In the last three years, engine production at Volvo Powertrain - the plant formerly known as Mack Trucks - rose by close to 70 percent and transmission production roughly tripled, according to company data.
To keep up, the company added about 700 employees over that period, for a current total of around 1,700.
The Volvo Powertrain plant off Pennsylvania Avenue makes heavy-duty and medium-duty truck engines and transmissions for Volvo and Mack.
Volvo acquired Mack and Renault in 2001.
The Washington County plant expects to produce three new engine models in 2007, when tighter federal emission standards begin.
According to the U.S. Environmental Protection Agency, heavy-duty trucks and buses starting with that model year must run much cleaner, toward a goal of cutting harmful pollution by 95 percent. The EPA decided on the plan in 2000.
Aronsson said the emission of fine particles must be cut to one-tenth of its current level and the level of nitrogen oxide must be cut by half.
Pollution can lead to ozone buildup and irritants in the air, which could cause or aggravate health problems.
Mack and Volvo are preparing for a drop in the market in 2007 because of the new emission standards that begin then.
"There'll be some downturn," said Kevin M. Flaherty, Mack Trucks' senior vice president of sales. "The jury is out how deep that's going to be."
Flaherty said one market factor is a shortage of about 40,000 drivers in the heavy-truck industry.
Volvo Powertrain's plant upgrade includes a $35 million, 102,000-square-foot engine testing laboratory.
The four-story building will open in the middle of 2006 with eight identical engine test cells, said Jim Morris, director of the lab.
Other money is being spent to refurbish the current plant, which is 44 years old.
New technology will be introduced, too. On the tour, Aronsson stopped in front of a pair of electronic arms that lift and assemble heavy engine components - without needing a break, he noted.
Employees talked about and showed how mechanization helps their duties. At one stop, a machine lifted, turned, rotated and tilted a massive engine, giving a worker full, effortless access to almost every inch.
Aronsson said ergonomics is emphasized as changes are made. The current assembly line's floor is wood, rather than concrete, reducing the stress on employees who stand all shift, he said.
Last month, U.S. Sen. Barbara Mikulski, D-Md., stopped at the plant to talk about a pending proposal for $3.5 million in federal money to help Volvo Powertrain build four prototype hybrid electric trucks.
The U.S. Air Force has a contract with Mack Trucks for the four vehicles. Two would be refuse trucks and two would be dump trucks.
Aronsson, who lives in Hagerstown, said Volvo Powertrain North America has made a clear, strong commitment to Washington County.
"The biggest reason to stay is, naturally, the competence ...," he said. "That's not easy to renew in another place."