Here's the setup: You drive a 2012 model-year vehicle, so by the federal government's estimate, that vehicle can travel 28.2 miles on a gallon of gasoline. Let's say you drive a car that is powered just by electricity. Lucky you. Based on the average cost of a gallon of gas, you can drive that car 28.2 miles for $1.03, according to the U.S. Department of Energy, which announced the launch of an online calculator that compares the costs to drive gasoline- and electric-powered vehicles. Click here to run the numbers. According to the Energy Department, nearly 50,000 plug-in electric vehicles were sold last year in the United States. Brittany Bungert, of the Iowa Automobile Dealers Association, checked her sources and found that about 3.38 percent of all vehicles sold last year in the nation were plug-ins or hybrids. Using that figure, she estimated that about 4,408 vehicles traveling Iowa roads are electric-only or gasoline-and-electric hybrids.