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Driving More Efficiently

Drive Sensibly
frustrated driver

Updated Information

Aggressive driving (speeding, rapid acceleration and braking) wastes gas. It can lower your gas mileage by roughly 15% to 30% at highway speeds and 10% to 40% in stop-and-go traffic.1

Driver feedback devices can help you drive more efficiently. A recent study suggests that they can help the average driver improve fuel economy by about 3% and that those using them to save fuel can improve gas mileage by about 10%.2

Sensible driving is also safer for you and others, so you may save more than gas money.

Fuel Economy Benefit: 10%–40%
Equivalent Gasoline Savings:
Observe the Speed Limit
Graph showing MPG decreases rapidly at speeds above 50 mph

While each vehicle reaches its optimal fuel economy at a different speed (or range of speeds), gas mileage usually decreases rapidly at speeds above 50 mph.

You can assume that each 5 mph you drive over 50 mph is like paying an additional $0.18 per gallon for gas.3

Observing the speed limit is also safer.

Step 1. Select a vehicle.

Selected Vehicle

Step 2. Enter your fuel cost and speed information.

I pay $ /gal for .

Understanding the Charts

Cost/Gallon: When driving 50 mph, price per gallon is assumed to be the same as the pump price. At higher speeds, the estimated price per gallon is increased based on the additional fuel you use by driving faster. The price of fuel doesn't actually go up, but this is a useful way to put the cost of driving faster in context.

Cost/Gallon = Fuel Price at Pump × Est. MPG at Higher Speed
÷ Est. MPG at 50 MPH

Cost/100 Miles: This is useful for estimating fuel costs for long trips.

Cost per 100 Miles = Fuel Price ÷ Estimated MPG × 100

Save Money: This graph shows how much money you can save by slowing down. Cost per gallon and cost per 100 miles show the difference in cost at your typical highway speed and the cost at the reduced speed.

Savings per extra time incurred is calculated as the money saved by slowing down divided by the extra time incurred:

Savings = (Fuel Price * (1 ÷ MPGT)-(1 ÷ MPGR)) ÷ ((1 ÷ SpeedT)-(1 ÷ SpeedR))


  • MPGT = fuel economy at typical highway speed
  • MPGR = fuel economy at reduced highway speed
  • SpeedT = typical highway speed
  • SpeedR = reduced highway speed

The Study

Speed-mpg relationships are based on dynamometer tests of 74 light-duty vehicles representing a variety of manufacturers, nine vehicle classes, engine sizes 1.5 L to 6.2 L, and model years 2003 to 2012. Almost all are conventional gasoline-powered vehicles. Only one diesel and two hybrids are included; no plug-in hybrids or electric vehicles were tested.

These estimates work best for well-maintained modern gasoline light-duty vehicles and will likely be less accurate for diesels, hybrids, and vehicles with cylinder deactivation. Their applicability to plug-in hybrids and electric vehicles is unknown.

We estimate vehicle MPG at steady-state cruising speeds based on the vehicle's EPA "highway" fuel economy rating. These estimates are typically higher than both the EPA highway MPG ratings and the MPG consumers experience in on-road highway driving. Therefore, our cost and savings estimates should be conservative.

Fuel Economy Benefit: 7%–14%*
Equivalent Gasoline Savings:
* Average savings, assuming drivers are willing to slow down 5 to 10 mph and fuel costs $2.63 per gallon.
Avoid Hauling Cargo on Your Roof
Vehicle with roof rack

Hauling cargo on your roof increases aerodynamic drag (wind resistance) and lowers fuel economy.

A large, blunt roof-top cargo box, for example, can reduce fuel economy by around 2% to 8% in city driving, 6% to 17% on the highway, and 10% to 25% at Interstate speeds (65 mph to 75 mph).4

Rear-mount cargo boxes or trays reduce fuel economy by much less—only 1% or 2% in city driving and 1% to 5% on the highway.

If you need to use an external cargo container, removing it when it's not in use will save fuel and money.

Fuel Economy Benefit: 2%–17%
Equivalent Gasoline Savings: $0.05–$0.45/gallon
Remove Excess Weight

Avoid keeping unnecessary items in your vehicle, especially heavy ones. An extra 100 pounds in your vehicle could reduce your MPG by about 1%.5 The reduction is based on the percentage of extra weight relative to the vehicle's weight and affects smaller vehicles more than larger ones.

Fuel Economy Benefit: 1%/100 lbs.
Equivalent Gasoline Savings:
Avoid Excessive Idling

Idling can use a quarter to a half gallon of fuel per hour, depending on engine size and air conditioner (AC) use. Turn off your engine when your vehicle is parked. It only takes about 10 seconds worth of fuel to restart your vehicle.6

Turning your engine off when your vehicle is parked can save you money. Here are some tips to help you maximize your savings.6

Best Practices

  • Limit engine starts to about 10 times per day on average—unless your vehicle is equipped with a start-stop system. Occasionally exceeding this limit should not cause excessive starter wear.
  • Assuming 10 starts a day aren't exceeded, any shutdown longer than 1 minute will save money.
  • Limit electric accessory use during shutdown, particularly during longer shutdown periods.
  • Drive at least 5 miles between start cycles to fully recharge the battery.

If you'd like to promote idle reduction in your area, the Clean Cities IdleBox Toolkit can help you get started.

Fuel Cost Savings:
$0.01–$0.02/min. (AC off)
$0.02–$0.03/min. (AC on)
Use Cruise Control

Using cruise control on the highway helps you maintain a constant speed and, in most cases, will save gas.

Note: Cost savings are based on an assumed fuel price of $2.63/gallon.
View Data Sources…
  1. Thomas, J., S. Huff, B. West and P. Chambon. 2017. Fuel Consumption Sensitivity of Conventional and Hybrid Electric Light-Duty Gasoline Vehicles to Driving Style, SAE Int. J. Fuels Lubr. 10(3):2017, doi:10.4271/2017-01-9379.
  2. Institute of Transportation Studies, University of California, Davis. ECODRIVE I-80: A Large Sample Fuel Economy Feedback Field TestAdobe Acrobat Icon (ITS-RR-13-15).
  3. Estimates for the effect of speed on MPG are based on a study by Oak Ridge National Laboratory (ORNL): Predicting Light-Duty Vehicle Fuel Economy as a Function of Highway Speed, SAE 2013-01-1113.
  4. Oak Ridge National Laboratory. 2014. Fuel Economy and Emissions Effects of Low Tire Pressure, Open Windows, Roof Top and Hitch-Mounted Cargo, and Trailer (SAE 2014-01-1614). Study results are based on testing with a small sedan, a standard size SUV, a single roof-top cargo box (20" H x 40" W x 50" L), and a single rear-mount cargo tray. Cargo boxes with other dimensions or shapes may have a different effect on fuel economy.
  5. Based on a fuel economy improvement of 0.33% per 1% reduction in weight as estimated by Ricardo Inc., Impact of Vehicle Weight Reduction on Fuel Economy for Various Vehicle Architectures, April 2008. Our estimate assumes a vehicle weight, including cargo, of 3,200 lbs.
  6. Argonne National Laboratory. 2015. Stop and Restart Effects on Modern Vehicle Starting System Components – Longevity and Economic Factors.