Abstract
Head-to-vehicle contact boundary condition and criteria and corresponding thresholds of head injuries are crucial in evaluation of vehicle safety performance for pedestrian protection, which need a constantly updated understanding of pedestrian head kinematic response and injury risk in real-world collisions. Thus, the purpose of the current study is to investigate the characteristics of pedestrian head-to-vehicle contact boundary condition and pedestrian AIS3+ (Abbreviated Injury Scale) head injury risk as functions of kinematic-based criteria, including HIC (Head Injury Criterion), HIP (Head Impact Power), GAMBIT (Generalized Acceleration Model for Brain Injury Threshold), RIC (Rotational Injury Criterion), and BrIC (Brain Injury Criteria), in real-world collisions. To achieve this, 57 vehicle-to-pedestrian collision cases were employed, and a multi-body modeling approach was applied to reconstruct pedestrian kinematics in these real-world collisions. The results show that head-to-windscreen contacts are dominant in pedestrian collisions of the analysis sample and that head WAD (Wrap Around Distance) floats from 1.5 to 2.3 m, with a mean value of 1.84 m; 80% of cases have a head linear contact velocity below 45 km/h or an angular contact velocity less than 40 rad/s; pedestrian head linear contact velocity is on average 83 ± 23% of the vehicle impact velocity, while the head angular contact velocity (in rad/s) is on average 75 ± 25% of the vehicle impact velocity in km/h; 77% of cases have a head contact time in the range 50–140 ms, and negative and positive linear correlations are observed for the relationships between pedestrian head contact time and WAD/height ratio and vehicle impact velocity, respectively; 70% of cases have a head contact angle floating from 40° to 70°, with an average value of 53°; the pedestrian head contact angles on windscreens (average = 48°) are significantly lower than those on bonnets (average = 60°); the predicted thresholds of HIC, HIP, GAMBIT, RIC, BrIC2011, and BrIC2013 for a 50% probability of AIS3+ head injury risk are 1,300, 60 kW, 0.74, 1,470 × 104, 0.56, and 0.57, respectively. The findings of the current work could provide realistic reference for evaluation of vehicle safety performance focusing on pedestrian protection.
Highlights
In vehicle-to-pedestrian crashes, injuries to the head account for more than 30% of all AIS2+ (Abbreviated Injury Scale) injuries to pedestrians (Mizuno, 2005), which are the main causes of pedestrian death (Yang, 2005; Simms and Wood, 2009; Schmitt et al, 2010)
In the current C-IASI and C-New Car Assessment Programs (NCAPs), the adult head impactor test area for pedestrian protection mainly focuses on the WAD range 1.7–2.1 m (C-IASI, 2017; C-NCAP, 2020), so about 30% of adult head contacts on the vehicle observed in the current study are not included (Figure 7)
The results show that the WAD is influenced by pedestrian height and vehicle impact velocity, where a positive linear correlation is observed for the relationship between pedestrian WAD/height ratio and vehicle impact velocity (Figure 11D)
Summary
In vehicle-to-pedestrian crashes, injuries to the head account for more than 30% of all AIS2+ (Abbreviated Injury Scale) injuries to pedestrians (Mizuno, 2005), which are the main causes of pedestrian death (Yang, 2005; Simms and Wood, 2009; Schmitt et al, 2010). In NCAPs, subsystem tests using isolated impactors with the consideration of head-to-bonnet/windshield area impacts are employed, where the definition of the impact boundary condition and the criterion and corresponding thresholds for head injuries are crucial since these have a significant influence on vehicle safety (pedestrian injury risk) rating (C-NCAP, 2020; Euro-NCAP, 2020). The thresholds or risk curves of human head injuries at different AIS levels were proposed for these criteria, based on data from physical impact tests, reconstruction of real-world accidents (football players, motorcyclists, pedestrians, etc.) using isolated Anthropomorphic Test Devices (ATDs) and/or numerical human body models of head (Kimpara and Iwamoto, 2012; Marjoux et al, 2008; Newman, 1986; Takhounts et al, 2011 and 2013). Few studies have focused on developing injury risk curves from reconstruction of real-world pedestrian crashes at the full-body level, covering all the above-mentioned kinematic-based criteria, where the influence of restriction from the torso and lower body on pedestrian head dynamic response and the cumulative head kinematics in the whole impact can be considered
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