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

How overmuch does your mileage alteration with speed? Every car is different, but the US Department of Energy estimates that for each 5 mph summation successful velocity implicit 50 mph, substance ratio declines by 7 percent. In equation form:

Here e₀ and v₀ are the ratio and velocity astatine immoderate benchmark, and this tells you the ratio for immoderate different velocity. The 0.93 is that 7 percent decrease. Let's bash a speedy example. Maybe your car gets 30 mpg (e₀) astatine a velocity of 70 mph (v₀). Then astatine 75 mph it would get 27.9 mpg, and astatine 65 mph it would get 32.3 mpg. See however that works?

Time and Money

Now let's propulsion this each together. If you thrust faster, you prevention time. But you usage much fuel, truthful it costs more. What are the presumption of the trade-off?

Let’s spell backmost to our 30-mile trip, and I’ll presume state costs $4 a gallon. If you thrust astatine 70 mph with an ratio of 30 mpg, you usage 1 gallon of gas, which costs $4.00. Bump the velocity up to 75 and you usage 1.08 gallons, for an other outgo of 32 cents. No large whoop, right?

But remember, you’re lone redeeming 1.7 minutes, oregon 0.028 hours. If we disagreement the added outgo by the clip savings (0.32/0.028), that’s a punishment of astir $11.15 per hr saved.

Finally, let’s accidental you person a 500-mile circular travel thrust planned for the July 4th weekend. If you acceptable cruise power to 70 mph, that’ll beryllium 7.14 hours of driving. Cut that to 60 mph (10 mph less) and you’re looking astatine an other 30 minutes down the instrumentality each way.

But your substance ratio volition summation from 30 to 35 mpg. That means you’d usage 2.5 gallons little to thrust the aforesaid distance, for a outgo savings of $10. Or different mode to deliberation astir it: Driving successful the dilatory lane is equivalent to paying $3.40 a gallon for state alternatively of $4.00 a gallon.

You’d astir apt spell retired of your mode for that benignant of terms difference, right? Oh, and you’d trim your CO₂ emissions by much than 50 pounds for the trip. So my advice? Ease up connected the pedal, easiness up connected the planet, and bask the scenery.