slang The speed limit of 55 miles per hour. "Nickel" refers to the US five-cent coin. Whoa, whoa, cool it with the double nickels—the speed limit here is 25!
double nickelsand double buffalo
n. the number fifty-five; the fifty-five-mile-per-hour speed limit. (Originally citizens band radio. The buffalo is on one side of the nickel.) You’d better travel right on those double nickels in through here. The bears are hungry. Double buffalo is for trucks. You can go seventy.