Growing demand for automated mechanical transmissions in Mack and Volvo heavy trucks has caused Volvo Powertrain to plan assembly in the U.S. beginning in the third quarter of 2012.

It will spend $7 million to set up an assembly line, buy tooling, and train workers at its Hagerstown, Md., engine and transmission plant. The self-shifting transmissions are now produced at a Volvo Truck plant in Sweden. Versions are sold as Mack's mDrive and Volvo's I-Shift, and adapted to work with the two firms' engines.

Volvo Trucks North America introduced the I-Shift in 2007, and last year reached a penetration of 26 percent of sales. Customers continue to report significant fuel economy improvements from I-Shift, it said. Because it is only available with a Volvo engine, the transmission is helping to promote the company's integrated powertrain approach.

Mack said it introduced the mDrive early last year, and quickly sold out of the 500 units available. The mDrive's electronic controls are engineered to work with Mack Power diesels and is available on Pinnacle-model highway tractors.

The mDrive provides up to 1.5 percent improved fuel efficiency, better drivability, and enhanced driver satisfaction by automating gear shifting, while improving safety. Optional features such as Easy Shift provide especially smooth shifting in specialized applications like liquid bulk delivery and livestock hauling.