Electronic Stability Control

Electronic Stability Control (ESC) is an advanced vehicle safety technology aimed at preventing crashes. Several studies have found that ESC is very effective at reducing crash and fatality rates by helping drivers maintain control of their vehicles.

NRMA's position

• NRMA encourages vehicle manufacturers to fit ESC as a standard feature.
• NRMA encourages private and fleet car buyers to specify a vehicle equipped with ESC.
• NRMA calls on vehicle manufacturers to adopt a common name to refer to the technology to avoid consumer confusion with the product.

Findings of International research into ESC

IIHS study
The US based Insurance Institute of Highway Safety (IIHS) studied the effectiveness of stability control as a road safety measure. The study, released in October 2004, found that the fitment of ESC was effective in reducing single vehicle crashes including those involving fatalities. The US study showed that based on all police-reported crashes in seven states over two years, ESC was effective in reducing fatal crashes by 34 per cent.

Swedish study
A Swedish National Road Administration study in 2003 reported ESC effectiveness levels in different conditions on Swedish roads. It found that the effectiveness of ESC in reducing crashes was around 22 per cent. In wet and snow conditions the reductions attributed to ESC were even higher.

DaimlerChrysler
DaimlerChyrsler claims that "The average share of newly registered Mercedes models involved in such (single vehicle) accidents in 1998/1999 was 20.7 per cent. ESP® (ESC) helped to reduce this figure by more than 42 per cent in 2002/2003. At the same time, the share of passenger car models from other brands involved in these types of traffic accident fell by only about 13 per cent."

The IIHS study found that ESC benefits are most prevalent in single vehicle crashes. Examples of single vehicle crashes include roll-overs and impacts with rigid objects such as trees. In Australia, single vehicle crashes accounted for 399 fatalities in 2003 (44 per cent of total fatalities), more than the number of fatalities from multiple vehicle crashes.

How stability control works

Components
ESC builds on the ABS brakes and traction control components already installed into a vehicle. It uses the wheel speed sensors and the ability to apply brake pressure to individual wheels but adds steering angle and vehicle direction sensors. Some more advanced systems also have body roll sensors.

Function
ESC continuously compares the driver's steering wheel position to the direction of travel of the vehicle. When the control unit detects a difference, ESC operates by independently applying the brakes to individual wheels. In some cases, it will reduce the engine power as well. ESC helps the driver to maintain control of the vehicle.

Some ESC systems will intervene sooner than others. Other vehicles are fitted with switches so the driver can switch the system off.

When do you lose control?
ESC starts to intervene when the vehicle travels on a different track to that intended by the driver. This typically occurs when a driver tries to take a corner too fast or swerves to avoid an obstacle. The vehicle may then understeer or oversteer.

Understeer is when the front wheels start to slide sideways in a corner and the vehicle does not turn as sharply as the driver intended. This occurs because the front wheels have lost traction with the road. Oversteer is the opposite - it occurs when the rear wheels lose traction in a corner and the vehicle turns more than the driver intended. See Figure 1 for a graphical representation. In Figure 2 the two situations are compared and how ESC applies the brakes to help the driver maintain control is shown.

What is the difference between ESC, ABS and traction control?

Where ABS and traction control are effective in assisting with braking and acceleration, the addition of the extra sensors enables ESC to offer the driver assistance in turning under hazardous conditions. As road safety measures go, ABS has not proven to be as effective a measure in preventing crashes. Many reports on the real world performance of ABS brakes have found that vehicles equipped with ABS had a higher risk of involvement in single vehicle crashes, probably because of driver over-confidence. Vehicles equipped with ESC also feature traction control and ABS brakes.

Vehicle equipment	Situation
Traction control	This systems prevents wheel spin under acceleration, which helps to maintain vehicle stability when accelerating.
ABS - Anti-lock Braking System	ABS prevents wheels locking during heavy braking. This helps a driver steer while braking heavily and achieves shorter braking distances on slippery surfaces.
EBD - Electronic Brake-force Distribution	Helps to balance braking forces between front and rear. In turn this helps to minimise braking distance and keep stability under light axle loads.
ESC - Electronic Stability Control	Builds on all the functions above but adds the ability to control loss of traction during cornering as well.

Other names for ESC

ESC has a wide variety of marketing names used by different vehicle manufacturers for what is essentially the same function, which is potentially confusing for consumers. ESC names include:

• Electronic stability program (ESP)
• Vehicle stability control (VSC)
• Dynamic stability control (DSC)
• Vehicle stability assist (VSA)

By NRMA Motoring, October 2007.