Drive Slower, Save Money on Gas. Thanks, Physics!

Summer road trips are a lot of fun, but buying gas can feel painful when prices are high. The good news is that there is a simple, science-backed way to spend less money at the pump: slow down. Physics shows us that driving at a lower speed uses less fuel to cover the same distance, which means more money stays in your pocket.

You might think that speeding up would help you reach a gas station before you run out of fuel. Actually, the opposite is true. Driving slower means your car burns less gas per mile, so you can travel farther on what you have left. The physics behind this idea is easier to understand than you might expect.

Let's start with speed and time. Imagine you need to drive 30 miles on the highway, where the speed limit is 70 mph. At 70 mph, that trip takes about 25.7 minutes. If you push it to 75 mph, you arrive in about 24 minutes — saving only about 1.7 minutes, which is not a big deal for most trips.

Now here is the important part: going faster burns a lot more gas. When a car moves down the road, three forces act on it horizontally. The engine pushes the car forward, while rolling friction from the tires and air resistance — also called drag — push backward. The faster you drive, the harder those backward forces push against the car.

Air resistance is the key force to understand. It does not grow just a little when you speed up — it grows much faster than your speed does. If you double your speed, air drag becomes four times as strong. That means the engine has to work much harder and burn more gas just to maintain the higher pace.

The U.S. Department of Energy has studied this carefully. They found that for every 5 mph increase above 50 mph, fuel efficiency drops by about 7 percent. So if your car gets 30 miles per gallon at 70 mph, it only gets about 27.9 mpg at 75 mph. Slow down to 65 mph, and you would get about 32.3 mpg instead.

Now let's look at what this means for your wallet. On a 30-mile trip with gas at $4 per gallon, driving at 70 mph uses exactly 1 gallon and costs $4.00. Speed up to 75 mph and you use 1.08 gallons, adding 32 cents. Since you only saved 1.7 minutes, speeding cost you the equivalent of more than $11 for every hour you saved.

The savings get much bigger on a long trip. Picture a 500-mile round trip over a holiday weekend. At 70 mph it takes about 7.14 hours, but at 60 mph you only add about 30 minutes each way. Your fuel efficiency jumps from 30 mpg to 35 mpg, meaning you use 2.5 fewer gallons — saving $10 total, like finding gas for $3.40 instead of $4.00.

There is also a bonus beyond your bank account. On that same 500-mile trip, driving slower cuts your carbon dioxide emissions by more than 50 pounds. Carbon dioxide is a greenhouse gas that contributes to climate change. Using less of it is a simple way to help protect the environment.

The takeaway is clear: slowing down costs you very little time but saves real money and helps the planet. Next time you are on the highway, try setting your cruise control a little lower than usual. You might enjoy the scenery more, worry less about gas prices, and feel good knowing that physics is working in your favor.