Thanks largely to the booming energy industry, Montana drivers - particularly those who frequent two-lane highways - have been encountering more and more supersize truck traffic.

How big? One load that is coming up from the port of Houston and began its passage through Montana on Wednesday is 20 feet wide, slightly more than 20 feet tall and 290 feet long. It has 90 tires on 24 axles and weighs 917,000 pounds - so heavy that two trucks are attached to the rear to help push it along.

"When you've got a million pounds, that's a lot of strain on one truck," said Dan Kiely, chief of the state Department of Transportation bureau that issues permits for oversize loads.

The million-pound load consists of a steam condenser unit that will be use to process oil sands at a project in Saskatchewan. Many of the big loads are headed for the oil sands industry in Saskatchewan and Alberta, while other trucks are hauling giant generator blades and related equipment to a wind farm in Alberta. In the other direction, industrial equipment manufactured in Canada is being shipped to the booming natural-gas industry in Wyoming.

All those trucks and drivers, as well as pilot cars and their drivers, are giving a small but welcome boost to businesses in small towns across Montana.

"They're going to be staying at hotels and eating and fueling," Kiely said.

The traffic has been good for the Little Montana truck stop and cafe in Grass Range. Because the oversize loads are not supposed to travel by night, the Little Montana is a popular spot to pull over and spend the night for truckers passing through on Highways 87 and 200.

Despite their sometimes enormous size, the trucks apparently haven't been causing too many problems for other drivers.

Gary Smith, owner of the Little Montana and of G.S. Oil in Roy, said the drivers of the big rigs keep a close eye on traffic and will do what they can to help traffic get around them.

"They're real good," Smith said. "You just go right around them. Those guys are real good, real accommodating."

Montana Highway Patrolman Dan Ohl, who has been working out of Malta for four years, said some of the loads are too wide to be passed safely, so the truckers will temporarily pull over to let other motorists by.

"I haven't had very many problems," he said.

Any truck with a load wider than 8 feet 6 inches has to obtain an oversize-load permit. Last year, the state issued 63,021 such permits, up from 56,506 in 2007 and 55,063 in 2006.

Special permits are required for trucks bearing what Kiely called "superloads." There are three classes of superloads, based on weight, height, length and width. In the first class are loads wider than 18 feet but narrower than 34 feet, or those over 17 feet high but under 24 feet.

The second class is for trucks over 34 feet wide or 24 feet high, or longer than 200 feet. In the third class are all loads heavy enough to require notification of the bridge bureau, to make sure all bridge crossings are safe. In 2008, the state issued 1,337 permits for superloads, down from 1,754 permits in 2007 and 1,433 in 2006.

Kiely said companies shipping superloads have to notify his bureau of their exact route through Montana, after which the Transportation Department passes the information on to every affected county road department, so that any special local conditions can be noted and planned for. That process can take up to five days, he said.

Charity Watt Levis, a spokeswoman for the Department of Transportation, said people occasionally ask why so many of the big loads are on two-lane roads rather than on the larger interstate highways. The answer is simple, she said: "Oftentimes they're too tall to go under the interstate overpasses."

The 290-foot-long steam condenser load, for example, entered Montana south of Broadus on Highway 59 and was to head north to Miles City, briefly travel on Interstate 94, then take Highway 12 nearly to Baker, bypassing that town on two county roads before heading north to Wibaux and then - five or six county roads and two-lane highways later - to the border crossing at the Port of Raymond.

Another well-used route to Canada has trucks taking Highway 59 to Jordan, west on Highway 200 to Grass Range and then to Canada through Malta or Fort Belknap. Other loads go farther west to use the big Sweet Grass border crossing north of Shelby.

Kiely said one oil sands company has already notified the state of plans to bring up to 300 superloads through Montana in 2010 or 2011. Those shipments will originate at a factory in the Far East, go by ship to the West Coast and then by barge up the Columbia River system to Lewiston, Idaho, where they will be loaded onto trucks.

Those shipments will enter Montana over the narrow, winding Lolo Pass southwest of Missoula, and Kiely said the company is planning to make test runs with empty containers to see how large a load each truck can carry.

All trucks have to pay gross vehicle weight fees and overweight permit fees, and the state tries to weigh each one somewhere on its passage through the state, to make sure it is meeting the gross-weight and per-axle weight limits.

The companies have good reason not to fudge on their permit applications, Kiely said. If there are discrepancies between what they actually weigh and what it says on the permit, the truck may have to sit at the weigh station until another permit is applied for and issued - again after going to every county road department on the proposed route.

Nobody wants trucks sitting idle for up to five days, Kiely said, especially when shipping costs are so high. He said he was told that shipping the steam condenser unit would cost the company $15,000 a day.

John Hanson, co-owner of Whitewood Transportation in Billings, said the superloads are "kind of becoming an industry standard."

Especially when shipping industrial components to places like Canada, where wages are high and conditions harsh, it makes economic sense to assemble ever-larger pieces in foreign factories and put them together on site.

"Things just keep getting bigger," Hanson said.

With the really big loads, Hanson said, "logistically it's a nightmare." Pilot cars are often sent out in advance to map out the entire route, to make sure the roads and bridges can handle the loads.

"You don't just take off down the highway with one of these loads and hope for the best," Hanson said.