This LaCrosse just glided through the hills and country roads around Milford — home to GM's proving grounds — where I test drove it.

There were a few times, if you really stepped on the gas, that the engine whined a little bit, a product of GM's 2.4-liter four-cylinder engine needing just a bit more power than its 182 horses available. But those were the extreme conditions — for the most part it just kept chugging along. On the highway, the LaCrosse felt at home around 80 mph. (It's unlikely it will get 37 mpg at that speed, but I was just keeping up with traffic.)

The steering feels crisp and firm and the suspension falls to the soft-but-firm side of a ride. But, again, there's nothing wrong with that in this car, which is by no means a race car. If gas is at $4 a gallon, you could drive this car to Chicago for around $32, which is still a couple of billion dollars cheaper than a high-speed rail ticket. And the LaCrosse could get you there in five hours — the super-train will take five decades.

The ride is likely quieter, too. Engineers improved its aerodynamics by adding a number of panels under the body. Cutting wind resistance also cuts noise.

That's the funny thing about this Buick. I asked if engineers could break down point by point how each improvement increases fuel economy. Does the EPA's improve things 6 percent, the electric motor 12 percent and the aero 4 percent? But, really, it doesn't work that way.

If the air resistance is lower, the engine doesn't stress as much, so the battery can hold its charge longer and the electric motor can kick in a little less from time to time. But the electric steering draws power from the batteries but also eliminates parasitic engine losses at the same time. Each improvement impacts a number of areas, which in turn can pay it forward at the pump.

The sum of the 2012 LaCrosse is truly greater than its pieces.