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Traction Control


 


What is Traction Control?

How Traction Control Works
Agency: Toyota New Zealand

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Traction Control Fact Sheet


What is traction control?
When would traction control be useful?
How does traction control work?
How effective is traction control?
Does traction control have limitations?
How common is traction control on today’s roads?

What is traction control?

Traction control is an active vehicle safety feature designed to help vehicles make effective use of all the traction available on the road when accelerating on low-friction road surfaces. When a vehicle without traction control attempts to accelerate on a slippery surface like ice, snow, or loose gravel, the wheels are liable to slip. The result of wheel slip is that the tires spin quickly on the surface of the road without gaining any actual grip, so the vehicle does not accelerate. Traction control activates when it senses that the wheels may slip, helping drivers make the most of the traction that is available on the road surface.
It is important to remember that traction control cannot create traction where there is none. On a truly frictionless surface (e.g., ice), vehicles with traction control would perform just as poorly as vehicles without it.

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When would traction control be useful?

Traction control is used to help drivers accelerate on slippery or low-friction conditions. These conditions include when roads are wet, icy, uneven, loose, or poorly maintained. Examples of when traction control would be beneficial include the following:

  • When accelerating up a hill where the surface is loose and gravelly.
  • Hitting a patch of slushy road that causes the vehicle to slow down as the wheels lose traction.
  • Accelerating at a green light on an icy road with traffic approaching from behind.

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How does traction control work?

Traction control works similarly to anti-lock braking systems (ABS) and is often considered as a supplement to existing ABS setups. In fact, traction control uses the same components as ABS:

  • wheel speed sensors that monitor the speed of rotation of the front or all four wheels;
  • a hydraulic modulator that pumps the brakes, and;
  • an electronic control unit (ECU)that receives information from the wheel speed sensors and, when necessary, directs the hydraulic modulator to pump the brakes.

Modern ABS and traction control systems are setup with the ECU and the hydraulic modulator attached together so that while they have different functions, they are physically one unit. The ECU continually checks whether some wheels are spinning faster than others - an indicator that the wheel is losing traction. When possible wheel slippage is detected, the ECU directs the hydraulic modulator to apply and release the brake in rapid succession ("pump the brake") to the problem wheel to reduce the speed of its rotation. Some traction control systems also reduce engine power to wheels that are about to slip. Once the wheel has regained traction, the system returns to monitoring wheel speed and comparing the rotational speed of the vehicle’s wheels.

Image courtesy of Toyota Canada

In a vehicle that uses reduced engine power to control the rotation of slipping wheels, drivers may experience a pulsation of the gas pedal when traction control is active. This pulsation is normal and is not an indication that something is wrong with the traction control system.

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How effective is traction control?

Tests have shown that traction control is effective for reducing wheel slip when accelerating in low-friction conditions (Song and Boo 2000), although this effect is more noticeable in four-wheel drive vehicles than in front-wheel drive vehicles. The same study found that traction control systems that incorporate reductions in engine power to slipping wheels are associated with better stability, but that brake-only systems are suitable for improving the acceleration performance of a vehicle (Song and Boo 2000).

Overall, the effectiveness of traction control to reduce or prevent crashes and injuries has not been well-documented. Nonetheless, due to its often being packaged together with ABS and electronic stability control (ESC), it is reasonable to suggest that driving a vehicle equipped with this trio significantly reduces fatal crash risk by up to 50%.

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Does traction control have limitations?

Yes. Like many other safety features, realizing the full benefits of traction control depends on whether or not drivers interact appropriately with it. This means continuing to drive safely and only in conditions where you feel safe driving. Behaviours like speeding, tailgating, and aggressive driving all work against the benefits of traction control. For example, driving too fast for the road conditions increases crash risk, even if your vehicle has traction control, since traction control is not designed to reduce stopping distance. Furthermore, whereas vehicles without traction control may experience a reduction in speed on slippery roads, the same speed reduction might not be observed in vehicles with traction control. As such, traction control might allow vehicles to reach a higher speed than is safe for the road conditions. Because of this, drivers must take extra care to monitor their speed.

It is always important to remain vigilant and focused on the driving task, no matter how many safety features are on the vehicle. Traction control does not help drivers stop faster in slippery conditions, so engaging in any behaviour that lengthens reaction time will have an adverse effect on overall safety. To illustrate, reaction time is increased by driver distraction, fatigue, and alcohol-impairment.

The good news is that the benefits of traction control can be accrued as long as drivers continue to use safe driving practices, caution, and good judgment.

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How common is traction control on today’s roads?

Traction control systems were first introduced on high-end vehicles in 1987, although some powerful rear-wheel drive vehicles in the early 70s were equipped with early version of traction control. In terms of current availability, traction control is generally available on any vehicle that has ABS since traction control was designed and built off existing ABS technology.

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