You guys are right, it was Nixon. Maxima Mea Culpa. I plead old age.
I was overseas when it happened, and have no excuse for not remembering the Nixon years... and the bombing of Hanoi (that's why I was overseas). I guess the 55mph speed limit impact on me was just plain overwhelmed by the bombing of Hanoi (Operation Linebacker II), the 15 B-52s we lost in the Operation, Ho coming to the table as a result of the operation, and all the other much more important stuff going on at the time. This forum not being a military history forum, I'll just admit my memory error and get back to cars. I'm truly sorry I got distracted.
The 55 mph limits may have reduced fuel usage some, which was their intent, but unfortunately the effect on safety was that it created greater differences in the speeds of the cars sharing the highways, as well as early versions of "road rage", and subsequently reduced safety. Speed differences on highways cause flow turbulence, and that causes accidents, especially at night. Especially when a line of drivers headed home after a long day's work gets bunched up on a highway designed for 70mph behind some guy doing 55 mph. It's true that accident damages rise with speed, but the number of accidents rises with obstructions. And "rolling bottlenecks" are obstructions.