Average U.S. gas prices have fallen below $4 per gallon for the first time since March, though costs are still higher from a year ago. The national average price of a gallon of regular gasoline is $3.999 as of Thursday morning, according to AAA. That’s down 13 cents from a week ago and more than half a dollar from a month ago. Prices have come down significantly on news of President Donald Trump’s deal with Iran, which led to the Strait of Hormuz reopening for the first time since March.