Why Your Car Uses More Gas on the Highway Than in the City

Highway fuel economy is almost always better than city fuel economy, but the difference surprises most drivers

Your car's fuel economy rating comes in two numbers: highway and city. The highway number is higher — sometimes much higher — because highway driving is mechanically simpler. On the highway, your engine runs at a steady speed in a high gear, burning fuel efficiently. In the city, you stop and start constantly, shift gears repeatedly, and idle at red lights. That constant acceleration and braking wastes fuel even though you are covering fewer miles per hour.

The gap between the two numbers matters when you are planning a trip or comparing cars. A vehicle rated at 25 mpg city and 35 mpg highway will cost you more to drive around town than the sticker suggests. If you mostly drive locally, the city number is what your actual fuel bill will look like. If you mostly drive long distances, you will see fuel economy closer to the highway rating.

Key Takeaways

• Highway driving burns less fuel per mile because your engine runs at a steady speed without stopping, idling, or shifting gears.
• City driving wastes fuel through constant acceleration, braking, and idling at traffic lights, even though you are traveling at lower speeds.
• The EPA rates every car with both numbers so you can estimate fuel costs based on how you actually drive.
• Your real-world fuel economy will fall somewhere between the two ratings depending on your mix of highway and city miles.
• Hybrid and electric vehicles show an even larger gap between city and highway because regenerative braking recovers energy in stop-and-go traffic.

Why the highway number is always higher

On the highway, your engine reaches an optimal operating point. You accelerate to cruising speed — usually 55 to 75 mph — shift into a high gear, and maintain that speed for miles. Your engine burns fuel at a steady rate with minimal waste. There is no idling, no downshifting, no sudden acceleration. The transmission stays in one gear, and the engine does not have to work harder or softer every few seconds.

City driving is the opposite. You accelerate from a stop, brake for a red light, idle while waiting, accelerate again. Each acceleration burns extra fuel because the engine has to produce sudden power. Braking wastes the energy you just spent accelerating — that kinetic energy becomes heat in your brake pads instead of moving you forward. Idling burns fuel while you cover zero miles. Over a typical city drive, you might accelerate and brake 20 or 30 times in a few miles.

The speed itself is not the main factor. A car driven at a constant 35 mph on a long straight road will have better fuel economy than the same car driven at 35 mph in the city, because the city version includes all those stops and starts. The EPA's city test actually includes some highway-speed driving — it is called the city test because it simulates city driving patterns, not because the speed is low.

How the EPA measures each rating

The EPA tests every new car on a dynamometer — a machine that simulates driving without the car actually moving. The city test lasts about 23 minutes and covers a simulated 5.8 miles. The car accelerates and brakes repeatedly, idles at simulated traffic lights, and reaches a top speed of 56 mph. The highway test lasts about 20 minutes, covers 10.3 miles, and keeps the car at steady speeds between 48 and 60 mph with minimal braking.

These tests produce two separate numbers. The EPA then adjusts both downward by about 15 percent to account for the fact that real-world driving is less efficient than laboratory conditions. Even with that adjustment, the highway number stays higher because the test itself reflects the mechanical reality: steady-speed driving uses less fuel than stop-and-go driving.

The EPA also publishes a combined rating, which is a weighted average of the two. The combined number weights city driving more heavily because most people drive in the city more often than on the highway. If a car is rated 25 city, 35 highway, the combined rating might be 29 mpg — closer to the city number because that is where most of your miles happen.

What your actual fuel economy will be

Your real fuel economy depends on how you drive. If you drive 80 percent city and 20 percent highway, your actual mpg will be much closer to the city rating. If you drive 20 percent city and 80 percent highway, you will see fuel economy close to the highway rating. Most drivers fall somewhere in between, so the combined rating is a reasonable estimate for planning purposes.

Several factors can push your actual economy above or below the EPA ratings. Driving at highway speeds above 60 mph burns more fuel than the test assumes. Idling in traffic, using air conditioning, and carrying heavy cargo all reduce fuel economy. Conversely, gentle acceleration, steady speeds, and well-maintained tires can improve it. Cold weather also reduces fuel economy because the engine needs more fuel to warm up and oil is thicker in cold temperatures.

You can track your actual fuel economy by dividing the miles you drove by the gallons you pumped. Do this over several fill-ups to get an accurate picture. Most modern cars also display fuel economy on the dashboard, though that number can be optimistic compared to the math you do yourself.

The gap is wider in hybrid and electric vehicles

Hybrid cars show an even larger difference between city and highway ratings because they recover energy during braking. When you brake in a hybrid, the electric motor captures that kinetic energy and stores it in the battery instead of wasting it as heat. In the city, where you brake constantly, the hybrid recovers a lot of energy. On the highway, where you brake rarely, there is little energy to recover. A hybrid rated 50 mpg city and 45 mpg highway is not unusual.

Electric vehicles show the opposite pattern. They are rated in miles per gallon equivalent (MPGe), which measures how far they travel on the energy in a gallon of gasoline. City driving in an EV is efficient because regenerative braking recovers energy. But highway driving at high speeds drains the battery faster because aerodynamic drag increases with speed. An EV rated 130 MPGe city and 100 MPGe highway reflects this reality.

How fuel economy affects your trip costs

When you plan a long trip, use the highway rating to estimate fuel costs. When you budget for regular driving, use the combined or city rating. If you are comparing two cars and one gets 25 city and 35 highway while the other gets 28 city and 32 highway, the second car is probably better for city driving even though the highway number is lower.

The EPA label on every new car shows both numbers prominently, along with an estimate of annual fuel cost based on 15,000 miles per year split between city and highway driving. That estimate assumes national average gas prices, so your actual cost will vary. But the label gives you a way to compare the fuel costs of different vehicles side by side.

Frequently Asked Questions

Why does my car get worse fuel economy than the EPA rating says?

The EPA rating assumes moderate driving with no traffic jams, cold starts, or highway speeds above 60 mph. Real-world driving usually includes at least some of these. Idling in traffic, frequent acceleration, and driving faster than 65 mph all reduce fuel economy. Cold weather and a heavy load also lower it. Track your actual mpg over several fill-ups to see where you stand.

Does driving at 55 mph instead of 70 mph really save that much gas?

Yes. Fuel economy drops noticeably above 60 mph because aerodynamic drag increases with speed. Driving at 55 instead of 70 can improve highway fuel economy by 10 to 15 percent. However, the time cost of driving slower may outweigh the fuel savings for most trips. The math depends on gas prices and how much your time is worth to you.

Is the combined rating the same as my actual fuel economy?

The combined rating is a reasonable estimate if your driving mix matches the EPA's assumption — about 55 percent city and 45 percent highway. If you drive mostly city or mostly highway, your actual economy will be closer to whichever rating matches your pattern. Track your own mpg to know for certain.

Do all cars have better highway fuel economy than city?

Almost all gasoline and diesel cars do. The only exceptions are some very large trucks and SUVs where aerodynamic drag at highway speeds becomes significant enough to offset the efficiency gains of steady-speed driving. Even then, the difference is usually small. Hybrids and electric vehicles can show different patterns because of how they recover braking energy.