Dear Umbra, I was babbling about the '70s energy crisis, gas rationing, and the nationwide 55 mile-per-hour speed limit at work the other day, and found myself explaining to a group of younger people how you save gas if you drive slower. They had never heard such a thing! Could you refresh my memory about why 55 is the magic number for saving fuel? They need to hear it in scientificese. RuthDenton, Texas Dearest Ruth, As you well remember, 55 mph was decreed the national speed limit in 1973. It was lifted in rural areas in 1987, but stuck around …
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