Assessment of Injury Criteria in Roadside Barrier Tests

Chi, M. · 1976 · ROSA P / United States. Federal Highway Administration

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Summary

This 1976 report by Michael Chi, commissioned by the Federal Highway Administration, addresses the lack of rational, theoretically grounded injury criteria for evaluating roadside barrier performance. The study was motivated by the need to mitigate human injuries in vehicle-barrier crashes and to replace existing standards, which were largely empirical, inconsistent, and often derived from aerospace contexts that did not accurately reflect highway crash dynamics. The primary goal was to establish reliable thresholds for fatal or irreversibly disabling injuries to guide the engineering of guardrails and median barriers. The methodology involved a critical review of existing literature, including the widely cited but flawed Shoemaker criteria, Graham’s 10G theory, and military specifications. The author analyzed the evolution of these standards, identifying inconsistencies in parameters such as duration, onset rate, and restraint conditions. Using simple mathematical models and biodynamic principles, the report evaluated injury mechanisms across different time durations, distinguishing between impact, hydraulic, and dynamic force phenomena. The study specifically challenged the prevailing emphasis on "onset rate" (jerk) and peak deceleration, arguing instead for a focus on momentum change and average deceleration. The findings demonstrate that existing criteria were overly empirical and often misleading. The report concludes that for short-duration impacts, injury is determined by velocity change (momentum change) rather than peak deceleration, while longer-duration loads are governed by average acceleration. The author refutes the significance of onset rate limits, showing that overshoot effects depend on the ratio of rise time to the body’s natural period, not the onset rate itself. Consequently, the report recommends a new set of injury criteria based on average deceleration and velocity change up to the instant of secondary impact. It proposes using Kornhauser’s sensitivity curves, modified by Payne, which define tolerance limits as either a maximum velocity change or a maximum average acceleration, depending on the duration of the event. The significance of this work lies in its shift from empirical observation to a rational, physics-based approach for injury assessment. By clarifying the roles of duration, velocity change, and acceleration, the report provides a more accurate framework for designing roadside barriers that protect occupants. It highlights the limitations of transferring aerospace injury standards to highway safety and emphasizes the importance of accounting for restraint systems and occupant kinematics. The recommended criteria offer a clearer, more conservative basis for preventing fatal and disabling injuries, influencing future standards for vehicle crash testing and barrier design.

Key finding

Injury thresholds for roadside barrier impacts should be defined by average deceleration and velocity change rather than peak acceleration or onset rate, with specific tolerance limits established for fatal and irreversible injuries.

Methodology

review

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Information type

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• Empirical Findings: crash risk outcomes