Louisville gas prices have fallen more than seventy cents in three weeks. The average price for a gallon of regular unleaded today in Louisville is $3.42. It’s down from $4.16in mid-September.AAA’s Roger Boyd says the primary factor is the price per barrel of oil."That’s the villain whenever prices go up, it’s also going to be the good news whenever costs go down," says Boyd. "We’ve seen that prices dropping significantly, somewhere into the 90’s, which estimates and even dropping sometimes below that."Boyd says some economists attribute the drop to a strengthening U.S. dollar. He says Hurricane Ike’s relatively light impact on Gulf Coast refineries is also a factor.