The Effectiveness of Esc (electronic Stability Control) in Reducing Real Life Crashes and Injuries

ESC (Electronic Stability Control) was introduced on the mass market in 1998. Since then, several studies showing the positive effects of ESC has been presented. In this study, data from crashes occurring in Sweden during 1998 to 2004 were used to evaluate the effectiveness of ESC on real life crashes. To control for exposure, induced exposure methods were used, where ESC-sensitive to ESC-insensitive crashes and road conditions were matched in relation to cars equipped with and without ESC. Cars of similar or in some cases identical make and model were used to isolate the role of ESC. The study shows that the positive and consistent effects of ESC overall and in circumstances where the road has low friction. The overall effectiveness on all injury crash types except rear end crashes was 16.7 +/9.3 %, while for serious and fatal crashes; the effectiveness was 21.6 +/12.8 %. The corresponding estimates for crashes with injured car occupants were 23.0+/-9.2% and 26.9+/-13.9%. For serious and fatal loss-of control type crashes on wet roads the effectiveness was 56.2 +/23.5 % and for roads covered with ice or snow the effectiveness was 49.2+/-30.2%. It was estimated that for Sweden, with a total of 500 vehicle related deaths annually, that 80-100 fatalities could be saved annually if all cars had ESC. On the basis of the results, it is recommended that all new cars sold should have ESC as standard equipment. BACKGROUND The Electronic Stability Control, ESC or ESP, is an on-board car safety system, which enables the stability of a car to be maintained during critical manoeuvring and to correct potential under steering or over steering (1). In a general sense the equipment should eliminate loss of control. Since 1998, when the first mass-produced car with ESC standard equipment was launched, the market for cars with ESC has grown quickly. In Sweden, the proportion of new car sales equipped with ESC has grown from 15% in March 2003, to 69% in Dec 2004. ESC operates normally with both brakes and engine management. If the car loses control, defined as when one wheel or more is moving faster or more slowly than calculated from the steering input and turning angle, braking is applied to one or more of the wheels, and the engine power might be reduced. It has been expected, that the ESC will have a significant effect on loss of control type crashes. This effect is expected to have an influence both on the number and the severity of impacts (1), and might also change the orientation of the vehicle prior to impact (2, 3, 4). A projection of the effects based on in-depth data suggests that in 67% of the fatal and 42% of injury only crashes where the driver lost control, ESC would have a probable or definite influence (1). For all injury crashes, the estimated proportion of crashes addressed is 18%, for fatal crashes 34%. Several studies have been presented, demonstrating the effectiveness of ESC in real life crashes. A Swedish study (5) presented in May 2003 showed that there was a positive influence of ESC, especially in crashes on wet surface or surface covered by ice or snow. The effectiveness ranged between 20% and 40%, all being significant. Aga and Okado (6) showed that crashes dropped by 30 % to 35 %, and a German study (7) from 2002 showed a similar effect of ESC. Unselt et al (8) demonstrated a 30% reduction of crashes where the driver was at guilt and a 40% reduction of loss of control crashes. Two American studies have shown major effects of ESC. A NHTSA study (9), preliminary results show a 35% reduction of single vehicle crashes for passenger cars, and for fatal single vehicle crashes with 30%. Corresponding figures for SUVs were 67% and 63% respectively. Farmer (10) show similar results with a 34% reduction overall of fatal crashes. Other studies also express positive results (11, 12) While ABS (anti-locking brakes) also was subjected to high expectations prior to being available, several studies have shown that the effects are minor, or close to none (13, 14). While the crash type distribution has been found to be different for cars equipped with ABS compared to cars without, the net effect is probably less than 5% reduction of crashes with injuries (13, 14). With ESC, the situation seems to be different, with high expectations prior to real life experience but with high and consistent effectiveness in studies of real life crashes so far. The aim of the study was to: • Present a method and apply it to estimate the influence of ESC on crashes in Sweden • Estimate a possible reduction of real life crashes with injuries and for serious and fatal injuries separately.