MINNEAPOLIS — From behind the wheel of his big rig, Eric Feehan can't quite envision a future when 18-wheelers drive themselves.

"There are so many variables, I don't think anybody's going to make it work," the Minnesota truck driver said during a break in Sparks, Nev.

In 24 years on the road, Feehan has learned that it takes experience and instinct to react when your truck is buffeted by 40 mph winds, to sense the moment when wet highways turn to ice, or to anticipate when a car is going to swerve in front of you.

"There's no way they're ever going to program that into a self-driving truck," said Feehan, who lives near the Twin Cities and regularly drives to Arizona and California.

They're working on it, though. While advancements in autonomous — or self-driving — cars get much of the attention, development of self-driving commercial vehicles is speeding forward. Complex questions involving safety, security, liability, regulations, and infrastructure remain, making widespread use years away, but trucks that operate with minimal driver involvement are being tested now. Tesla will unveil an electric autonomous semi on Oct. 26, and most major truck makers are working on versions.

The Trump administration is encouraging progress with what it calls a "nonregulatory approach" to autonomous vehicles, which means that it wants as few rules as possible. That has exacerbated some safety concerns.

"When we're talking about vehicles … the size of a house going 70 mph down our freeways," said Jason Levine of the nonprofit Center for Auto Safety in Washington, "there's a real concern that the technology isn't ready yet to be released into the wild."

In the early stages, experts say, some kind of technician or operator would still be in the cab. But the end goal is a truck that could drive itself.

Proponents note that 94 percent of traffic deaths are caused by human error. In theory, there would be fewer as self-driving vehicles multiply.

"This technology is not just coming; it's here," said John Hausladen, president of the Minnesota Trucking Association, which has a task force on autonomous vehicles that met for the first time in September.

Gary Pressley, a task force member and president of Heavy Metal Truck Training in suburban Minneapolis, said that activity is picking up. Last month, the issue was among topics he discussed at a retreat held by a trucking company in Green Bay, Wis., and at a national meeting of the Commercial Vehicle Training Association in San Antonio, Texas.

"We're talking years and years of testing and acceptance" before autonomous trucks become commonplace on America's roads, Pressley said. "It's not going to be next year. … But it is coming."