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Status Report, Vol. 41, No. 5 | June 13, 2006 Subscribe

ESC reduces multiple-vehicle crashes as well as single-vehicle ones

Electronic stability control (ESC) could prevent nearly one-third of all fatal crashes and reduce the risk of rolling over by as much as 80 percent. The benefits are found in crashes involving one vehicle and more than one.

An extension of antilock brake technology, ESC is designed to help drivers retain control of their vehicles during high-speed maneuvers or on slippery roads. A previous Institute study found significant effects of ESC in reducing fatal single-vehicle crash risk. Using data from an additional year of crashes and a larger set of vehicle models, the researchers have updated the 2004 results, finding that ESC reduces fatal multiple-vehicle crash risk by 32 percent.

This research confirms that ESC reduces the risk of all single-vehicle crashes by more than 40 percent — fatal ones by 56 percent. The researchers estimate that if all vehicles were equipped with ESC, as many as 10,000 fatal crashes could be avoided each year.

"The findings indicate that ESC should be standard on all vehicles," says Susan Ferguson, Institute senior vice president for research. "Very few safety technologies show this kind of large effect in reducing crash deaths."

Availability varies

ESC is standard on 40 percent of 2006 passenger vehicle models and optional on another 15 percent. It's standard on every 2006 Audi, BMW, Infiniti, Mercedes, and Porsche. Another eight vehicle makes (Cadillac, Jaguar, Land Rover, Lexus, Mini, Toyota, Volkswagen, and Volvo) offer at least optional ESC on all of their models. But ESC, standard or optional, is limited to 25 percent or fewer models from Chevrolet, Dodge, Ford, Hummer, Mazda, Mitsubishi, Saturn, Subaru, and Suzuki.

After studies in 2004 by the Institute and the National Highway Traffic Safety Administration, some manufacturers announced plans to make ESC standard on all SUVs, and the percentage of SUV models with standard ESC has been growing faster than for cars.

As a stand-alone option, ESC costs from about $300 to $800, but it can cost more than $2,000 on some models when packaged with other equipment. A potential problem for increasing consumer awareness is that automakers market ESC by various names including Electronic Stability Program, Stabili-Track, or Active Handling.

"When ESC is optional, this hodgepodge of terms is bound to be confusing," Ferguson points out. "It's good that some of the major manufacturers have pledged to make ESC standard on their SUVs in the next few model years, and it should be standard on cars and pickup trucks too."

How ESC works

Antilock brakes have speed sensors and independent braking capability. ESC adds sensors that continuously monitor how well a vehicle is responding to a driver's steering wheel input. These sensors can detect when a driver is about to lose control because the vehicle is straying from the intended line of travel — a problem that usually occurs in high-speed maneuvers or on slippery roads. In these circumstances, ESC brakes individual wheels automatically to keep the vehicle under control.

When a driver makes a sudden emergency maneuver or, for example, enters a curve too fast, the vehicle may spin out of control. Then ESC's automatic braking is applied and in some cases throttle reduced to help keep the vehicle under control.

ESC is relatively new. Only in the last few years have researchers had sufficient data to analyze its effects on real-world crashes. The new Institute study is based on data from the federal Fatality Analysis Reporting System and police reports of crashes in 10 states during 2001-04. Researchers compared crash rates for cars and SUVs without ESC and the same models in subsequent years when ESC was standard (note: some vehicles with optional ESC were included in the no-ESC group because so few buyers choose this option).

More effects of ESC on SUVs

The data in the Institute's 2004 study weren't extensive enough to allow researchers to compute separate risk reduction estimates for cars and SUVs. However, this was possible in the broader analysis that's just completed. While both cars and SUVs benefit from ESC, the reduction in the risk of single-vehicle crashes was significantly greater for SUVs — 49 percent versus 33 percent for cars. The reduction in fatal single-vehicle crashes wasn't significantly different for SUVs (59 percent) than for cars (53 percent).

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 of SUVs by 80 percent, 77 percent for cars.

ESC was found to reduce the risk of all kinds of fatal crashes by 43 percent. This is more than the 34 percent reduction reported in 2004. If all vehicles had ESC, it could prevent as many as 10,000 of the 34,000 fatal passenger vehicle crashes that occur each year.

Insurance claims show effects on collision losses

The results of the Institute's studies showing significant reductions in serious crash risk are reflected in some insurance losses. According to a new analysis by the Highway Loss Data Institute, an affiliate of the Insurance Institute for Highway Safety, losses under collision coverage are about 15 percent lower for vehicles with ESC than for predecessor models without it. However, ESC doesn't have much effect on property damage liability claims or the frequency of injury claims. These findings track police-reported crashes, which show little effect of ESC on the risk of low-severity multiple-vehicle crashes.

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