Krafft 1 THE CORRELATION BETWEEN CRASH PULSE CHARACTERISTICS AND DURATION OF SYMPTOMS TO THE NECK – CRASH RECORDING IN REAL LIFE REAR IMPACTS

AIS 1 neck injuries has become the most common disabling injury in vehicle crashes. Research has shown that there are variations in rear impacts causing shortand long-term disability to the neck. Therefore impacts in where the duration of symptoms differ need to be separated in analyses. Crash severity is usually measured as change of velocity. The correlation between injury risk and impact severity parameters based on acceleration levels is to a high extent unknown. Since 1995, approx. 15,000 vehicles on the Swedish market have been equipped with crash pulse recorders measuring the acceleration time history in rear impacts. In the present study, the results from crash recording of 34 real life rear impacts were analysed where the change of velocity and the crash pulse were measured. The injury status of the 49 front occupants was classified as no symptoms, or symptoms less or more than 1 month after the impact. Also injury risk functions were calculated for different duration of symptoms correlated to the crash severity parameters. Most of the occupants that sustained symptoms more than 1 month, the change of velocity was higher than 15 km/h and the mean acceleration more than 5g. The average impact speed and mean acceleration for this group were 23km/h and 5.4g. Furthermore, the crash pulses form a corridor with acceleration between 5 and 10g and duration between 80 and 150ms. Those occupants that sustained symptoms less than 1 month, the average change of velocity were 10 km/h and the mean acceleration was 3.5g. When designing test methods for evaluating vehicle safety concerning AIS 1 neck injuries, the acceleration pulse will differ considerably depending on focusing shortor long term consequences. INTRODUCTION Few studies have distinguished between the duration of the symptoms and the influence of the crash severity. For 12 months Olsson et al (1990) followed the progress of 33 occupants involved in rear impacts in Volvo cars. No clear relationship was found between impact speed (measured as EBS) and the initial spectrum of symptoms or the duration of symptoms. However, EBS (Equivalent Barrier Speed) or change of velocity calculated with retrospective methods has too low accuracy to predict the crash severity (Kullgren 1998), especially in low speed impacts (Lenard et al. 1998). A slight correlation was claimed between the duration of neck symptoms caused by rear impacts and the degree to which the impacted vehicle was deformed when on the rear side members had been activated. Krafft et al (1999) found a relationship between the crash pulse on the neck injury risk in rear impacts, by studying the same car model with and without tow-bar. It was found that a tow-bar on the struck car increased the risk of long-term consequences with approximately 20% than without. The definition of long-term consequences was symptoms at least one year after the impact. An earlier study, Krafft (1998) showed that a longitudinally mounted engine (compared with a transversal one) in the striking car also increased the risk of long-term consequences in the struck car. Following studies describe the impact severity when no injury or short-term consequences occur. Mc Connell et al (1995) performed low-speed rear impacts with seven male volunteers, with velocity changes of up to 10.9 km/h. None of the volunteers reported whiplash symptoms after a few days. Ono and Kaneoka (1997) and Siegmund et al (1997) found similar results from volunteer tests. In another study with volunteers (Eichberger et al 1996), where the sled impact velocities were 8-11 km/h and the mean deceleration 2.5g, the volunteers suffered whiplash symptoms for approximately 24 hours.