If your mileage is great on the highway and terrible in the city, you are not imagining it. City vs highway mileage can swing hard because the engine works differently in stop-and-go driving. Once you understand the mechanics, the numbers make sense.
Acceleration is expensive. Cruising is cheap. City driving is mostly acceleration, while highway driving is mostly steady speed.
1. Acceleration Burns the Most Fuel
Every time you stop and go, the engine dumps extra fuel to overcome inertia. That is why stop and go fuel economy is always worse. In the city, you repeat that cycle dozens of times each trip.
2. Idling Adds Zero Miles
Idling still burns fuel, but you are not moving. That drags your average down. In traffic, idling can consume a surprising amount of a tank without adding distance.
3. Highway Speed is Predictable
At a steady speed, the engine runs in a more efficient range. That is why highway fuel efficiency is usually higher. You are spending more time in top gear with fewer throttle changes.
4. Speed Has a Hidden Penalty
Highway fuel efficiency is best at moderate speed. Past a certain point, wind resistance rises fast. If you drive 75-80 instead of 60-65, you can lose a lot of mileage even on the highway.
Steady speed beats high speed. Smooth inputs beat aggressive ones.
5. Compare the Right Way
- Use full tanks. One short trip can mislead you.
- Separate trip types. Track city and highway tanks separately.
- Ignore one-off days. Look at a few weeks of data.
Why Your Mileage Swings Are Normal
City vs highway mileage will always swing because the engine works hardest in stop-and-go conditions. The fix is not to panic. It is to separate your trips and track them consistently.
Once you do that, your fuel economy drop stops being a mystery and starts being predictable.