If you've checked your e-mail in the last year or so, then you've no doubt read the cautionary tale about a woman who hydroplaned while using cruise control during a rainstorm. And you probably read it as skeptically as you read everything that lands unsolicited in your mailbox.

"We've received many phone calls and e-mails from members asking about this particular story," says Frank Niland of the Club's Traffic Safety Services department. "And a lot of people are really worried about what they read. They all want to know, should I use cruise control in the rain or not?"

Of course, safety experts can't say for certain whether the events described in the e-mail actually happened or whether they're just another urban legend making the rounds in cyberspace. But experts can say that the story contains some sound advice about wet-weather driving. And even the tale's more questionable details point to useful but little-known facts about hydroplaning--facts that could save your life.

Fact or Fiction?

Just to refresh your memory, the story runs something like this: On a rainy night, a woman was driving with her cruise control engaged when her car hydroplaned. The tires lost contact with the pavement, and her vehicle accelerated dramatically-- "took off like an airplane" or "literally flew through the air," depending on the version you read. Although the car was totaled, the driver escaped serious injury. A highway patrolman arriving at the scene told the badly shaken woman never to use cruise control on wet or icy pavement. He estimated that the car ended up traveling 10 or 15 mph faster at the time of the collision than the speed set on the cruise control.

Could the tires have really lost contact with pavement, as the e-mail says?

In fact, that's the textbook definition of hydroplaning: a layer of water gets between the rubber and the road. Ordinarily, the treads channel accumulated water out from under the tire to improve traction. But in heavy rain or at high speeds, the treads can't remove water fast enough. "Any car will hydroplane if you're going too fast or the water is too deep," says Bob Toth, marketing manager at Goodyear. Essentially, your tires skim along on a film of compressed water.

Could the car accelerate, or "take off like an airplane," under such conditions? Not likely. Since the tires are off the pavement, they don't have enough traction to accelerate, and only the vehicle's inertia can carry it along. But you might think you're going faster. "It involves the perception of speed," says Niland. "It seems as though you're going faster when you hydroplane, even though you're not traveling any faster than you normally would."

Should you turn off the cruise control in the rain? Absolutely. Nearly every carmaker includes warnings about cruise control (a.k.a. "speed control") in their owner's manuals. For example, Toyota notes, "To help maintain maximum control of your vehicle, do not use the cruise control when driving in heavy or varying traffic or on slippery (rainy, icy, or snow-covered) or winding roads." In fact, on some upscale cars, safety features lock out cruise control when you have the windshield wipers on high.

The Perils of Cruise Control

Using cruise control always carries three inherent dangers. "It may lead to loss of attention," says Niland. "It lessens your ability to adjust your speed quickly--simply by lifting your foot off the accelerator, for example. And it can cause a skid if you're on a slick surface."

That advice goes for cars with traction control, too. These systems sense loss of traction on the drive wheels and restore traction by selectively applying the anti-lock brakes or reducing engine power. "Traction control systems make a big difference on wet roads," says Niland. "But you can't rely on them to prevent hydroplaning. You still shouldn't use cruise control in the rain, even if your car is equipped with traction control."

Essentially, concludes Niland, "cruise control is intended only for a situation where you can maintain a constant rate of speed." That means relatively open highways in dry weather. Urban legend or not, the story circulating around the Internet has a moral that you can take to heart.