It's no doubt impressive when today's compact sedans -- which are loaded down with hundreds of pounds of safety gear and chassis reinforcements not found on vehicles from decades past -- top the 40 mpg mark. However, it's even more impressive when midsize sedans approach that mark as well.

You know about the compact 2011 Chevrolet Cruze and 2011 Hyundai Elantra which can hit 40+ mpg on the highway. Hyundai's 2011 Sonata midsize sedan can achieve 35 mpg on the highway in its base configuration. GM is now flaunting its 2012 LaCrosse which will come standard with eAssist technology (which will provide up to 37 mpg on the highway) and will be priced at roughly $30,000.

“It’s a very integrated powertrain system, with no compromises in driving performance, shift quality or ride and handling,” said Daryl Wilson, LaCrosse lead development engineer. “We believe this combination points to the future of vehicles powered primarily by an internal combustion engine.”

The LaCrosse will be powered by a traditional 2.4-liter direct injection four-cylinder engine which generates 180 hp. The engine is mated to a 6-speed automatic transmission. However, GM also includes its next generation "mild hybrid" system which it calls eAssist. On the LaCrosse, the eAssist electric motor provides an additional 15 hp and 79 pound-feet of torque during acceleration. Other features to improve fuel economy include an engine start/stop function and regenerative braking.

A 115V lithium-ion battery mounted in the trunk powers the electric motor, but it encroaches on cargo-hauling capabilities. Maximum cargo capacity drops from an already lackluster 13.3 cu ft to just 10.9 cu ft.

However, the benefits in fuel economy are huge. EPA ratings jump from 19/30 mpg (city/highway) to an impressive 25/37 mpg. The city rating falls short of Lincoln's MKZ Hybrid which pulls in an impressive 41 mpg, but that vehicle is priced higher at $35,180.

“The eAssist system is more than just the next-generation BAS system. The ability to integrate regenerative braking with the latest lithium-ion battery technology creates a system that delivers significant fuel-efficiency gains that customers will enjoy,” said Steve Poulos, global chief engineer of the eAssist system. “Being able to provide electric boost to the powertrain system during heavy acceleration and grade driving enables the LaCrosse transmission to operate more efficiently, while the added functionality of engine start-stop and fuel shut-off during deceleration provides added fuel savings.” 

Official pricing and availability of the Buick LaCrosse with eAssist should be available closer to its launch later next year.