ELECTRONIC STABILITY CONTROL



1. What is electronic stability control (ESC)?

ESC is a vehicle control system comprised of sensors and a microcomputer that continuously monitors how well a vehicle responds to a driver's steering input. It selectively applies the vehicle brakes, and modulates engine power to keep the vehicle traveling along the path indicated by the steering wheel position. This technology helps prevent the sideways skidding and loss of control that can lead to rollovers. It can help drivers maintain control during emergency maneuvers when their vehicles otherwise might spin out. The systems are marketed under various names including dynamic stability control, vehicle stability control, and dynamic stability and traction control among others.

2. How does ESC help drivers maintain control?

A driver loses control when the vehicle goes in a direction different from the one the steering wheel position indicates. This typically occurs when a driver tries to turn very hard or turn on a slippery road. Then the vehicle may understeer or oversteer. When it oversteers it turns more than the driver intended because the rear end is spinning or sliding out. When a vehicle understeers it turns less than the driver intended and continues in a forward direction because the front wheels have insufficient traction. ESC can prevent under and oversteer by selectively braking wheels to produce a counteracting force which helps correct the vehicle's direction of travel. In some cases engine throttle also is reduced.

3. How effective is ESC in preventing crashes?

In Institute studies, ESC has been found to reduce fatal single vehicle crash risk by 49 percent and fatal multiple vehicle crash risk by 20 percent for cars and SUVs. Many single vehicle crashes involve rolling over, and ESC effectiveness in preventing rollovers is even more dramatic. It reduces the risk of fatal single vehicle rollovers by 75 percent for SUVs and by 72 percent for cars.

Federal studies also show large benefits. The National Highway Traffic Safety Administration (NHTSA) estimates the installation of ESC reduces single vehicle crashes of cars by 26 percent and single vehicle crashes of SUVs by 48 percent. NHTSA estimates that ESC has the potential to prevent 64 percent of the car rollovers and 85 percent of the SUV rollovers that would otherwise occur in single vehicle crashes.

ESC is available on some large trucks and has great potential to prevent rollover crashes, however, the benefits of ESC for these vehicles haven't been evaluated.

4. Does ESC activate in typical everyday driving?

For most drivers ESC isn't likely to activate frequently. It won't prevent most of the fender bender crashes that occur so often in stop and go traffic, for example. It's designed to help a driver in the relatively rare event of loss of control at high speed or on a slippery road.

5. Does the government require ESC?

A federal rule will require ESC in all cars, SUVs, pickups, and minivans by the 2012 model year. Under the final rule NHTSA issued in April 2007, 55 percent of 2009 models, 75 percent of 2010 models, 95 percent of 2011 models, and 100 percent of 2012 models must have ESC. Passenger vehicles must have ESC to be eligible for a TOP SAFETY PICK award from the Institute.

6. Are ESC systems widely available?

Germany's Robert Bosch GmbH was the first supplier to bring ESC to market on the 1995 Mercedes-Benz S-Class in Europe. The technology made its way to the American market a few years later as optional equipment on luxury cars. By the 2001 model year it was standard on a number of high selling vehicles and available as an option on many more. Since then automakers have been putting ESC on their vehicles, particularly SUVs, at a steady rate. The percentage of vehicles with this technology has increased tenfold since the 1998 model year. For the 2011 model year ESC is standard on 90 percent of cars, 100 percent of SUVs, and 72 percent of pickups.

7. Can ESC help reduce insurance losses?

Yes. Losses under collision coverage are about 15 percent lower for vehicles with ESC than for predecessor models without it according to an analysis by the Highway Loss Data Institute. ESC doesn't have much effect on liability claims filed when an at-fault driver damages someone else's car or property or the frequency of personal injury claims filed to cover medical expenses.



Depending on conditions such as vehicle speed and terrain, Variable Ride-Height Suspension (VRHS) raises or lowers the ride height of the vehicle while it is in motion. Some VRHS systems operate automatically, while others require the driver to select the appropriate mode. VRHS systems can have a favorable effect on a vehicle's likelihood to roll over because they lower the height of the vehicle's center of gravity and improve its Static Stability Factor (SSF) rating for highway driving. Illustration: www.safercar.gov