Why gas consumption differs from highway to city
In: Engineering
City traffic is notoriously stop and go. For most cars, when you come to a complete stop your engine is still burning fuel but you’re not moving so its brutal on fuel economy. When you accelerate you burn a good deal of fuel to get moving, but then stopping again your brakes just take all that energy and turn it into heat to throw away.
Highways are more fuel efficient because you accelerate once (a lot of fuel for a bit) then cruise for a longgg time consuming a relatively low amount of fuel.
Highway speed is also more efficient for your engine than city speed. Your engine’s fuel consumption when cruising is its base fuel consumption + the fuel needed to overcome drag (rolling and air resistance). The base fuel consumption is always there regardless of the speed so traveling slowly results in poor fuel economy because even though drag is low your engine is burning a non-negligible amount of fuel just to keep spinning and your low speed doesn’t let you get many miles out of each gallon. As the speed picks up rolling resistance increases with speed and air resistance increases with speed^2 so there will be a point where things start getting worse, but modern cars are pretty good in the 55-75 range
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