When using the A/C in the city you will get less fuel mileage than with the windows down. However using the A/C on the highway will give you better fuel mileage than driving with the windows down. Reason being is that with the windows open this is creating a drag on the car. The drag from windows down at highway speed is greater than the drag from the compressor. The compressors used in cars today do not put near the drag on an engine as the one's used a decade ago. On the highway use the A/C and in town turn it off and roll the windows down. This will give you the best fuel mileage. Now, with a large SUV or Pickup this is not true. Running with the windows down is always better due to the fact that a large SUV and Pickup already have a huge drag and the windows down really makes no difference at all. On a Large SUV or Pickup running with the A/C off is always more fuel efficient.

Any vehicle will use more fuel while driving in town and with the air on. The constant stopping and going alone will use more fuel and when you add the air, it will use a little more fuel. When you are driving out on the freeways, you are maintaining your speed more and you will get better fuel mileage even with the air on. The vehicle will still use a bit more fuel with the air on, but it won't be very noticeable. Cruise control is on a vehicle to help maintain a constant speed, thus saving you fuel, and you don't have to have your foot on the gas pedal either. Sometimes some vehicles will over heat when driving in town with the air on. Reason being, they are not going fast enough and long enough to cool the coolant back down.

The short answer is yes, stop and go traffic will always result in less mileage unless you drive a hybrid. Adding the A/C to the equation makes the gas go even quicker. Hiway driving is more fuel efficient because your normally at a constant speed, not accelerating and braking all the time. and even with the A/C on, it will not impact the mileage as much, though it will still decrease the mileage significantly.

Town driving is worse on fuel economy with the air conditioner on than high constant speed driving.

i know enough about cars to get me through. some things i can do myself and i know which cars i like and why. i moved to FL and got into a conversation with my grandparents. i try not to use my AC unless i really need to, to save on gas. My grandparents do a lot of cross country driving and i told them i dont use my air much bc it drains my gas. my grandfather said it shouldnt matter much but it does. i do a lot of in town driving. i have a 2010 lancer. will using your AC in town make your gas go down faster than when your driving long distances like cross country?