When during the meetings the Americans offered that at most they could convert 15 percent of U.S. auto plants to military production, Beaverbrook replies that 100 percent of British automobile factories had been converted, and encouraged Roosevelt to aim higher.  He did, and on January 1 he ordered U.S. auto production halted by late Februrary.  Within weeks the dearth of newe cars became moot when rubber, 90 percent of which came from Malaya and Indonesia, was rationed.  The U.S. had no synthetic rubber factories to make up the shortfall.  Americans soon learned what Britons had long known: without a spare tire or three stashed in the garage, the family car had a very limited range.  Passage by rail — where for fifty years the Pullmans had been Americans’ preferred means of conveyance — was soon limited to troops and businessmen on official war business.  And then the airlines — their routes and the national fleet of 434 aircraft — were commandeered.  By spring, gasoline ratioining, as a mean to preserve rubber more than oil, dribbed on to the Eastern Seaboard and in the following year spread nationwide, guaranteeing that west coast beaches even if their bald tires could carry them there.  That proved okay with most because by summer, oil and bilge tar and decomposing bodies — the U-boats’ harvest — regularly washed up onto America’s eastern beaches.

That is all from the excellent The Last Lion: Winston Spencer Churchill: Defender of the Realm, 1940-1965.  As I’ve said before, you can always keep on reading books about World War II and you will continue to learn interesting and important things.