City vs. Highway MPG: Why the Same Car Gets Different Mileage
City driving generally produces lower fuel economy due to frequent stopping and starting, idling in traffic, and driving at lower, less fuel-efficient speeds — highway driving generally produces higher fuel economy through sustained, steady speeds in an efficient range, though very high highway speeds eventually reduce efficiency again due to increased aerodynamic drag.
This is one of the most consistently observed patterns in vehicle fuel economy, driven by real, identifiable mechanical and aerodynamic factors.
Why city driving reduces fuel economy
Frequent acceleration from a stop consumes disproportionately more fuel than maintaining a steady speed, and idling while stopped in traffic burns fuel while covering zero distance — both effects are much more common in city driving than highway driving, which is why city fuel economy ratings are consistently lower than highway ratings for the same vehicle.
Why highway driving generally improves fuel economy
Sustained, steady-speed highway driving in a vehicle's efficient speed range avoids the repeated acceleration and idling losses that dominate city driving — most vehicles have a "sweet spot" speed range (commonly somewhere in the 45-65 mph range) where fuel economy peaks.
Why very high speeds reduce efficiency again
Beyond a vehicle's efficient speed range, aerodynamic drag increases significantly with speed (drag increases roughly with the square of speed), which is why fuel economy actually declines again at very high highway speeds despite the steady-speed advantage — there's a genuine efficiency peak, not a simple "faster highway driving is always more efficient" relationship.