Their owners clearly have no concern for the environment, and I am prepared to shoot them a disdainful glance.
My sanctimony has the support of the Environmental Protection Agency, which rates the latest Fit and Mazda 2 at a maximum of 35 miles per gallon on the highway. The more commodious LaCrosse I am driving is rated at 36 m.p.g.
The 2012 edition of the 4-cylinder LaCrosse — an engine choice added in the 2011 model year — is able to achieve such a number because of a new system, called eAssist, that is now standard with the 2.4-liter, 182-horsepower engine. The new technology has bumped the fuel economy rating to 25 m.p.g. in the city, from 19 for last year’s car, and to 36 m.p.g. on the highway, from 30.
At the core of eAssist is a small electric motor. While General Motors and the E.P.A. consider this LaCrosse a hybrid, some would scoff because its electric motor is so small. It is rated at 15 horsepower, compared with 106 horses for the electric motor in the 2012 Lincoln MKZ Hybrid, a direct competitor.
Some might even consider the eAssist’s belt-driven “motor-generator” to be largely decorative. But Buick uses it as a cost-effective enabler, replacing sheer electric power with cleverness, allowing a tweak here and a tweak there, all adding up to the gain in fuel economy.
One tweak is cutting off fuel when the vehicle is coming to a stop, said Daryl Wilson, the lead development engineer for the LaCrosse. Such a fuel cutoff strategy is now widely employed on General Motors vehicles, but eAssist lets it to be used more aggressively, Mr. Wilson said.
“You will have the fuel cut to the engine as soon as your foot comes off the gas, and as long as your foot is on the brake, all the way down to zero speed,” he said. As that happens, eAssist uses the electric motor to smooth out “unpleasant torque disruptions that can happen during downshifts,” he said.
Buick also changed the final-drive ratio (to 2:64 from 3:23), which lets the engine operate at a lower speed on the highway, improving fuel economy. Normally an automaker would be reluctant to do that, because acceleration would be so leisurely, Mr. Wilson said. But the slight boost from the electric motor provides an offset.
The LaCrosse has an auto-stop feature typical of hybrids. When the car comes to a halt, the engine shuts off. Releasing the brake starts it again. The car also gets some aerodynamic improvements and low-rolling-resistance tires.
Despite adding lithium batteries and other eAssist components, Buick has kept the unloaded weight (4,026 pounds on my test car) virtually unchanged. Mr. Wilson says that was possible through a strategy that ranged from replacing the previous steel wheels with aluminum wheels to reducing the gas tank to 15.8 gallons, from 18.4. The driving range has not changed, Mr. Wilson said, because of the improved fuel economy.
During about 500 miles of highway cruising at speeds between 65 and 75 m.p.h., my mileage ranged from 31.6 m.p.g. to 34 m.p.g. It didn’t help that winds were strong enough that the Thruway posted a wind advisory.
Earlier in the day — working my way across the Green Mountains of Vermont on two-lane roads — there was no sense of a lack of power. That is partly because the eAssist gets its own assist from a smart, quick-to-react 6-speed automatic transmission.
The LaCrosse also seemed more willing than many front-wheel-drive vehicles to head into a turn. And while the ride remains comfortable, the body lean is appropriately controlled for a sedan with luxury aspirations. If there’s a dynamic fault it is the steering: while predictable and accurate, it communicates little feedback from the road.
One downside for the new LaCrosse is less cargo capacity — 11.7 cubic feet versus 13.3 for the previous car or the V-6 model — because some trunk space was given over to the eAssist’s lithium-ion battery pack. Both figures are small for a midsize car, although comparable with the Lincoln MKZ Hybrid.
One thing missing on the LaCrosse is a badge proclaiming the presence of eAssist. A bystander cannot readily tell the fuel-sipping version from the thirstier LaCrosse with a 3.6-liter V-6.
“We are selling the Buick LaCrosse here,” Mr. Wilson, the Buick engineer, said. “We are not trying to sell this new gizmo in the Buick LaCrosse.”
In fact, in what could be an effort to eliminate class warfare, there are no longer any badges showing the different trim levels.
The pricing on the LaCrosse is also competitive. The Lincoln MKZ Hybrid matches the Buick’s highway mileage and carries a superior city rating (41 m.p.g.). It starts at $35,650. If you added the options needed to match my well-equipped $38,173 LaCrosse test car, the comparable Lincoln would be $41,000.
The LaCrosse with a V-6 starts at $31,290, but in return for its 303 horsepower the mileage rating drops to 17 city, 27 highway. While the V-6 LaCrosse is offered with all-wheel drive, the eAssist version is front-drive only.
A similar eAssist system will be used in the 2013 Chevrolet Malibu ECO, which is expected to carry a rating of 26 m.p.g. city and 38 m.p.g. highway.
While only the most generous person (outside G.M.) would consider the LaCrosse eAssist to be a hybrid, it does appear to be a success. Buick has retained the things that make the LaCrosse a comfortable, quiet and soothing sedan, and it has managed to improve the car’s fuel economy without any sense of sacrifice.”