By Rick Popely
Gas prices fell for the 42nd straight day on Thursday, pushing the national average for a gallon of regular unleaded to a four-year low of $2.95 as motorists across the country spent less at the pump every time they filled up. Even as motorists shell out fewer dollars per gallon, though, with winter approaching they are likely to get fewer miles per gallon in return because they are burning winter gasoline blends and driving in cold winter weather, two factors that hurt fuel economy.
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The EPA says mileage in city driving for a gas-powered car is about 12 percent lower at 20 degrees than at 77 degrees, and as much as 22 percent lower for short trips of less than 4 miles. Fuel economy for hybrids can drop even more, 31 to 34 percent, at that temperature. Cold weather takes a toll on fuel economy in a number of ways: It takes longer for the engine to reach normal operating temperature, when it achieves its best fuel economy. If you let your car run at idle for a while to warm the engine before you drive, you’re getting zero miles per gallon.
In addition, alternators have to work harder in cold weather to keep the battery charged, making the engine work harder. Using the heater fan, window defrosters and heated seats also add to the engine’s workload. Colder air is denser, increasing aerodynamic drag at highway speeds, and tire pressure drops along with the temperature (about a pound of pressure for every 10 degrees), increasing rolling resistance. Driving on snow- or ice-covered roads also can contribute to this automotive version of seasonal affective disorder. The EPA says slippery conditions decrease tire grip, so some of the energy used to power the drive wheels is wasted.
What all that adds up to is fewer miles per gallon, but six straight weeks of declining pump prices means that many motorists are spending significantly less when they fill up as the holiday season approaches. The average price for regular unleaded has fallen 39 cents since Sept. 25. The national average for regular unleaded reached a 2014 peak of $3.70 on April 28, but slipped below $3 on Nov. 1 for the first time since Dec. 22, 2010, and has continued to inch down.
The AAA Daily Fuel Gauge Report on Thursday listed 24 states as averaging less than $3 for regular unleaded, with four more within a few cents of that mark. Illinois, for example, which typically ranks among the more expensive states for gas, was at $3.03. AAA estimated that motorists can buy regular unleaded for less than $3 at more than 60 percent of gas stations around the country. South Carolina had the cheapest gas, averaging $2.70 for regular unleaded, followed by Tennessee, $2.71, and Mississippi, $2.73. Hawaii remained the only state in which gas averaged more than $4, but at $4.01 per gallon that could soon change.
As gas prices continued to fall, diesel fuel inched upward by fractions of a penny the past week to $3.604 (two tenths higher). Diesel fuel is 24 cents cheaper than a year ago, and regular unleaded is 28 cents cheaper.