Evaluation and Comparison of Roadside Crash Injury Metrics (2023)

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

213 14 Future Roadmap for Updates to MASH Injury Risk Evaluation Introduction and Objective Based on the findings from the current research effort, a proposed roadmap of research needs was developed to guide future potential updates to the MASH occupant injury risk evaluation procedures. While the focus of the current project was the improvement of existing MASH vehicle- based occupant injury criteria, there are other alternative injury risk evaluation methods that may become feasible in the future. The developed roadmap considered gaps identified through the synthesis of the published literature and gaps identified during the completion of the current research effort. The developed roadmap was divided into near-term and longer-term research needs. Summary of Future Occupant Risk Research Needs The research team identified research needs related to changes in the vehicle fleet, development of oblique impact ATDs, increased use of computer simulations, and the potential of AVs (Table 14-1). Table 14-1. Potential MASH occupant injury criteria research needs. Research Need Time Frame Implications of a Changing Vehicle Fleet on Roadside Hardware Occupant Risk Assessment Near-Term Use of ATDs to Assess Occupant Risk in Roadside Hardware Testing Near-Term Use of Computer Simulation to Assess Occupant Risk in Roadside Hardware Testing Near-Term Implications of Autonomous Vehicles on Roadside Hardware Occupant Risk Assessment Long-Term Occupant Risk Implications of a Changing Vehicle Fleet Much like the MASH test vehicles, the MASH occupant injury risk criteria should be regularly revisited to account for changes in the vehicle fleet. This project investigated the current FSM metrics and associated thresholds, as well as other potential crash severity metrics, as many changes to the vehicle fleet occurred since the inception of these procedures in the early 1980s. Our updates account for a number of significant advances to active and passive safety: frontal airbags, side airbags, side curtain airbags, dual stage airbags, improved vehicle crumple zones, increased belt usage, improved side impact performance, collapsible steering columns, increased prevalence of SUVs and CUVs, and increases in posted speed limits. While this work represents the occupant risk today, the vehicle fleet and environment will continue to evolve. There are advances in passive safety such as, but not limited to, belt pretensioners, active belt pretensioners, belt load limiters, knee bolster airbags, improved crash performance due to programs like NCAP and IIHS, increasing prevalence of SUVs and CUVs, and an increased prevalence of hybrid and electric vehicles.

214 14.3.1 Passive Safety Improvements There are a number of passive safety systems that will have significant market presence in the near future. Advanced restraints are one of the most promising passive safety features for front and rear-seated occupants. Advanced restraints are belts with an active pretensioner system and load limiter system. When a crash occurs, the active pretensioner system can rapidly remove any slack in the seat belt before the impact loads the occupant. Once the occupant engages with the restraints, the load limiter will allow the belt to spool out to minimize the total force loaded on the occupant’s thorax. This reduces the overall load on the occupant and leads to a significant reduction in the probability of serious injury. IIHS and NCAP assess vehicles in multiple crash tests and rate their level of occupant protection in a consumer-friendly format to use market forces to drive improvements to active and passive safety systems. IIHS recently updated their side impact test to continue to push the safety technology. These tests will continue to drive innovations to the vehicle crumple zones, the maintenance of the occupant compartment, and restraints. Another passive safety system gaining prevalence are knee bolster airbags. These are primarily intended to prevent the occupant from submarining under their lap belt by preventing the femur from sliding forward. These have shown the potential to reduce significant injuries. While these passive safety improvements can be slow to penetrate the vehicle fleet, all have the potential to reduce occupant injury risk. As occupant injury risk is reduced across the fleet, the selected MASH occupant injury risk thresholds would need to be revisited. 14.3.2 Vehicle Fleet Changes The vehicle fleet could continue to move toward SUVs and CUVs. In 2019, Ford announced that they will no longer sell sedans in the U.S., including the Ford Focus and Taurus. If other manufacturers take a similar approach, the prevalence of sedans in the U.S. fleet could rapidly decrease. SUVs and CUVs tend to have a higher CG, increased risk of rollover, and larger mass. In addition, electric vehicles will continue to increase in popularity. These vehicles have a number of key differences from traditional gasoline-powered vehicles. The electric vehicles have large battery packs typically stored in the floor of the vehicle. These battery packs cause electric vehicles to weigh significantly more than their gasoline engine counterparts and lower the CG. Therefore, electric vehicles tend to have lower rollover risk. Because electric vehicles lack an engine, the front of the vehicle often contains a second trunk. This could result in additional innovation to vehicle crumple zones since that space is no longer occupied by the engine. 14.3.3 Research Objective Because of the constantly changing vehicle fleet, the purpose of this future research would be to evaluate the MASH occupant injury risk procedures and associated threshold values. Specific objectives of this research effort could include: • Using the latest crash data from CISS to update the vehicle-based injury risk curves to reflect changes in the fleet.

215 • Revisiting the evaluation of other potential vehicle-based crash metrics such as ASI, VPI, and OLC based on the latest CISS crash data. • Assessing the available in-depth crash data for ability to identify specific passive safety improvements in vehicles to permit the evaluation of the effects of advanced restraint technologies, either on an individual or collective basis. • Proposing any needed changes to the current MASH injury thresholds. • Identifying emerging changes in the fleet that could affect the MASH injury criteria. 14.3.4 Implementation Considerations While the present study utilized NASS/CDS cases for the training dataset, future studies would use the latest CISS cases for the training dataset. This does present the question of the CISS 2020 data when those are released/available. Due to the COVID-19 pandemic, the cases sampled in 2020 and potentially 2021 may be very different than other case years. Despite the lockdown and reduced total vehicle miles traveled, NHTSA reported an increase in crash fatalities in 2020 (NHTSA 2021b). Due to the unknown repercussions of the COVID-19 pandemic on the quality of crash data, future updates using this methodology should consider including multiple case years before and after the pandemic and potentially consider excluding the 2020 case year. 14.3.5 Recommended Research Funding and Research Period Research Funding: $400,000 Research Period: 24 months Use of ATDs to Assess Occupant Risk in Roadside Hardware Testing Most FMVSS and NCAP crash tests continue to use the HIII 50th male and HIII 5th female ATDs. However, NHTSA is continuing to develop the HIII successor called THOR. Like the HIII, the THOR ATD has 50th male and 5th female varieties. However, unlike the HIII 5th female ATD, the THOR 5th female ATD is not a scaled down 50th male ATD. The THOR 5th female ATD incorporates anatomical and injury tolerance differences between males and females. Many FMVSS, NCAP, and IIHS crash tests now also include a 5th female ATD to assess the performance. One potential future research need is to investigate the feasibility of incorporating the THOR ATD family into the MASH occupant risk evaluation. 14.4.1 Validation of THOR in Oblique Impacts The purpose of the THOR family of ATDs is to provide a biofidelic response in both frontal and oblique crashes. Much of the current research on the oblique crash mode has focused on establishing response corridors based on PMHSs. Based on oblique PMHS tests, corridors have been constructed for chest deflection (Humm and Yoganandan 2020; Poplin et al. 2017) and head excursion, spine excursion, and pelvis excursion (Humm et al. 2018). Recently, the THOR chest deflection response was characterized in oblique and lateral far-side impacts (Yoganandan et al. 2019).

216 14.4.2 Development of Improved 5th Female ATD Multiple statistical studies have shown differences in injuries sustained by males and females (Bose et al. 2011; Kahane 2013; Parenteau et al. 2013). These differences have encouraged the development of the THOR 5th female ATD. The THOR 5th female ATD has a number of specific changes in design to account for sex differences (Wang et al. 2017). In general, the concepts for the THOR 5th female ATD are derived from the THOR 50th male ATD, but the anthropometry has been adjusted to the statistical 5th female rather than scaling the entire ATD down. Other female specific changes include integrating the breast with the sternum to reduce variability compared to the jacket on the HIII 5th female ATD. A statistical 5th percentile female pelvis was designed for the THOR 5th female ATD that is anatomically different from the male pelvis. 14.4.3 Research Objective Because of the potential improvements in the THOR ATD, the purpose of this future research would be to evaluate the inclusion of an ATD into the MASH injury criteria. Specific objectives could include: • Understanding how the ATD risk compares to the current MASH injury criteria, particularly in oblique crash modes. • Examining differences in the THOR 50th male ATD response and the THOR 5th female ATD response in oblique and frontal MASH tests. • Assessing the costs and benefits of including ATDs in the MASH crash test procedures and using the ATD response to evaluate occupant injury potential. • Evaluating the effect of ATD introduction to the injury criteria on current MASH hardware. 14.4.4 Implementation Considerations The response corridors for THOR ATDs in oblique crashes are still under development, and the injury risk curves for oblique impacts have not been established. Additionally, there have been changes to the physical design of the THOR ATD to improve its biofidelic response, and it could have additional improvements over the next few years. When the federal government implements the THOR ATD into the regulatory vehicle tests, this research need should be considered. Vehicle-based metrics have long been used instead of ATDs in roadside hardware crash testing for various reasons, including lack of an ATD validated in the oblique crash mode, as this crash mode is prevalent in roadside testing. While the THOR ATD may alleviate the lack of an ATD validated in an oblique crash, there are other relevant issues that would also need to be addressed prior to the implementation of ATDs in roadside hardware crash tests. These would include, but not be limited to, the following: 1. The ability to control the position of the ATD leading up to the impact. Roadside hardware crash tests use higher speeds and frequently use a vehicle-towing mechanism to achieve the desired impact speed. The roadside crash tests are frequently conducted in less controlled spaces (e.g., old airfields) rather than controlled indoor laboratory settings. As a result, an

217 ATD is more likely to be out of position in a roadside test prior to impact, which would influence the measured response of the ATD during the crash test. 2. The higher speed oblique impacts with longitudinal barriers prescribed by MASH have a reasonable chance for vehicle rollover. If rollover occurs, there is an increased likelihood that an ATD present inside the vehicle would be damaged. Depending on the frequency of occurrence, this could substantially increase the cost required to conduct such tests. 14.4.5 Recommended Research Funding and Research Period Research Funding: $1,000,000 Research Period: 36 months Use of Computer Simulation to Assess Occupant Risk in Roadside Hardware Testing There is currently no consensus among regulatory agencies such as NHTSA for using virtual crash testing (i.e., FEM) as a replacement for physical testing (Figure 14-1). Often, the current role of FEM is to predict the performance of a barrier or countermeasure before physical crash testing (Silvestri-Dobrovolny et al. 2016a), estimate the barrier performance in crash configurations not currently tested in MASH (Meng and Untaroiu 2020), or understand the performance in potential future crash scenarios (Jin et al. 2020; Schulz et al. 2020). In all of these use cases, the simulations require physical testing to validate the simulation results. However, it is possible for the FEM to be validated and accepted for very specific crash configurations. Because of the relatively low cost of FEM compared to physical crash tests, these simulations have the potential to reduce the testing timeline and allow for faster innovation in roadside hardware design. Figure 14-1. There is currently no consensus regarding the use of FEM for the regulatory testing of occupant risk. However, future MASH iterations may wish to re-consider this method, if and when it is accepted by federal agencies such as NHTSA. 14.5.1 Human Body Models There are multiple existing human body models and models of ATDs currently used in FEM analysis. There are FEM models of the entire HIII and THOR ATD family available from

218 Humanetics. For human models, there are Global Human Body Modeling Consortium (GHMBC) and the Total Human Model for Safety (THUMS). The GHMBC was developed by a consortium of OEM, federal, and academic stakeholders. The GHMBC includes model variations beyond the standard 50th male, 95th male, and 5th female sizes. There are GHMBC transforms to account for different heights and weights. In addition, the GHMBC can include the anatomical changes between sexes and that occur with age. Recently, the GHMBC model has been working to include muscle activation, which could be important to the biomechanical response at low-speed impacts. The THUMS model was developed by the Toyota Motor Corporation and was recently made publicly available at no cost to researchers. 14.5.2 Research Objective Due to the increased capabilities of FEM simulations, the purpose of this future research project is to evaluate the potential inclusion of FEM into the MASH occupant risk procedures. This could include: • Comparing different human body and ATD models such as the GHMBC and THUMS in various MASH crash test scenarios. • Understanding the difference in FEM occupant responses across size, sex, and age. • Estimating the cost of FEM implementation into MASH with respect to evaluating occupant injury risk. • Evaluating the effect of FEM testing on current MASH hardware. 14.5.3 Implementation Considerations The proposed research should consider carefully the validation required for using FEM as a tool to assess occupant risk. Previous research by Ray et al. (2008) developed generic procedures to validate FEM models against physical crash tests. While these could be used as a starting point, the procedures allow for model developers to generate and validate their own models, which results in many different models. Consideration should be given to a single unified FEM model available to all MASH test facilities and the associated issues with this approach (e.g., who maintains and updates the model). The research should also consider the benefits and costs of employing FEM to assess occupant risk in MASH tests compared to the benefits and costs of employing ATDs in MASH tests and the traditional vehicle-based injury assessment approach. 14.5.4 Recommended Research Funding and Research Period Research Funding: $500,000 Research Period: 24 months

219 Implications of AVs on Roadside Hardware Occupant Risk Assessment MASH, like most crash test procedures including NHTSA crash tests, assumes that occupants will be seated in forward-facing seats. Compared to current vehicles, AVs may have different occupant compartment configurations (Figure 14-2) that would expose occupants to very different loading environments. This could include rear-facing occupants, side-facing occupants, or even occupants not in an upright, seated position. Figure 14-2. Two concepts for innovative AV seating arrangements that may require updates to MASH occupant risk evaluation methods: rear-facing front seats with central table (left) and both inboard- and rear-facing seats (right). 14.6.1 HAVs and AVs The vehicle fleet is on a course toward fully autonomous driving. On the way toward the development of AVs, the vehicle is beginning to establish a role of assisting the driver in the operation of the vehicle, not just in emergency situations but also in normal driving. In emergency situations, active safety systems such as automatic emergency braking perform evasive actions to prevent or mitigate the crash. However, technologies such as adaptive cruise control and lane centering are intended to reduce driver fatigue by controlling the longitudinal and lateral inputs separately. While not currently on the road, highly automated vehicles (HAVs) will use a single system to operate the vehicle in normal driving scenarios under the constant supervision of the driver. While the driver is still in control of the vehicle, HAVs could lead to increased frequency of out-of-position occupants. Unlike HAVs, AVs are intended to operate without the input or oversight of a driver. This could allow occupants to be in alternate locations, positions, and orientations within the vehicle. 14.6.2 Research Objective Due to the increasing role of the vehicle in the driving task, the purpose of this future research is to understand the implications of HAVs and AVs on occupant risk assessment in roadside hardware testing. This could include: • Determining the most likely alternate seating locations and orientations within AVs.

220 • Reviewing the available published literature for physical tests and simulations to lend insight to occupant loads and/or forces for different occupant seating configurations. • Conducting physical and/or simulated roadside hardware crash tests with different occupant seating configurations. • Assessing the possible changes to the MASH injury risk evaluation procedures as a result of AVs and potential alternative occupant seating positions and/or orientations. 14.6.3 Implementation Considerations Historically, the design of roadside safety hardware was largely independent from vehicle design and safety (i.e., the design of the hardware must be such to accommodate a wide variety of vehicle types, sizes, and design features, with the hardware designers having to anticipate or react to changes in the vehicle fleet). The proposed research would benefit from a collaboration with one or more automakers to provide insight into the possible passive safety countermeasures for alternate occupant seating positions and/or orientations. 14.6.4 Recommended Research Funding and Research Period Research Funding: $800,000 Research Period: 30 months