There are several ways you can improve your vehicle's fuel efficiency, from removing excess weight to setting the cruise control while on the highway. But you won't know how effective these efforts are unless you track your fuel economy.

Newer vehicles typically include a trip's fuel economy in the dashboard display or infotainment system. However, this reading may not always be accurate. A 2013 report by The Detroit News found that the miles per gallon suggested by a vehicle system were usually about 5 percent higher than reality. In the same year, the automotive site Edmunds.com determined that some vehicle displays overstated their fuel economy by nearly 20 percent.

Testing your vehicle's fuel economy figures is a fairly simple process, as long as you don't mind crunching some numbers. If you get into the habit of checking it after each stop at the pump, you can see how well your vehicle is performing and whether a drop in fuel economy may signal a problem.

When you stop for your next fill-up, make sure you refill the tank until the pump shuts off. Then make a note of the mileage on the odometer. The next time you need to refuel, again fill the tank to the top. Then take down the number of gallons the fill-up required and the new figure on the odometer.

Subtract the old odometer figure from the new one to determine how many miles you traveled on the previous tank of gas. Then divide this figure by the number of gallons it took to fill the tank to determine how many miles you averaged per gallon.

Many vehicles have a trip odometer to simplify this process. The Department of Energy says you can reset this separate odometer after you refuel to record how many miles you travel on your next tank of gas. The next time you stop at a station, fill up the tank and divide the trip odometer recording by the number of gallons you put in to calculate your mileage.

Drivers can also use this data to calculate how much their travel costs are. MissouriFamilies.org, a resource of the University of Missouri Extension, says dividing the fuel economy figure by the price of gas at the time of the initial fill-up will let you know how many miles each dollar's worth of fuel is getting you. Similarly, dividing the price of fuel by the vehicle's fuel economy will give you a figure for your fuel costs per mile.

Calculating your driving costs can help you determine if it's time to switch to a more efficient vehicle. For example, Edmunds.com offers a calculator allowing you to compare your current vehicle to a more efficient model, including factors such as gas prices, the vehicle's purchase price, how many miles you typically drive, and your current vehicle's trade-in value. These figures allow you to calculate how much you'll save through better fuel economy and how long you'll need to own the more efficient vehicle before the savings offset the purchase price.

Naturally, the fuel economy figures you calculate for a vehicle will fluctuate. You'll get a higher value for a trip with a lot of highway travel than you would for a trip with stop-and-go travel in the city.

Other factors will also affect your fuel economy as well. The Department of Energy says your fuel economy is reduced by about 1 percent for every 100 extra pounds you are carrying, so your mileage will drop if you are frequently carrying passengers or cargo. Speeding, idling, and rooftop cargo containers can also make your vehicle less efficient.

You're likely to see a prolonged dip in fuel economy during the winter. This stems from a number of different causes, including the lower energy offered by winter blend gas; increased wind resistance from cold, dense air; and the decision by many drivers to idle their vehicle for a few minutes to help it warm up before a trip.

If you notice that your fuel economy has fallen and there isn't an obvious reason for it, you might want to have your vehicle inspected for problems. The automotive site CarsDirect says an unexpected drop in efficiency may result from issues such as a faulty oxygen sensor or air filter, using the incorrect type of motor oil, misfiring spark plugs, or a problem with the fuel injection system.