The young woman frowned at the Kroger gas station sign on Sunday. Unleaded gas, the bane of her monthly budget, was suddenly $2.60 per gallon. Unfortunately, her tank was nearly full.

She mourned the lost savings.

Brittany Tripp Schulz, 24, lives in Murfreesboro, Tenn., with her husband, Danny. Each day, she commutes 70 miles round-trip to her recruiting job at a Nashville insurance company. Her gas light flashes every six days.

“I thought, ‘Why? Why can’t it be this cheap when I’m empty?” Schulz said. “I don’t expect that price to last.”

Filling up her silver Nissan Altima usually costs $55. Lately, $45. Schulz, who records each expense on an Excel spreadsheet, first noticed declining fuel prices in September. She can’t believe they keep dropping.

This week, for the first time in four years, average U.S. gas prices dipped below $3 per gallon — an economic boost for consumers who have come to expect paying more at the pump. The bottom fifth of American earners spend up to 13 percent of their income on gasoline.

Many, however, see the recent price drop as a rare bonus with good timing. A common sentiment: Celebrate, but don’t get used to it.

Gallup polls from the past seven years reveal our national tendency to brace for  higher gas prices over and over again. When they spike, we blame the president, Congress, oil companies and the Middle East (but seldom express surprise). When they dip, we’re hesitant to return to happy-go-luckier driving habits.

The defining trait of American gas prices over the last two decades is fluctuation — and public opinion hasn’t recovered from the whiplash. As Washington Post columnist Catherine Rampell noted recently, overall household income is actually lower than it was when the recession ended, which has only added to commuter angst and apprehension.

“Anecdotally, we’re hearing that consumers tend to think gas prices will head back up,” AAA spokesman Michael Green said. “Most see no hope for long-term lower gas prices.”

More than 60 percent of U.S. stations are now selling gas below $3 per gallon, according to GasBuddy.com. South Carolina and Tennessee are tied for the lowest state average at $2.75 per gallon.

Compare that to gas prices in June, which hovered around $3.60 per gallon, according to AAA. Drivers whose pockets feel fatter can thank America’s shale revolution, which, experts say, is pushing Saudi Arabia to lower crude oil prices.

Gas money saved tends to manifest as discretionary spending elsewhere: an extra sack of groceries, a new television, another holiday gift to wrap. “And it will put more people on the road,” said Chris Christopher, director of consumer markets at IHS. “This is especially helpful for people who can’t afford airfare. People are more likely to drive — and drive longer distances — this season.”

But they’re less likely to incorporate gas savings into any long-term financial plan.

Every dollar helps Schulz, who recently bought a three-bedroom house. Her husband, who studies exercise science at Middle Tennessee State University, plans to work full-time after he graduates in 2016. For now, they’d rather stash away savings than dine out often.

But soon, the highways will be slick with ice. Fall foliage will fade to bare branches. And the gas prices, Schulz believes, will surge.

She and her husband will pour what they deem temporary financial relief into a temporary indulgence: A 300-mile road trip to visit friends and drink beer in Columbus, Ga. This round-trip drive will cost about $80, Schulz estimates. She wants to take advantage of the bargain before it expires.