Sentence:  But in 1982 they found a loophole: Keep the <WSD>double-nickel</WSD> speed limit, but effectively allow motorists to drive up to 65 by designating that speed a “waste of a finite resource” and setting the fine at $15. 
Meaning of the word marked with <WSD> tags:  The national speed limit of 55 miles per hour introduced in the USA in 1974.