Rear-End Impacts - Part 1: Field and Test Data Analysis of Crash Characteristics 2022-01-0859

Prior to developing or modifying the protocol of a performance evaluation test, it is important to identify field relevant conditions. The objective of this study was to assess the distribution of selected crash variables from rear crash field collisions involving modern vehicles. The number of exposed and serious-to-fatally injured non-ejected occupants was determined in 2008+ model year (MY) vehicles using the NASS-CDS and CISS databases. Selected crash variables were assessed for rear crashes, including severity (delta V), impact location, struck vehicle type, and striking objects. In addition, 15 EDRs were collected from 2017 to 2019 CISS cases involving 2008+ MY light vehicles with a rear delta V ranging from 32 to 48 km/h. Ten rear crash tests were also investigated to identify pulse characteristics in rear crashes. The tests included five vehicle-to-vehicle crash tests and five FMVSS 301R barrier tests matching the struck vehicle.

The analysis of NASS-CDS and CISS data indicates that more than 50% of exposed (MAIS 0+F) occupants were involved in a rear crash with a distributed impact and with no over-ride or under-ride. More than 93% were with a 6 o’clock PDOF. The average rear delta V was 21.3 ± 1.2 km/h (median 18.2, 90th CI 9.7-33.4) in the exposed (MAIS 0+F) occupant sample. For serious-to-fatally (MAIS 3+F) injured occupants, more than 88% were in a fully distributed rear impact and in 6 o’clock PDOF; 10.7% were in offset impacts and less than 1% were in narrow impacts. The average delta V was 35.9 ± 5.2 km/h (median 24.4, 90th CI 16.2-58.3) for serious-to-fatally (MAIS 3+F) injured occupants.

The results from the field data suggest that rear impacts with a delta V of 34-38 km/h and a 6 o’clock PDOF are representative of the average rear-crash scenario causing serious-to-fatal injury. Compared to the exposed occupants in the field data analysis, a 40 km/h rear sled is more than 1.9-times more severe than the average rear impact crash severity in terms of delta V and 4.4-times more severe in terms of crash energy. It is 1.11-times more severe than the average delta V for the serious-to-fatally (MAIS 3+F) injured occupant. It accounts for more than 90% of all occupants with injury (MAIS 1+F).

EDR data was helpful in accessing overall delta-V and impact duration information. For example, the average delta V in the EDRs included in the analysis was 38.7 ± 7.6 km/h and the average pulse duration was 129.6 ± 24.3 ms. Instrumentation data from crash tests provided more refined information for a detailed analysis of pulse characteristics.

The acceleration data obtained from the five vehicle-to-vehicle crash tests was investigated and compared to matched FMVSS 301 tests with the same struck vehicle. The data was scaled to a 40 km/h delta V pulse for comparison purposes. Bi-modal pulse shape characteristics were observed. The peak acceleration averaged 18.4 g in the vehicle-to-vehicle tests and 21.4 g in the FMVSS 301R tests. The average pulse duration was 147.2 ms and 123.8 respectively.

The results from this study suggest that using a 34-40 km/h bimodal-rear pulse with a 130-160 ms duration is representative of a serious real world rear impact.