gas millage and EPA?

Question

why gas milliage from cars has to do with greenhouse gas emission or environment?

Answer 1

To say you get a certain amount of miles per gallon of gas is the same as saying you spend such-and-such an amount of money on gas per mile. The better mileage you receive, the less gas is used per mile, thus causing less emissions per mile.

This example cannot be used in the case of stop-still traffic.

Answer 2

In general, cars that get better mileage, produce less emissions per gallon of fuel burned than less fuel effificient cars. Not always true, but it's a good general rule.