As Americans set out on popular Labor Day road trips to drink in the last dregs of summer, their joyrides will be the most affordable in more than a decade. A gallon of gasoline costs just $2.40 on average nationwide, which is the least drivers have paid since 2004, AAA reported.

South Carolina currently has the cheapest gas at just $2 a gallon on average and Alaska has the most expensive at $3.40 per gallon.

Gas prices have dropped as the cost of oil has tanked for the last year. The price of a barrel of oil has dropped from $100 to just $46. Subsequently, the price of gas has slid by more than $1 per gallon since Labor Day 2014.

“It is unbelievable that drivers are ending their summer vacations with the lowest gas prices for this time of year in more than a decade,” Avery Ash, an AAA spokesman, said in a statement.

It’s welcome news for drivers. On average, Americans save $15 to $25 every time they visit a gas station -- or about $50 a month -- thanks to lower fuel prices, CNN reported. Americans will collectively save more than $1 billion on gasoline just for the Labor Day weekend -- money they can instead use for other purchases, or stow away in savings.

Americans are also taking advantage of the opportunity to drive more for less. In the first half of 2015, Americans drove more than 1.5 trillion miles, according to the U.S. Federal Highway Administration -- a record high. And the savings aren’t over yet -- there is a seasonal slouch in driving just after Labor Day. This trend relieves demand for gasoline and can further drive down prices. In addition, many gas stations switch over to a winter-blend of gasoline Sept. 16, which is less costly to produce.

For those reasons, the U.S. Energy Information Administration estimates the national average price of gas could slide to as little as $2.11 a gallon by 2016. AAA expects prices to dip to less than $2 a gallon just in time for Christmas. Already, 5 percent of gas stations in the U.S. are selling gasoline for less than $2.

“There is good reason to believe that cheaper oil costs, a seasonal decline in driving and the switchover to less costly winter-blend gasoline will continue to push down prices through the end of the year,” Ash of AAA said.