The Japan New Car Assessment Program (JNCAP) was launched in 1995 in order to improve car safety performance. According to this program, installation conditions of safety devices and the results for braking performance and full-frontal crash test are published every year. The side impact test was introduced in 1999. In 2000, the offset frontal crash test was also introduced. From the viewpoint of such a diversification of the crash tests, an overall assessment method for the safety of cars which reflects road accidents has been demanded. In this study, we have examined a new overall assessment method capable of reflecting the traffic accident situation in Japan using methods employed or planned by USA-NCAP, Euro-NCAP, TUB-NCAP and others as references.
As the basic concept, JNCAP conducts three types of crash tests including the full-frontal crash test, offset frontal crash test, and side impact test to assess the dummy injury parameters. For the portions of the body which cannot be represented by the dummy injury parameters, the amount of car deformation is added to the assessment.
The dummy injury parameters are set by referencing the standards used in test methods and NCAPs conducted in overseas countries. In a conventional assessment method, dummy injury parameters are converted into a composite probability of the occurrence of injuries. In the new assessment method, dummy injury parameters are converted into scores using conversion functions. The conversion functions used to convert dummy injury parameters into scores were determined with reference to the risk curves relating to dummy injury parameters and the assessment functions employed by USA-NCAP and Euro-NCAP.
Scores converted from the dummy injury parameters are weighted according to portions of the human body and modes of collision. The weighting functions are determined taking into consideration the traffic accident situation in Japan and anticipated economic losses.
We have compared collision data for the same vehicle according to both the JNCAP method and the Euro-NCAP method in order to determine the differences in the rating methods. As a result, high overall correlation between these methods was confirmed.
The rate of scores for individual cars was calculated according to the Euro-NCAP method and the new assessment method. Cars scored high in the Euro- NCAP method also got high points in the new assessment method, although some minor differences were observed in the ranking.