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High-Tech Vehicle Safety Systems
Electronic Stability Control
Drivers sometimes have to make a quick steering input in order to avoid a hazard. But, it's easy to steer too abruptly and cause the rear end of the vehicle to go into a spin, a situation automotive engineers call "oversteer". This is a particular problem when roads are slippery because of rain, snow or ice.
In such slick road conditions, reduced traction on the front wheels may also result in the vehicle not turning a corner as quickly as the driver intends. The vehicle then plows ahead, going on a much straighter path than required, a condition termed "understeer".
In either case, the result can be complete loss of control so that the vehicle runs off the road into the ditch, rolls over, or travels across the roadway centreline into the path of oncoming vehicles. These and other similar undesirable situations can potentially result in a collision and consequent occupant injury.
Electronic stability control systems selectively apply the vehicle's brakes and/or reduce the engine power to keep the vehicle moving in the desired direction and so prevent loss of control.
How do they work?
Many modern vehicles are equipped with anti-lock brakes. These systems have sensors that monitor wheel rotation and determine if a particular wheel is going to lock up. Valves in the braking system then reduce the braking pressure on the wheel in question, preventing wheel lockup, and providing optimal braking. ESC makes use of the same technology, with some additional sensing and control systems, but actually applies the brakes on one of the vehicle's wheels in order to counteract any tendency for the vehicle to spin out of control.
A range of vehicle sensors monitor steering inputs, throttle and brake application, the vehicle's lateral acceleration, rotation, and the individual wheel speeds. An on-board microprocessor integrates all of the data and determines if the vehicle is not going to travel in the direction intended by the driver. In this case, the system will apply the brake on one of the wheels and/or reduce engine power as needed to help correct understeer or oversteer.
The concept of applying a single brake to develop a restoring moment and thus counteract vehicle rotation is somewhat difficult for the lay person to grasp. Consequently, a physical analogy, involving controlling the rotation of a large rectangular block by pulling on a rope tied to one corner of the block, is used to supplement the pictorial representation of ESC operation as shown in the figure.
Are there any risks?
ESC cannot improve on the available traction for the vehicle's tires and the prevailing road surface condition. It cannot change the laws of physics. If a driver tries to drive too fast around a curve in the road, or steers too violently, ESC cannot prevent loss of control and a possible crash. Drivers should not push the limits of the system since, if these are exceeded, a resulting collision may well occur at higher speed with increased crash severity and a risk of greater injury.
Electronic stability control or ESC is generic terminology for the technology. Different vehicle manufacturers use different names and different acronyms for essentially the same systems. These include: Electronic Stability Program (ESP), Vehicle Stability Control (VSC), Vehicle Stability Assist (VSA), Dynamic Stability Control (DSC), StabiliTrak, AdvanceTrac and many other similar terms.
What can science tell us?
The Effectiveness of Electronic Stability Control in Reducing Real-World Crashes: A Literature Review; Susan Ferguson; Traffic Injury Prevention; Volume 8, Issue 4; pp. 329-338; December 2007 This paper reviews a number of studies that examined the real-world effectiveness of ESC. The majority of studies found that ESC is highly effective in reducing single-vehicle crashes; however, there was little or no effect for ESC in crashes involving multiple vehicles. Reductions in fatal, single-vehicle crashes were estimated as 30-50% for cars and 50-70% for sport utility vehicles. Fatal rollover crashes were about 70-90% lower with ESC regardless of vehicle type.Esc Secret (498 downloads) ; Christina M. Rudin-Brown and Peter C. Burns; Proc. CMRSC-XVII; Montreal, Quebec; June 3-6 2007
Despite the enormous safety benefits potentially afforded by ESC, there is a general lack of awareness about the technology among Canadian road users. Sixty percent of drivers had never heard of ESC, and less than 5% had vehicles with ESC. This paper discusses the reasons for the low rate of awareness and the implications this has for road safety. It also recommends strategies for promoting awareness and demand for ESC, and accelerating the availability of ESC. (104 KB PDF, 12 pages, 8 references)
- Electronic Stability Control (Transport Canada)
- Transport Canada Releases New Video on... ESC
- Electronic stability control (Wikipedia)
- Electronic stability control (IIHS)
- Electronic Stability Control (Transport Accident Commission, Victoria, Australia)
- ESC is a very effective technology for preventing loss of vehicle control
- One of the vehicle's brakes is applied automatically and/or engine power reduced if the vehicle is going into a spin
- The system can't change the laws of physics so drivers must still exercise caution
- Different manufacturers use a variety of different names and acronyms for the same technology
- ESC is required to be installed on all passenger cars, multi-purpose vehicles, trucks and buses with a Gross Vehicle Weight Rating of 4536 kg or less, and manufactured on or after September 1st, 2011