If you’ve paid attention to your car’s EPA fuel economy estimates, odds are you’ve noticed that a car’s city MPG rating is usually worse than its highway MPG rating. I say “usually,” because some gasoline-electric hybrids get better gas mileage in the city than they do on the highway, but that’s pretty much the only exception when it comes to vehicles that rely on internal combustion. It’s true that most cars return worse gas mileage during stop-and-go city driving than they do when driving on wide open highways, but why is that?
Of course, it all comes down to physics — Newton’s First Law of Motion states that an object in motion stays in motion. I never took physics in school, so I’m not going deeper into the actual science than that, but it just boils down to how much energy it takes to move your car. If you’ve ever had to push a car, you know that the first few inches of movement takes far more energy than it takes for you to simply keep the car rolling, right? It’s all about energy transfer. Here’s what I mean.
Repeated stopping and going takes a lot of energy
In a city, you’re going to encounter lots of busy intersections with red lights, stop signs, and pedestrian crossings that require you to stop. Every time you stop, you have to get moving again, which takes a lot of energy.
When you pull away from a stop, your engine RPMs increase, which generally means your car is using more fuel. Whether your car has a CVT, a traditional automatic transmission, or a manual transmission, internal combustion engines need to be operating at higher RPMs in order to produce the power that is needed to get a car moving. Especially in gasoline-powered vehicles, engines make more power, and thus require more fuel, as the engine speed rises.
When you drive on the highway, your engine usually sits at a relatively consistent, low RPM. This is because your vehicle is already in motion, and it requires less energy (gas) to keep it traveling at that speed. An object in motion stays in motion! As speeds rise, you use less gas to travel farther distances, until the aerodynamic drag on your vehicle becomes too great and your engine has to work harder to keep your car piercing through the air.
How to maximize your fuel efficiency
Consistency is key to achieving great fuel economy; if you keep your car’s engine working at a sensible and consistent speed, most engines sip fuel. In order to maximize your car’s fuel economy and thus minimize your fuel consumption, you want to avoid lots of stopping and starting again.
Look farther down the road to be able to predict when you need to slow down, so you can coast and gradually decelerate rather than keeping your foot on the gas pedal and then slamming on the brakes at the last minute. When you stay on the gas for too long and have to slam on the brakes, it means you could have saved fuel if you decelerated more gradually.
When you accelerate, whether it’s from a stop at a red light or getting up to highway speeds, you want to keep your engine speeds low, so don’t accelerate more aggressively than you need to. Of course, you don’t want to become a hazard on the road by driving or accelerating too slowly so always mind the flow of traffic, but accelerating sensibly will help you get the most out of every gallon of gas.
