Aditya Belwadi

Comparison of Crash Rates and Rear-End Striking Crashes among Novice Teens and Experienced Adults Using the SHRP2 Naturalistic Driving Study

ABSTRACT Objective: Motor vehicle crashes are the leading cause of death for teens. Previous teen and adult crash rates have been based upon fatal crashes, police-reported crashes, and estimated miles driven. Large-scale naturalistic driving studies offer the opportunity to compute crash rates using a reliable methodology to capture crashes and driving exposure. The Strategic Highway Research Program 2 (SHRP2) Naturalistic Driving Study contains extensive real-world data on teen and adult driving. This article presents findings on the crash rates of novice teen and experienced adult drivers in naturalistic crashes. Methods: A subset from the SHRP2 database consisting of 539 crash events for novice teens (16–19 years, n = 549) and experienced adults (35–54 years, n = 591) was used. Onboard instrumentation such as scene cameras, accelerometers, and Global Positioning System logged time series data at 10 Hz. Scene videos were reviewed for all events to identify rear-end striking crashes. Dynamic variables such as acceleration and velocity were analyzed for rear-end striking events. Number of crashes, crash rates, rear-end striking crash severity, and rear-end striking impact velocity were compared between novice teens and experienced adults. Results: Video review of the SHRP2 crashes identified significantly more crashes (P < 0.01) and rear-end striking crashes (P < 0.01) among the teen group than among the adult group. This yielded crash rates of 30.0 crashes per million miles driven for novice teens compared to 5.3 crashes per million miles driven for experienced adults. The crash rate ratio for teens vs. adults was 5.7. The rear-end striking crash rate was 13.5 and 1.8 per million miles driven for novice teens and experienced adults, respectively. The rear-end striking crash rate ratio for teens vs. adults was 7.5. The rear-end striking crash severity measured by the accelerometers was greater (P < 0.05) for the teen group (1.8 ± 0.9 g; median = 1.6 g) than for the adult group (1.1 ± 0.4 g; median = 1.0 g), suggesting that teen crashes tend to be more serious than adult crashes. Increased rear-end striking impact velocity (P < 0.01) was also observed for novice teens (18.8 ± 13.2 mph; median = 18.9 mph) compared to experienced adults (3.3 ± 1.2 mph; median = 2.8 mph). Conclusion: To our knowledge, this is the first study to compare crash rates between teens and adults using a large-scale naturalistic driving database. Unlike previous crash rates, the reported rates reliably control for crash type and driving exposure. These results conform to previous findings that novice teens exhibit increased crash rates compared to experienced adults.

Development of a Small Rear Facing Child Restraint System Virtual Surrogate to Evaluate CRS-to-Vehicle Interaction and Fitment

Child restraint systems (CRS) are the leading technology in providing safety and restraint to child occupants in automotive vehicles. Their success at reducing injury in motor vehicle crashes hinges largely upon their proper installation as well as their interface with the vehicle seat. To this degree, it is immensely important that vehicle manufacturers have an accurate means of producing seat design specifications capable of accommodating the large and varied CRS market in terms of safety, comfort and aesthetic appeal. However, to date there is no standardized method (the current recommended practice, SAE J1819, is archaic and inaccurate) of obtaining accurate geometries and volume representative of the current CRS market along with various combinations of rear-facing, forward-facing, and booster seats. Additionally, modern CRS designs have changed considerably to include greater side impact protection as well as design changes to enhance ease of installation. This study looks to correct the lack of accurate industry standardization and give a means of quantifying CRS geometry so vehicle manufacturers have access to true and current volumes thereby enhancing accuracy, fit and safety to the end consumer. In the current study, three-dimensional digital reconstruction of 22 CRS (rear-facing only CRS (RFCRS), convertible and combination) was accomplished by novel usage of the Microsoft Kinect for Windows sensor. In combination with 18 OEM drawings (made available due to the unique pre-competitive advantage of the Center for Child Injury Prevention Studies (CCHIPS)), a total of 40 child seats were compiled to represent 72 rear facing CRS in the current US market (as of April 2014). Digitized scans of CRSs were imported and combined into finite element (FE) models using ReconstructMe (PROFACTOR GmbH, Austria). The drawings were then edited for noise, extraneous data and assembled in the rear-facing configuration using Hypermesh 12.0 (Altair Inc., MI). Average vehicle seat-back (110°) and seat-pan angles (13.5°) were used (Reed et al. 2004) and the smallest configuration was developed in alignment with SAE J211 righthand co-ordinate system. The models were “shrink wrapped” to generate an overall volume and to protect critical CRS designs thus generating the smallest rear facing virtual surrogate model. A finite element (FE) model and surface data set (iges) of the “virtual surrogate” was made available to both vehicle and CRS manufacturers for virtual fitment evaluations in their respective design environment based on a pre-approved material transfer agreement. Based on both physical installations of the CRSs involved and virtual evaluation, the surrogate was found to accurately depict the volume and fitment of modern rear facing CRSs The use of virtual surrogates by vehicle manufacturers will be hugely beneficial over the outdated and rudimentary standards currently set in place. By alleviating manufacturers of the challenge of keeping seats and occupant space compatible with CRS, proper vehicle seat design can be applied early on to ensure optimal CRS-to-vehicle fitment. Proper fitment will promote ease of installation by the CRS consumer and improved protection and safety for the CRS occupant.

Comparative Performance of Forward-Facing Child Restraint Systems on the C/FMVSS 213 Bench and Vehicle Seats

Objective: The objective of this study was to evaluate the fidelity of the C/FMVSS 213 test bench, by comparing the dynamic performance of forward-facing child restraint systems (FFCRS) mounted on the C/FMVSS 213 sled bench versus mounted on a selection of production vehicle seats. Methods: The C/FMVSS 213 bench or one of 3 second-row original equipment manufacturer vehicle seats was mounted to the deck of acceleration crash sled. An FFCRS with a restrained anthropomorphic test device (ATD) was secured by 3-point belt (3-PT) or LATCH lower anchor (LLA) on the C/FMVSS 213 bench or vehicle seat, with or without a tether. The sled was then exposed to a 48 km/h acceleration pulse. Three unique make and model vehicle seats and FFCRS were tested. Fifty-three sled tests were performed. Results: When FFCRS were secured with LLA and no tether, little difference between the vehicle seats and 213 bench was observed. Similarly, when FFCRS were affixed with 3-PT and no tether, few kinematic variable differences achieved statistical significance; chest resultant acceleration was, on average, 9.1 g (SD = 6.6, P =.006) higher on the vehicle seats compared to the bench, as was CRS seatback excursion (difference [Δ] of 39.8 mm, SD = 32.7, P =.011) and ATD knee excursion (Δ = 36.4 mm, SD = 12.0, P < .001). However, when the tether was added to either the 3-PT or LLA attachment methods, the difference between the bench and vehicle seats was more pronounced. ATD kinematic measures such as head resultant acceleration (Δ = 14.6 g, SD = 7.2, P <.001) and pelvis resultant acceleration (Δ = 8.6 g, SD = 6.0, P =.005) were higher on the vehicle seats compared to the bench, as were the injury metrics for head and chest injury: ΔHIC15 = 162.2 (SD = 87.4, P =.001) and ΔChest 3 ms clip = 5.5 g (SD = 6.2, P =.040). Of note, CRS (Δ = 62.8 mm, SD = 32.7, P =.000) and ATD head (Δ = 66.3 mm, SD = 30.9, P =.000) and knee (Δ = 46.9 mm, SD = 25.8, P =.001) forward excursion were all higher on the vehicle seats compared to the bench in 3-PT with tether condition. Conclusions: Without the tether attached, we observed few kinematic and kinetic differences between the vehicle seat and the C/FMVSS 213 bench, suggesting that the bench is an adequate surrogate for the vehicle seat in this condition. With the tether attached, we found significant differences between the C/FMVSS 213 bench and vehicle seats, suggesting that the fidelity of the bench could be improved in the tethered mode. When differences were statistically significant, excursion and injury metrics were generally greater on the vehicle seats than on the C/FMVSS 213 bench.

Pediatric occupant-vehicle contact maps in rollover motor vehicle crashes

Objective: Rollover crashes account for more than 33% of all motor vehicle–related fatalities and have the highest fatality risk of all crash types, at 1.37% in the United States. There is increased awareness of the high fatality rate associated with this crash type, but there is very limited pediatric-specific data related to rollover crashes in the United States. Recent focus on rollover mitigation has resulted in implementation of countermeasures, making it important to evaluate injury causation for child occupants in rollover crashes with a more current data set. Methods: We queried the Crash Injury Research and Engineering Network (CIREN) from case years 1998 through 2013. Rollover crashes for passenger vehicles of model year 1998 or newer with at least one restrained occupant (excluding drivers) between 0 and 19 years of age were included. Vehicle-involved physical component and occupant–vehicle contact maps were developed with the CIREN data set. Results and Conclusions: Of the 20 CIREN cases that met the inclusion criteria, 15 had one or more injuries attributed to contact with some part of the vehicle structure. The CIREN analyses revealed that the head was the most common seriously injured body region, primarily due to contact with the roof side rail and/or vehicle interior. This finding was true for both adolescents and younger pediatric passengers in outboard seating positions. Fifty percent of head injury causation scenarios involving the vehicle interior had component intrusion of 20+ cm at the point of contact. Further exploration of pediatric rollover injury mechanisms using computational modeling and real-world testing is recommended in order to improve upon current mitigation strategies.