Hyundai's entry into the hybrid segment seems a simple enough formula: Stick a hybrid powertrain into its redesigned and widely praised Sonata family sedan, make sure it achieves 40 mpg on the highway, and sit back and count sales. With the 2011 Hyundai Sonata Hybrid, the Korean automaker signals that it not only intends to compete in the hybrid category, but win it as well.

On most counts, the Hyundai formula delivers. As with the regular Sonata, the Sonata Hybrid is distinctively styled, roomy and stacked with a lot of creature comforts as standard equipment. Add 36 mpg around town and 40 mpg on the highway and it's clear that the Sonata Hybrid takes aim at top contenders in the segment that include hybrid versions of the Ford Fusion, Nissan Altima and Toyota Camry.

The Sonata Hybrid varies from its competition in its powertrain, which is designed in-house and essentially uses a separate electric motor sandwiched between the 2.4-liter gasoline engine and traditional six-speed automatic transmission. Its lithium-polymer battery pack also differs from the competition's nickel-metal hydride batteries, as Hyundai says it's more space-efficient and better at resisting thermal damage caused by constant charging and discharging.

On paper, the Sonata Hybrid seems like a winner. Yet its performance ultimately isn't quite as refined as the hybrids from Ford, Nissan and Toyota. The Sonata Hybrid's powertrain and braking fight to sync their computers with the driver's intentions, and the result is an often clumsy, jerking response during low-speed driving in moderate traffic. This isn't enough to keep the Sonata Hybrid off our list, but it does make it worth investigating the competition -- or even just a regular Sonata -- a little more closely.

The 2011 Hyundai Sonata Hybrid is a midsize family sedan available in one well-appointed trim level. Standard equipment includes 16-inch alloy wheels, keyless ignition/entry, dual-zone automatic climate control, cruise control, full power accessories, heated and folding outside mirrors, automatic headlights, a tilt-and-telescoping steering column, an auto-dimming rearview mirror, an eight-way power driver seat, a trip computer, Bluetooth and a six-speaker audio system with CD player, satellite radio, an iPod adapter and an auxiliary audio jack.

The sole option package adds 17-inch alloy wheels, a touchscreen navigation system, a rearview camera, a panoramic sunroof, leather upholstery, heated front and rear seats, and a premium nine-speaker Infinity audio system with HD radio.

The 2011 Hyundai Sonata Hybrid is powered by a 2.4-liter four-cylinder gasoline engine generating 166 horsepower and 154 pound-feet of torque, paired with an electric motor making 40 hp and 151 lb-ft. Combined, the two power units are good for 206 peak hp and 193 lb-ft of torque. A six-speed automatic with manual shift control is the only available transmission.

In Edmunds performance testing, the Sonata Hybrid accelerated from zero to 60 mph in 8.7 seconds, which is reasonably quick for a hybrid. The EPA estimates Sonata Hybrid fuel economy at 36 mpg city/40 mpg highway and 38 combined. That's quite a bit better than the Camry Hybrid, though about the same as the Ford Fusion Hybrid.

Safety features on the 2011 Hyundai Sonata Hybrid include antilock brakes, traction control, stability control, front side-impact airbags, full-length side curtain airbags and active front head restraints.

In the government's new, more strenuous crash testing for 2011, the Sonata Hybrid earned a top five-star rating for overall crash protection, with four out of five stars given for front-impact protection and five stars for side-impact protection. In Insurance Institute for Highway Safety testing, the 2011 Hyundai Sonata earned a top rating of "Good" for frontal-offset, side-impact and roof-strength protection.

In Edmunds brake testing, the Sonata Hybrid came to a stop from 60 mph in 126 feet, an average result for the class. By comparison, the Fusion Hybrid makes the same stop in 122 feet.

A well-balanced chassis and suspension make the 2011 Hyundai Sonata Hybrid feel more agile than its family sedan intentions might suggest. The light-effort steering action feels lively yet still proves fairly precise. The hybrid powertrain's electric motor makes accelerating from a dead stop a smooth affair, and at highway cruising speeds the electric motor can aid quick bursts of acceleration that makes the engine almost feel turbocharged.

But in low-speed driving or quickly changing traffic conditions, the Sonata Hybrid shudders and lurches while deciding which gear it wants. It is similarly indecisive under braking, as the transition between electronic regenerative braking (which helps recharge the battery pack) and mechanical braking is clumsy and unpredictable. Almost all hybrids exhibit some quirkiness, but the Sonata Hybrid's acceleration and braking is the quirkiest of the bunch.

Like its conventional counterpart, the Sonata Hybrid features solid interior fit and finish, with tight panel gaps and subtle, futuristic appearance cues infused into the dash and center stack design. Knobs with precise action and detents control primary climate and radio settings, while in models equipped with navigation, a 7-inch touchscreen display handles most phone, map and audio functions.

And although the Sonata Hybrid sacrifices some interior and trunk volume to its battery pack -- about 6 cubic feet on both counts -- relative to the regular Sonata sedan, the rear seat is plenty roomy for two adults. Three can fit in a pinch. Passengers taller than 6 feet, however, may find that the sleek roof design infringes on their head space.