A test method for evaluating safety aspects of ESC equipped passenger cars : a prototype proposal

Abstract

This paper will discuss how active safety systems are becoming increasingly common in today’s vehicles. Electronic Stability Control (ESC) systems were introduced during the end of the 1990s, and accident statistics show that they have had a huge impact on traffic safety. In the USA, a new legislation has recently been adopted which demands on every new light vehicle that is sold to be equipped with ESC, beginning 2011. New systems require new testing methods, and there is a need expressed by the New Car Assessment Program (NCAP), which at present time only evaluates the passive safety of cars, also to include tests for active safety systems. In a previous VTI work, a literature review regarding methods for the evaluation of traffic safety effects of Antilock Braking Systems (ABS) and ESC was performed. Based on the findings of that review, we have proceeded with defining a test method for evaluating safety aspects of ESC equipped passenger cars. The objective has been to suggest a (prototype) test method that can be used for a more holistic evaluation of the safety effect of ESC in cars, including the driver behavior perspective. From discussions with leading experts on traffic safety and ESC, possible benefits of ESC systems on traffic safety were identified. In addition to increasing the yaw stability of the vehicle, the following ESC benefit effects were identified: (1) A warning system for slippery roads. ESC activation indication may act as a warning system to the driver about slippery road conditions. (2) Reduced collision speed. In a critical situation, ESC activation may reduce the collision speed, which will mitigate the outcome of the collision. (3) Improved vehicle roll stability. The ESC system may also stabilize the vehicle with respect to untripped rollovers. Most rollovers are however tripped rollovers, which can occur when a vehicle, with some lateral slip, strikes an object or slides off the road. These rollovers also benefit from the ESC system as it aids in keeping the vehicle on the road. Test methods for the single benefits were proposed, but further research is needed before it will be possible to assess the relative importance of each benefit. Research on the driver behavior aspect of ESC was initiated by focus group study. These early results suggest that drivers do not rely on the support systems of the car, but drive according to road and traffic conditions, as well as their own perceived skill. As a test of yaw stability performance, a maneuver conducted with a steering robot, such as the National Highway Traffic Safety Administration’s (NHTSA) Sine with Dwelltest, was considered to be better than a test involving human test drivers. This maneuver has been specified in detail by NHTSA, but further research is needed regarding the choice of test surface and the influence of tires. Future studies based on the findings in the report were proposed. There is a clear need to study the aspects of driving behavior with ESC in a more quantitative way using a driving simulator. Such a study would be designed also to increase the knowledge regarding the benefit effects. Two field tests, one performed on dry asphalt and one on ice/snow-surface, incorporating a small number of vehicles and a range of different tires are also needed for finalizing the yaw stability performance test.