U.S. national average passenger car "fuel economy" is about 25 miles per gallon. Current Federal legislation mandates the national standard fuel=economy of 54 miles per gallon (mpg)by 2025.
Political rhetoric touts this as the doubling of "fuel-economy." Doubling is same as the 100% improvement. (54 mpg - 25 mpg)/25 mpg = about 1, which is 100%.
With this change in national fuel-economy standard, find percent increase in "energy efficiency?"