SEATTLE (Money Magazine) - Car buyers place a lot of faith in new technology that's supposed to make driving safer. But even innovations that seem to work may have nasty unintended consequences.

Here are three -- all costly, all too new for much objective assessment -- that offer mixed blessings. Before you buy, make sure you're not placing yourself at risk.

Have you been blinded yet by bright, bluish beams heading toward you on the highway? High- intensity-discharge (HID) headlamps -- now available on luxury cars from Lincoln to Lexus, often as an option costing up to $900 -- deliver superior night vision for the driver, plus a cool high-tech look. But those brilliant beams can turn into a blinding glare for oncoming drivers or an uncomfortable distraction for the driver ahead when the lights reflect off a rear- or side-view mirror.

HID headlamps don't have a filament like regular bulbs. Instead they contain xenon gas, which emits light when zapped with electricity. The result: 50 percent more light than you'd get from halogen headlights, with no fading at the margins of the beam. They cost several times more than standard halogen lights, but the improved vision seems worth the cost, especially if you drive down a lot of dark, empty roads.

Yet safety may be in the eye of the beholder; many drivers believe that HID headlights are a menace in traffic. Although it's too early for statistics, when the National Highway Traffic Safety Administration (NHTSA) asked for public comment on these lights, it received complaints from more than 1,700 drivers who said they'd been momentarily blinded by oncoming HID lamps. Driving toward a car whose driver has been temporarily blinded can hardly be called safe.

Michael Flannagan, a perceptual psychologist at the University of Michigan's Transportation Research Institute, pinpoints the problem. "Headlamps are installed at a fixed angle," he says. "So when an HID-equipped car hits a pothole or goes uphill, as the car tilts, the lamps shine upward, flashing into the eyes of oncoming drivers. Road salt or grime on the lenses scatters the light more, aggravating the glare."

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Industry experts concede that HID glare can be annoying or distracting to others on the road but argue that it's not disabling. They tend to dismiss stories of drivers being blinded and say that those who are complaining are staring at HID lamps.

Martin Mainster, a physicist and retina specialist at the University of Kansas Medical Center, disagrees. "It's simple physics: The more light there is, the higher the potential for glare," he says. "But if you ask which takes longer to recover from, being flashed by HID headlights or by halogen headlights, the statistical research hasn't been done yet."

If you're faced with HID lights, suggests Stephanie Faul, spokeswoman for the AAA Foundation for Traffic Safety, use the same technique you'd employ if an oncoming driver left his or her brights on: Look away from the path of the headlights. But Faul adds that you need to be able to look at least 200 yards ahead to see where you're going.

Eventually, new technology will improve and refine HID lamps. NHTSA may eventually recommend that HID lights be weakened somewhat, just as the agency did with air bags. In the meantime, some luxury brands, such as Mercedes-Benz, already have computer-controlled load leveling to adjust the angle of headlight beams if there is extra weight in the back seat. In the future, predicts Flannagan, adaptive lighting will automatically alter headlamp angle and direction according to road conditions. Until then, if you spend much of your time in traffic, you should probably not bother buying HID headlights.

The obvious danger of driving with one hand holding or dialing a phone led New York State to emulate several European countries and ban the use of handheld phones while driving. Many other states are considering such laws. But that risk was supposed to have been eliminated by the introduction of dashboard cradles that made your cell phone work like a speaker phone or, in new cars, by sophisticated voice-activated systems integrated into the car's telematics. So now using a cell phone in a car is safe, right?

Not so fast. There's strong evidence that the problem with using a cell phone while driving is not just where your hands are, it's also where your head is.

When psychology researchers, in a 2000 experiment in Spain, asked people to drive while doing simple mental tasks like repeating letters of the alphabet, they found that even basic cognitive tasks caused drivers to pay far less attention to the road. And researchers at Pittsburgh's Carnegie Mellon University used magnetic resonance imaging to show that while the brain can learn to handle several tasks simultaneously, each task is allotted diminished brainpower. So if you're driving and phoning, you're probably not doing either particularly well.

"Driving is much more cognitively and mentally demanding than most people realize," said Marcel Just, co-director of Carnegie Mellon's Center for Cognitive Brain Imaging, in an interview last year. So what should you do with your hands-free phone? Save it for brief and urgent communication--or, if you must make important calls, don't be deluded into thinking that a hands-free phone makes it perfectly safe.

When SUVs first became popular, it seemed amazing that such huge cars accommodated only five or six people. Enter the third-row seat, which made it possible for SUV moms to carpool practically the entire soccer team.

Now a major selling point, third rows offer the option of seating your kids far away from the well-known dangers of the front seat. But dangers lurk in the back -- especially when you realize that one out of every five collisions involves a rear impact.

In a rear collision, third seats present a hazard that's never been measured. The issue, explains Gerald Donaldson, senior research director of Advocates for Highway and Auto Safety, is what is graphically known as "flail distance" -- the distance from the back of the third row to the tailgate. In an SUV, that can be as little as a few inches. If a rear seat collapses backward in a rear collision, it takes about three feet to lay down fully. (To get an SUV with three feet of flail distance, you're talking Suburban-size.)

"Obviously, if you're rear-ended at high speed, it's not good for anyone in the third row," says NHTSA spokesman Tim Hurd. "But since third-row seats are relatively new, we don't yet have enough data to analyze." In response to calls for beefed-up rear-impact safety standards, NHTSA will start gathering public and industry opinion this summer.