Researchers analyzed the National Automotive Sampling System/Crashworthiness Data System (NASS/CDS) 1998-2002 to examine the characteristics of single and multiple impact crashes. In addition to a statistical analysis, individual cases were studied to determine factors that contributed to injury risk.
Multiple impact crashes (MICs) make up 42 percent of all tow-away crashes that occurred on US roadways between 1998 and 2002. The risk for highseverity injuries is about 1.5 times greater in MICs than single impact crashes in moderate and highrange delta velocities. The average delta velocity values of single impact crashes (SICs) and MICs are similar in all tow-away crashes. Impact speeds for MICs resulting in MAIS3+ (Maximum Abbreviated Injury Scale: level 3 or greater) injuries are lower than that for SICs. A frontal crash followed by a second frontal crash occurs most often, followed by near-side/near-side and front/near-side multiple impact crashes.
After the initial investigation of MICs, belted drivers became the focus of this study, because the kinematics of unrestrained occupants is often too complicated. The most harmful category is front followed by front MICs for the population of belted drivers analyzed.
Based on case reviews, the researchers found that multiple impact crashes could be better described by separating them into two categories – incidental and consequential. For the incidental cases, only one impact was influential in the injury outcome. In consequential cases, both impacts were 15 mph (24 km/h) or greater delta velocity. Cases with higher severity secondary impacts were also classified as consequential.
The following were associated with increased injury severity in consequential MICs: more than one injurious impact; initial injury exacerbated by the second impact; the first impact caused the occupant to be out of position for subsequent impacts; crumple zones exhausted by the first impact; safety devices deployed during the first impact making them unavailable for subsequent impacts.
The frequency and injury risks for each combination of MICs are shown in this paper.