Why Your Car Gives 22 km/l on the Highway and 12 in the City

The same car, the same fuel, the same driver — and a 60-80% swing in fuel economy. Here is where the difference comes from.

Braking is the enemy

Fuel does one thing: it accelerates mass. Every time you brake, that energy leaves as heat through the pads and is gone forever. A highway drive might involve ten braking events in 100 km. A city commute involves several hundred. This is the single biggest factor, and it is why hybrids — which recover some of that energy — close the gap so dramatically.

Idling produces zero kilometres per litre

At a red light your engine is consuming roughly 0.6-1.0 litres per hour and covering no distance at all. In a commute that is 40% stationary, that alone can account for 10-15% of your fuel.

Engines are inefficient at low load

A petrol engine's best brake-specific fuel consumption occurs at moderate-to-high load and around 2,000-2,500 rpm. City driving keeps the throttle barely open, where pumping losses dominate and thermal efficiency can fall below 20%. On the highway at a steady 80 km/h in top gear, the same engine may run at 30-33% efficiency.

Cold starts

Until the coolant reaches operating temperature, the ECU runs a richer mixture and the oil is thick. The first 5-10 minutes of any drive can consume 30-50% more fuel per kilometre. City trips are short, so a larger fraction of every trip is spent cold.

Where the highway loses

Aerodynamic drag rises with the square of speed and power demand with the cube. That is why highway economy peaks around 70-90 km/h and falls off sharply after 110 km/h. Driving at 130 km/h can be less efficient than crawling through traffic in a small car.

Narrowing the gap

• Look far ahead and coast to lights instead of braking
• Combine short trips so the engine is warm for more of the distance
• Switch off at signals longer than 30 seconds, or leave idle start-stop enabled
• Pick routes with fewer signals even if they are slightly longer
• On the highway, hold 80-90 km/h rather than surging between 70 and 120

Realistically, a disciplined driver narrows a 12 vs 22 km/l gap to something like 15 vs 21. That is worth roughly ₹1,500 a month on a typical commute.