Image Gallery: Car Safety
Image Gallery: Car Safety

Image Gallery: Car Safety Cars spray water in downtown Auckland, New Zealand, as they drive through deep puddles during heavy rain.

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How Traction Control Works

Way back in the dark ages of the 1970s, cackling automotive engineers in white coats, black rubber gloves, and goggles with flopping straps at the temples worked in deep, dark German basements to create anti-lock braking systems, or ABS. An array of sensors, computers and technological wizardry eliminated the need to pump the brakes. Once those sensors were in place, it was easy enough to make them do double-duty to keep the tires from chirping, smoking and slipping when the car accelerated, too. By 1985, some scientists of a less-mad variety had created traction control systems.

And now, traction control is widely available because it piggybacks on the vehicle's ABS -- which was required on all vehicles sold in the United States for the 2012 model year and beyond. And while it goes by many names and acronyms, they all mean the same thing: safer driving through traction control:

  • ETC or TC: Electronic Traction Control or just Traction Control
  • DSC: Dynamic Stability Control
  • DTC: Dynamic Traction Control
  • ESP: Electronic Stability Program

The Toyota Mark X is driven to demonstrate its VGRS safety system. VGRS, which stands for variable gear ratio steering, controls steering, braking and turning of the tires to reduce spinning and skidding when braking and turning on slippery surfaces.

AP Photo/Koji Sasahara

Where the Rubber Meets the Road … and the Electronic Sensors

The scientists behind the first traction control systems weren't completely mad. Actually, they were probably boringly task-oriented and striving to meet performance goals in some lovely corporate building with vacation time and benefits and nary a pair of black rubber gloves in sight. That's fine, engineers. Be that way. Readers will have to supply their own mad cackling while reading how traction control works.

So, living in the twenty-first century means that your car has a computer. It also means that your car probably uses a drive-by-wire system, which means there's no mechanical connection between the gas pedal and the throttle mechanism; pressing the accelerator pedal sends an electronic signal to the throttle, and it speeds up the car. And having ABS means that you have speed sensors at each wheel tracking how fast the wheel is turning; the computer compares all four wheel speeds to see if one of them isn't doing its job. In the case of ABS, it's making sure one of the wheels isn't locked up and sending you skidding into a ditch. With a traction control system, those same electronics make sure the wheels are all turning at the same speed compared to the road. It'll determine if a wheel is slipping -- you know, spinning faster than the other wheels, all wild and crazy-like. A cackle might work here, if you choose.

The car's computer has a couple of choices to make, and what it picks depends on how it was programmed and what the conditions are. Often, the computer will apply the brakes just a little bit to slow that out-of-control tire down until the tread can get some bite on the road and prevent it from slipping. If further steps are required, traction control can even reduce engine power and torque until the tire slows down enough to get a grip. A cackle here might be inappropriate.

This Lexus GS makes good use of complex engineering to keep the car straight and deliver a safe ride.

AP Photo/Koji Sasahara

When It Works … and When It Doesn't

What do you have to do to make this system work? That's the best part: not a dang thing. If that little warning light in the dashboard didn't come on, you'd probably never know the system was ever springing into action.

When the road is slippery, for whatever reason, that little light is likely to come on. Rain-slick roads, icy patches and even wet leaves can come between the grippy rubber of the tires and the nubbly surface of the road. When a tire catches an icy patch or loses traction in a deep puddle, the sensors know it, and the traction control system kicks in.

It also helps when you're accelerating from a stop. While your car isn't moving very fast in those situations, having your wheels spin can still cause you to lose control. Best case scenario: You look like a fool on the local news with your tires spinning at a red light during your city's annual Snowpocalypse. Worst case scenario: You spin off the road and into a ditch.

When you've got traction in all four tires and they're spinning at the same rate, your car is far more stable. And that's why insurance companies often give discounts for cars with ABS and traction control. Insurers love stability.

Even older model cars had a rudimentary traction control system. Ever see an old, rear-wheel-drive muscle car peel out of a parking lot? If the rear end swayed and fishtailed all over the place while the tires squealed and smoked, that car probably didn't have a limited-slip rear differential. A limited-slip rear differential keeps the car's two rear wheels (where the engine's power is going) turning at the same speed. Limited-slip rear differentials are still used in powerful rear-wheel-drive sports cars, but traction control is a much more sophisticated system that's used in all types of cars. Mash the pedal of a car with a 600-horsepower, V-12 engine in 2013, and the traction control system will make sure as much power as possible is translated directly into moving the car forward, with little (or no) loss of power in a fancy fishtailing maneuver.

A Chevrolet Camaro burns its tires alongside a Navy fighter jet during a demonstration on the flight deck of the USS Midway in San Diego, Calif.

AP Photo/Lenny Ignelzi

You Can't Control Me!

There are still some people who simply don't like cars telling them what to do. These drivers want to feel the road, control the brakes, chirp the tires and drive down the road listening to Boston's "Greatest Hits" album. Well, then you should know that track number six is "Cool the Engines," dude, so take a chill pill. But the dude does make a good point -- sometimes you do want to turn off traction control. In that case, it's usually as easy as pushing a button on the console, often somewhere near your left knee.

Why would you turn off something so helpful? Well, it's actually less helpful to have traction control when you've got a wheel stuck deep in snow or mud. In that case, you want the tire to spin, sending snow or mud flying out behind the car, until the tire finds some hard ground to grab onto. In that same situation, rocking the vehicle back and forth a bit can help you get unstuck, and traction control won't let you rock. Just ask that Boston-loving driver.

Some cars have a terrible reputation for this. The traction control system in a Toyota Prius is so sensitive that it'll brake hard in snow rather than fluttering the brakes to find traction. It allows no wheel spin and even shuts down power to the wheels. Consumer Affairs even called it "dangerous" [source: Cars Direct]. There are instructions on the Internet for turning the Prius traction control system off; that is, if you want to live on that edge. If you don't drive a Prius in blizzards very often, however, it's probably better to leave it on nearly all the time.

Speaking of people who have a love-hate relationship with traction control, let's talk about Formula One racing. When traction control was invented by Bosch in the 1980s, F1 was all over it. And then the electronics and telemetry got out of hand in the 1990s (look up Nigel Mansell and be amazed at his car) and Formula 1 banned traction control. But traction control uses so many of the same systems and sensors as other legal devices require that F1 officials simply couldn't tell who was cheating by using traction control. So in 2002, the gods of F1 allowed it once again. But the interval was short lived. Traction control was also part of launch control systems which F1 banned in 2004, and traction control itself eventually followed -- yet again -- by being banned for the second (and so far) final time in 2008.

Lots More Information

Author's Note: How Traction Control Works

I live in the Pacific Northwest, where the snow mostly stays in the mountains. The valleys get a lot of rain, but the roads are sloped and we have pretty good drainage in my town. But the leaves! The wet leaves every fall engage my traction control system every year. The gutters fill with leaves and block the grates in the street, leaving piles of sopping wet leaves floating in inches of water. If I dare to park at the curb, I'm guaranteed to spin the wheels a bit when I pull away. It's funny that it took me awhile to learn to live in harmony with ABS -- I wanted to pump my brakes so badly -- but I came to rely on traction control pretty quickly. Easy on the gas pedal, wait for the system to kick in and the gutter-side tires to catch and then ease on out of the parking space. Fall is really the only season that my traction control system is ever used.

Sources

  • Ask.Cars.com. "Do any cars come without ABS anymore?" Ask.Cars.com. May 3, 2011. (Sept. 2, 2013) http://ask.cars.com/2011/05/do-any-cars-come-without-abs-anymore.html
  • Cars Direct. "Advantages of Traction Control." CarsDirect.com. Jan. 27, 2012. (Aug. 21, 2013) http://www.carsdirect.com/car-safety/advantages-of-traction-control
  • Cars Direct. "How to Disable Prius Traction Control." CarsDirect.com. Jan. 27, 2012. (Aug. 21, 2013) http://www.carsdirect.com/car-safety/how-to-disable-prius-traction-control
  • DrivingFast.net. "Common Winter Driving Myths Busted." DrivingFast.net. (Aug. 21, 2013) http://www.drivingfast.net/road/winter-driving-myths.htm#.UiTe7Dash8F
  • Edmunds.com. "Traction Control." Edmunds.com. May 5, 2009. (Aug. 21, 2013) http://www.edmunds.com/car-safety/traction-control.html
  • Formula 1. "Traction control." Formula1.com. (Aug. 21, 2013) http://www.formula1.com/inside_f1/understanding_the_sport/5278.html
  • Magliozzi, Tom and Ray. "Why would anyone ever turn off traction control?" NWAutos.com. (Aug. 21, 2013) http://blog.nwautos.com/2010/10/why_would_anyone_ever_turn_off_traction_control.html
  • Tracy, David. "This Is How ABS, ESC, and Traction Control Work." Jalopnik.com. June 24, 2013. (Aug. 21, 2013) http://jalopnik.com/this-is-how-abs-esc-and-traction-control-work-513807036