The New Car Assessment Program Has It Led to Stiffer Light Trucks and Vans over the Years? 1999-01-0064

Since model year 1983, one hundred and seventy five light trucks, vans, and sport utility vehicles (LTVs) have been included in the New Car Assessment Program (NCAP) frontal crash tests. In this frontal test, vehicles are crashed at 35 mph such that the entire front impacts against a rigid, fixed barrier. Instrumented anthropometric dummies are placed in the driver and right front passenger seats. Accelerometers are placed on the vehicle to record the response of the structure during the crash.

A number of recent papers have examined the compatibility of LTVs and cars in vehicle-to-vehicle collisions. The studies in these papers, generally, consider three factors for vehicle-to-vehicle compatibility: (1) mass, (2) stiffness, and (3) geometry. On June 5, 1998, Transport Canada and the National Highway Traffic Safety Administration held a forum entitled “Transport-NHTSA International Dialogue on Vehicle Compatibility,” in Windsor, Canada. At the forum, representatives of major vehicle manufacturers expressed the view that NCAP has led to the design of more aggressive stiffness parameters for LTV front structures. With crash data on 175 LTVs distributed over the last 15 model years, it is possible to examine and analyze the actual trends of the stiffness and structural characteristics of this class of vehicles. In this paper, the acceleration data from accelerometers in the occupant compartment and from the dummies are analyzed to determine:

1. 1
   the trend of total stiffness or aggressivity characteristics of LTVs since MY 1983,
2. 2
   the trend of the approximate linear stiffness of LTVs during the first 200 mm of crush since MY 1983, and
3. 3
   the effect of these structural characteristics on the NCAP safety ratings.

Three parameters, that are associated with energy management and with the crushing of the front structure (the crash signature of crash pulse) of the vehicle, are studied relative to the total stiffness or aggressivity of LTVs. These three parameters are (1) maximum dynamic crush, (2) maximum acceleration of the vehicle structure, and (3) the time period of the acceleration pulse. Approximate linear stiffness values are calculated from the occupant compartment accelerations and the vehicle masses for the first 200 mm of vehicle crush during the rigid barrier impact. The stiffness of these first 200 mm is an approximate measure of the structural aggressivity of the striking vehicle in front to side impacts. The effect of these aggressivity and stiffness parameters on the dummy responses is examined. It is shown that, on the average,

1. 1
   the maximum dynamic crush and the time period of the acceleration pulse have increased over time. The maximum acceleration of the vehicle structure has decreased over time.
2. 2
   the approximate linear stiffness in the first 200 mm of crush has decreased over time, and
3. 3
   there is a correlation between lower stiffness and aggressivity parameters and better NCAP scores.

These findings indicate that NCAP may have influenced manufacturers to design less aggressive, and, therefore, more compatible LTV front structures for both front to front and front to side impacts.