Common on both scenario, the engine is consuming fuel

City Driving:
1. Engine is burning fuel
2. Due to traffic, most of the fuel is burned while not moving, hence no mileage to show
3. Engine use more fuel if on low gear,
3.1. imagine yourself using bicycle, from stop to move it takes you more effort to pedal as your gear is set to the lowest.


Hi-way driving:
1. Engine is burning fuel
2. as the fuel is burned, it is directly converted into mileage
3. as the car is already moving, and already in mid to high gear,
3.2. imagine yourself using a bicycle, but you are already moving, it takes less effort to pedal as you are only adding force to sustain the speed.