Americans renewed their long-standing love affair with the automobile in 2015, challenging the notion that millennials and baby boomers alike are abandoning their cars for public transit, bikes and car-sharing.

Last year, U.S. motorists drove more miles — 3.148 trillion — than any other year in history, according to data released by the Federal Highway Administration last month. And about 17 million new cars and trucks were sold in 2015, an increase of nearly 6 percent and a level of car commerce not seen since 2000.

Why?

The FHA, which logs miles driven by car, bus and truck drivers, is reluctant to speculate. "We just know there are more cars out there and they're going farther," said spokesman Doug Hecox.

It could be historically low gas prices. The Twin Cities' average price of $1.98 per gallon on Thursday is far less than the highest price per gallon ever recorded — $4.29 per gallon — in May 2013, according to the AAA.

"People may be more likely to take a road trip vs. staying at home or flying somewhere," said Bill Holloway, a transportation policy analyst at the State Smart Transportation Initiative in Madison, Wis.

Low prices at the pump aren't the main reason people are buying more cars; that's likely due to a stronger economy, said Haig Stoddard, senior industry analyst for Wards Auto. But gas prices may have spurred last year's 13 percent increase in sales of pickups, vans, sport utility vehicles and crossovers, which guzzle more fuel.

The outlook for sales remains strong, in part because so many families delayed new-car purchases during the Great Recession and its stodgy recovery.

"There are a lot of vehicles on the road that are very old, which will lead to some replacement," Stoddard said. "You hear that vehicles built today last longer," and people tend to keep them longer, too.

Woodbury resident Ken Roberts owns two cars — a 2002 Mitsubishi with 285,000 miles, and a 2000 Chevrolet Cavalier that has clocked some 272,000 miles — and plans to drive both "into the ground." The main criteria for a new vehicle is "four doors and good gas mileage," he said, pointing out his 48-mile one-way commute to Center City.

In Minnesota, a flattening

Yet another long-term trend suggests the romance of the open road may be less than it seems.

In Minnesota, vehicle miles traveled, or VMT, was flat between 2004 and 2014, after decades of increases, according to Gene Hicks, director of the traffic forecast and analysis section of the state Department of Transportation. While final numbers aren't yet available for 2015, he expects about a 3 percent increase. A 2015 MnDOT report says that even as the population has been increasing, per capita vehicle miles traveled has decreased in both the metro and non-metro areas.

Some of the decline has been attributed to millennials, the booming generation of 74 million Americans born between 1983 and 2000. A 2014 report released by the U.S. Public Interest Research Group indicates the average number of miles driven by 16- to 34-year-olds dropped by 23 percent from 2001 to 2009. This was due to young people taking fewer trips, shorter trips, and a larger share of trips by modes other than car. The fact that young people delay getting their driver's license figures, too.

But that doesn't mean millennials are not buying cars. Gen Yers now account for more than a quarter of all new-car sales, second only to baby boomers, according to J.D. Power & Associates.

Still, transportation analyst Doug Short of Advisor Perspectives anticipates that people young and old will continue to drive less in coming years due in part to the ubiquity of technology that enables work to be done remotely — mitigating the need to commute by car.

Short also cites a "general reversal of the flight to the suburbs," particularly by baby boomers, which also diminishes the need to drive. And shopping online has increased so dramatically since the turn of the century, it decreases trips to the mall or grocery store.

"As people grow older, they drive less," he said. "They may travel, but for a lot of people, travel doesn't involve driving around in their car."

In Chanhassen, the Larsen family's transportation strategy is more practical than anything. It involves determining which one of their aging automobiles, each with more than 200,000 miles on the odometer, will die first. Then — and only then — will the family of six buy a new car.

"I suspect our Honda Odyssey will go first," said Andrew Larsen, noting his minivan's tenuous transmission. "It's kind of on borrowed time."

A heavy load of freight

Nationally, U.S. DOT expects a 43 percent increase in commercial truck shipments, partly due to the explosion of e-commerce, and anticipated population growth of 70 million by 2045. Even though people may be driving less on a per capita basis, "an increasing population with increasing freight demands still leads to more and more total miles traveled and more challenges on the road ahead," the Transportation Department reported.

In December, President Obama signed the FAST Act into law, which will invest $305 billion in America's transportation infrastructure over the next five years, including $226 billion for roads and bridges. How Minnesota lawmakers will tackle transportation issues this legislative session is unclear — last year, there was a deep divide between DFLers and Republicans over how to fix the state's aging infrastructure, and whether to expand public transit like the $1.79 billion Southwest light-rail line. At a joint hearing of the House and Senate transportation committees in February, both sides vowed to at least try to reach a mutually palatable plan.

But nationally known smart-growth advocate Chuck Marohn says, "For so long the embedded assumption [of policymakers] is that increased auto miles equals greater economic development. I've argued that we've crossed the threshold of diminishing returns."

Road projects resulting from programs like the FAST Act "gin up the economy in the short term," he said, but the real question is "how do we make more productive use of all the stuff we've already built and are struggling to maintain?"

Marohn, founder and president of Brainerd-based Strong Towns, characterizes discussion of millennials and boomers scorning cars as "silly. Try living in this state without a car. There are very few places [here] you can actually do it and enjoy any success or affluence.

"It should not surprise anyone that millennials out of college move out of Uptown, get a job in the suburbs and wind up getting a car and driving," he said. "Because that's the economy we have built."

Janet Moore • 612-673-7752 Twitter: @MooreStrib