Because fewer drivers these days know how to work a stick and clutch pedal—or even care to—Mack Trucks Inc. says it is now seeing a 70% penetration rate for its mDRIVE 12-speed automated manual transmission (AMT), just one year after making the gearbox standard on its Pinnacle highway semitrucks.

Truckers are rapidly accepting automatics for their efficiency and ease of operation. “Growth of AMTs in the on-highway market is a story of vertical integration, fuel economy and drivers,” says Steve Tam, vice president of Columbus, Ind.-based analyst ACT Research Co. “The number of drivers who know how to drive a standard transmission is dwindling in an already difficult driver market.”

More truck makers are offering AMTs, which are about $5,000 more expensive than manuals but $5,000 cheaper than full automatics. Fully automatic gearbox makers, such as Allison Transmission, attempt to sell owners on a lower cost of ownership, but “many fleets don’t hold on to their trucks long enough to realize the benefit and are opting for the AMT instead,” Tam explains.

Mack says its mDRIVE gearbox delivers about 1.5% better fuel economy than a standard transmission. Earlier this year, it released a heavy-duty version that is now standard on its Graniteseries construction trucks.“There aren’t many vocational trucks out there that don’t have full automatics or, increasingly, AMTs,” Tam says.