WASHINGTON (MarketWatch) — So, what are Americans doing with some of the money they’re saving from cheap gas? They are buying more fuel.

Plunging prices are encouraging Americans to drive more often and buy more trucks. At the same time, faster economic growth and a big influx in hiring over the past year means more Americans are now taking part in the daily commute.

The result: sharply higher demand for gasoline, argues Nicholas Colas, chief market strategist at ConvergEx.

“We’ve finally discovered where American consumers are spending some of the savings from lower gasoline prices: they are buying more gasoline,” he said in a new report.

For one thing, Colas points out the amount of gasoline supplied to the U.S. market was up 6.3% in January compared with a year earlier.

What’s more, the number of miles Americans drive annually was on track to surpass 3 trillion in 2014 for the first time since a record 3.04 trillion in 2007 — the year before the Great Recession started. (The government estimates miles driven via thousands of electronic sensors on main public roads.)

It really shouldn’t come as a surprise that Americans drive more when gasoline prices fall. That is always been the case. And an improving economy has accelerated the trend.

In 2014, for example, the U.S. added 3.1 million jobs. More than half were generated in the final six months of the year, just as gasoline prices began to free fall.

What that translates into is many as 2.25 million new commuters. How do you get to that figure? Well, a 2013 report by the U.S. Census estimated that 76% of Americans drive to work alone. (An additional 11% ride in a car with someone else.)

Spending at gas stations appears to support the idea that car drivers are putting more fuel in their vehicles even as prices fall. The retail cost of regular gas fell by about 37% from July through December, but U.S. sales at gas stations dropped a smaller 25%.

The dramatic drop in gasoline prices – to less than $2 a gallon in many parts of the country – is also boosting sales of less fuel efficient trucks. GM, for example, said sales of trucks and crossovers were up 42% in January vs. a year earlier. The release of the new Colorado midsize pickup helped perk up GM sales, but other auto makers also reported double-digit percentage gains in truck purchases.

One thing that is had little impact on overall American driving habits is fuel efficiency standards, Colas argues. Dividing miles driven by gasoline consumption suggests the average vehicle gets about 20 to 21 miles per gallon today, virtually unchanged since 1980.

While battery-operated cars and hybrids get a lot of ink, sales of trucks have soared compared with 35 years ago to easily outweigh the impact of more fuel-efficient vehicles on the road today.