Today’s cars may be more reliable than those of years ago, but somehow, a road trip just seemed a bit more exciting when the primary question was whether or not you’d make it to your destination at all. But you may find yourself encountering a whole new kind of thrill if you wind up spending your last 50 cents on gas when you need 65 cents to feed the parking meter at your destination. So, while doing math may not be as fun as, say, replacing a head gasket in Paducah, planning for fuel expenses remains a vital part of any cross-country tour. 

You Mileage May Vary

Before going on a road trip the first and most important step in estimating mileage is to find out what kind of fuel economy you’re dealing with. You car’s EPA city and highway ratings are a good starting point, but they’re far from absolute. Think of the EPA rating system as a kind of yardstick; the government mandates the same testing conditions and procedures for all vehicles tested. This allows us to compare the relative fuel efficiency of different vehicles, but variances of 10 percent or more are fairly common, even for brand-new cars under the most controlled conditions. So, test your car’s real-world city and highway mileage beforehand — it will be affected your car’s weight and equipment, and your driving style.

Testing Procedures

The best way to check your car’s fuel economy is to perform a two-way average, or “round trip,” test. To perform this test for highway mileage, fill your tank up to the brim at a gas station next to an interstate on-ramp. Reset your trip odometer (or write down your odometer reading if you don’t have a trip function), and accelerate up the on-ramp to your typical cruising speed and set the cruise control. Go 50 or so miles, turn around, and then tank up back at the same gas station. Divide miles driven by gallons pumped, and you’ve got the highway mileage. Perform this same test in the city by driving a random route through town, following a mix of faster and slower roads, and then fill back up at the same gas station.

Measuring Cities

Any online mapping program or GPS system will give you a precise mileage from doorstep to doorstep, so take advantage of technology to plan your route on a computer beforehand. However, mapping programs won’t tell you how many mpg you’ll gain or lose in a city. Check your mapping program or map for the distance you’ll travel through any city on the interstate; you may wish to just measure across the beltway that runs around many large cities, and add approximately 10 miles to that to catch the whole metro area. For instance, Atlanta, Georgia measures 20 miles on I-75 from one side of the 285 beltway to the other; add 10 miles (for a total of 30 miles) to get you from the suburb of Morrow in the south to Marietta in the north, and you’ve covered the Atlanta metro area.

Accounting for Cities

If your route will take you through a city at anything other than morning or evening rush hour, and you’re not getting off the interstate, then you’d do best to ignore it. While on your road trip going through a city on the interstate at a steady speed may actually net you better fuel economy, due to the lower speed, but you can’t count on the exact amount of increase. For every city you plan to hit during rush hour (about 6:30 to 8:30 a.m., and 4:30 to 7:00 p.m.), subtract the distance across that city from your total trip mileage. Subtract the city diameter for every city you pass through on non-interstate roads. For instance, you’d subtract 30 miles from the total if you plan to hit Atlanta’s I-75 at rush-hour, or if you’re going to trek the ATL on US-41 (the highway paralleling I-75 through downtown).

Calculating Fuel Economy

Divide your adjusted trip mileage (minus the city count above) by your measured highway mpg in order to determine how much fuel you’re likely to burn on the open road. Now, divide the city mileage you subtracted (30 miles in the A-Town example) by your measured city mpg. Add your city-burned fuel to the highway-burned fuel to get a final total of how much fuel you’ll use to get from Point A to Point B. Remember, you’re accounting for every city you’ll pass through on non-interstate roads the same as you would for hitting the city’s interstate at rush hour.

Sassy Peeps, When taking a road trip, how do you determine the amount of gas you will spend? Inquiring minds would like to know!

Have A Happy Healthy, and Remember to Always…
Stay Sassy!


Collin Whittaker

Collin is the editor and owner of The blog/website came to life out of his passion for the automotive industry. He has 15 years of experience and has worked for companies like Honda, Nissan, Firestone, and many other auto repair shops. Collin is a husband and a father to three beautiful kids.

His goal is to share his expertise and knowledge of the automotive industry in hopes of helping many car owners keep their cars reliable, safe, and enjoyable.

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