How to Save Fuel on a Long Road Trip

On a long road trip, fuel is usually one of the biggest costs after lodging, and it is the one you have the most control over from behind the wheel.

The good news is that you do not need a different car or special gadgets to use less of it.

A handful of choices about speed, packing and preparation make a measurable difference over hundreds of miles.

The figures in this guide come from FuelEconomy.gov, the fuel economy site run for the U.S. Department of Energy and the Environmental Protection Agency, which summarizes research from Oak Ridge National Laboratory and others.

Your exact results will vary with your vehicle, but the direction of each effect is consistent.

Speed is the biggest lever on the highway

Road trips are mostly highway miles, and on the highway, speed matters more than almost anything else.

Every vehicle has its own most efficient range, but FuelEconomy.gov notes that gas mileage usually decreases rapidly at speeds above 50 mph.

Air resistance grows quickly as you go faster, so each extra mile per hour costs more fuel than the one before it.

Slowing down by 5 to 10 mph, while staying within the speed limit and keeping up with the flow of traffic, is one of the most effective changes you can make.

The site estimates a fuel economy benefit of roughly 7% to 14% for drivers willing to slow down by that much.

Over a 1,000-mile trip, that adds up to real savings, and the extra time is often smaller than people expect because you will stop less often to refuel.

Drive smoothly

Aggressive driving, meaning speeding, rapid acceleration and hard braking, wastes gas.

FuelEconomy.gov says it can lower gas mileage by roughly 15% to 30% at highway speeds and 10% to 40% in stop-and-go traffic.

On a road trip, that shows up when you weave through traffic, sprint away from every toll booth or brake late for exits.

A calmer style is also safer and less tiring on a long day.

Look far ahead, ease off the accelerator early when you see slowing traffic, and merge smoothly.

On open, flat highway, cruise control helps hold a steady speed, and the site notes that in most cases it will save gas.

In hilly terrain or heavy traffic, many drivers find it smoother to manage speed themselves.

Think twice about the roof box

Packing is where many road trips quietly lose efficiency. Anything on the roof disrupts the airflow over the car.

According to FuelEconomy.gov, a large, blunt rooftop cargo box 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 of 65 to 75 mph.

Rear-mounted cargo boxes or trays have a much smaller effect: about 1% to 2% in the city and 1% to 5% on the highway.

If you need extra space, a hitch-mounted carrier is the more efficient choice.

If you do use a roof box or bike rack, take it off as soon as the trip is over rather than leaving it on for weeks of everyday driving.

Pack lighter

Weight costs fuel too, though less than drag at highway speeds.

FuelEconomy.gov estimates that an extra 100 pounds in your vehicle could reduce mileage by about 1%, with a bigger effect on smaller cars than larger ones.

Before a long drive, clear out things that do not need to come along: sports gear from last season, boxes headed for donation, heavy tools you will not use. Pack what the trip actually needs.

Cut the idling at stops

Road trips involve plenty of waiting: in parking lots while someone runs inside, at scenic pull-offs, at long drive-through lines.

Idling can use a quarter to a half gallon of fuel per hour depending on engine size and air conditioning use, according to FuelEconomy.gov, and it only takes about 10 seconds' worth of fuel to restart a warm engine.

The site's guidance is that, as long as you keep engine starts to around ten per day on average, any shutdown longer than about a minute saves money. Vehicles with automatic start-stop systems handle this for you.

On very hot or cold days, of course, comfort and safety for passengers, children and pets come first.

Set up the car before you leave

A short pre-trip check pays off over the whole drive:

  • Tire pressure. Inflate all four tires to the pressure on the driver's door jamb placard, not the maximum on the sidewall. FuelEconomy.gov's maintenance page says proper inflation improves gas mileage by 0.6% on average and up to 3% in some cases, and that properly inflated tires are safer and last longer. Check them cold, before you head out, and recheck when the car is fully loaded if the placard lists a higher loaded pressure.
  • The right motor oil. Using the manufacturer's recommended grade of oil matters. The same page notes that using a heavier grade than specified, such as 10W-30 in an engine designed for 5W-30, can lower mileage by 1% to 2%. If an oil change is due, do it before the trip.
  • Warning lights. If the check engine light is on, have the car inspected before a long drive. FuelEconomy.gov points out it could be something minor like a loose gas cap or something that reduces fuel economy and leads to costly repairs.

Plan the route and the stops

Some of the easiest fuel savings happen before you start the engine.

Compare route options in your navigation app: a slightly longer route on open highway can use less fuel than a shorter one through congested city centers or stop-and-go construction zones.

Try to time departures to avoid rush hour in large metro areas along the way.

Plan fuel stops instead of waiting for the low-fuel light in a remote area, where prices are often higher and choices are few.

FuelEconomy.gov also offers a trip calculator that estimates fuel cost for a route based on your vehicle, which is handy for budgeting.

Air conditioning versus open windows

Many drivers wonder whether to run the A/C or roll the windows down.

Air conditioning adds load to the engine, and open windows add drag.

As a rule of thumb, open windows are reasonable at lower speeds around town, while on the highway the drag from open windows grows, so closing them and using the A/C moderately is usually the more comfortable choice.

Parking in the shade and venting hot air before you start driving also reduce how hard the A/C has to work.

A simple road trip checklist

  • Check tire pressure cold, at the placard number, before leaving.
  • Get any due oil change done with the recommended grade.
  • Use a hitch-mounted carrier instead of a roof box if you can, and remove racks after the trip.
  • Leave unneeded heavy items at home.
  • Cruise a few mph slower on the Interstate, within the limit.
  • Accelerate and brake smoothly, and use cruise control on open, flat stretches.
  • Turn the engine off for stops longer than a minute when it is comfortable and safe.
  • Plan the route and fuel stops ahead of time.

The bottom line

No single habit will cut your fuel bill in half, but together they add up over a long drive.

Slower, smoother highway driving and smarter packing are the biggest wins, and a quick check of tires and oil before you leave locks in the rest.

You will likely arrive less tired, too.

Sources and Further Reading