiple car ownership, the car replacement market, and the population boom (especially in surburbia), the magazine's engineering editor suggested, rather optimistically, that by 1975 annual automobile production [note: in the U.S.] would perhaps reach 8,330,000 cars (10 million, including commercial vehicles).
In fact, 6,717,000 automobiles were produced in the U.S. in 1975 (8,987,000, including commercial), according to the American Automobile Manufacturers Association.
More interesting, at least to me, is the fact we didn't come close to reaching Chilton's forecasted figure until 1985, when the U.S. produced 8,185,000 cars. Furthermore, this actually represented the peak of passenger automobile production in the U.S. By 1995, the number had dropped back down to 6,350,000.*
Update: I missed the AAMA's data from 1965, which shows Chilton's prediction coming true a full decade earlier: 9,335,000 passenger, 1,803,000 commercial vehicles. By 1970, though, the figure had dropped dramatically &mdash i.e. the numbers in 1975 aren't close to what Chilton forecasted they'd be. For the next 20 years, too, production stayed below Chilton's prediction, apart from 1985.
What to make of all this: 1) forecasting should always be taken with a grain of salt (duh), and 2) the 1950s were the dawn of nuclear power, plastics, vaccines and antibiotics, and the space program. It must have been difficult not to get swept away by the sentiment that we'd be producing more of everything, and that that everything would only get better, more efficient and cheaper. Truth be told, I do agree with the last part.
*It's worth noting production of commercial vehicles increased more or less steadily year over year from 1980 to 1995.