Occupant Safety in Vehicles Equipped with Automated Driving Systems, Part 2: Crash Safety Considerations for Out-of-Position Occupant Posture in Vehicles with Automated Driving Systems - Field Data Investigation

Panzer, Matthew B.; Shaw, Greg; Poplin, Jerry; McMurry, Tim; Kong, Kevin; Lin, Hongnan · 2021 · ROSA P / United States. Department of Transportation. National Highway Traffic Safety Administration

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Summary

This report investigates the crash safety risks associated with out-of-position (OOP) occupant postures in vehicles equipped with automated driving systems (ADS). The research is motivated by the expectation that ADS will allow occupants to engage in activities such as sleeping, reading, or conversing, leading to alternative postures like reclining or turning. These OOP postures may degrade the performance of standard restraint systems, which are designed for upright, midline seating. The study aims to quantify the frequency of OOP postures in the current vehicle fleet and assess their associated injury risks using field data. The researchers conducted a literature review and analyzed data from two primary sources: the Crash Injury Research and Engineering Network (CIREN) and the National Automotive Sampling System (NASS). The CIREN analysis involved two specific searches: one for occupants coded as "lying back" (limited to belted right-front passengers in frontal crashes) and another for those coded as "turned." The NASS analysis examined a broader sample to determine OOP frequency and injury patterns, including a matched-pair study to control for confounding variables like age and belt use. Findings indicate that OOP postures are currently rare, with only 0.5% of NASS subjects riding OOP. Among these, "sitting sideways or turned" was nearly as common as "lying back." The CIREN case study of seven "lying back" occupants revealed significant injury risks; four subjects sustained both cervical spine and abdominal injuries, attributed to poor belt fit and submarining. Investigators noted that altered shoulder and lap belt positioning contributed to these injuries. However, the broader NASS analysis failed to demonstrate a statistically significant increase in overall injury risk for OOP occupants. This lack of significance was largely due to the small sample size and the fact that OOP occupants were significantly younger than in-position occupants, an age factor that offset the increased risk associated with the posture and lower belt usage rates. Injury pattern analyses yielded inconsistent results across different study designs, though trends suggested higher rates of abdominal, neck, and lower extremity injuries for reclined occupants. The study concludes that while current data shows low OOP frequency, this will likely increase as ADS adoption grows. Because current restraints are optimized for upright postures, restraint performance is expected to degrade as OOP postures become more common, increasing injury risk. The authors emphasize that despite the anticipated reduction in crash frequency with ADS, occupant protection countermeasures must address OOP scenarios to ensure safety during the transition period. The findings support the need for further investigation into restraint systems that accommodate alternative postures, such as seat-integrated shoulder belts or active pre-crash seat adjustments.

Key finding

Field data analysis indicates that out-of-position occupant postures are rare in the current vehicle fleet, but reclined postures are associated with specific injury mechanisms like submarining and altered belt fit, while statistical evidence for increased overall injury risk is limited by low sample sizes.

Methodology

dataset

Provenance

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Summary generated by qwen3.6-27b-prismaquant on 2026-06-10; verification: verified.

Topics

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• demographic disparities

Information type

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• Empirical Findings: crash risk outcomes, observational prevalence