Probability of Frontal Airbag Deployment in Vehicle Collisions
Accident reconstruction experts often determine the impact severity of a vehicular collision in their forensic investigations. A common collision severity index is Delta-v, or change in velocity of an object during a collision event. Airbag deployment thresholds can be a useful metric of collision severity in accident reconstruction applications. The National Automotive Sampling System (NASS) has provided a publicly-available database of real world motor vehicle collisions, including event data recorder (EDR) reports retrieved from airbag control modules. These reports typically indicate the airbag deployment status and the corresponding Delta-V of each recorded event.
This study is beneficial to accident reconstructionists, insurance staff, and legal counsel who may be investigating whether an airbag deployment was appropriate in a collision that may appear minor, or whether a non-airbag deployment was an anomaly or possibly due to a defective part based on statistical data.
Our analysis of the NASS EDR data revealed that the Delta-V threshold for a 50% probability of deployment event is higher for Toyota than for GM and Ford vehicles. In addition, SUVs and pickup trucks had higher deployment thresholds than sedans. An increase in Delta-V thresholds was observed for more recent vehicle model years. A higher Delta-V is required for frontal airbag deployment in underride collisions, in which a sedan contacted a vehicle with higher ground clearance (SUV, pickup truck, or van), compared to collisions with direct bumper-bumper engagement.
Effect of Manufacturer:
The statistical analysis indicates that in general, GM and Ford airbags deployed at lower Delta-V values than Toyota airbag systems. The Delta-V corresponding to a 50% occurrence of airbag deployment is 8 to 9 mph for GM, 9 to 10 mph for Ford, and 11 to 12 mph for Toyota. However, the Delta-V where 90% of collisions resulted in a deployment event converged at 18 to 19 mph across the three manufacturers.
Effect of Model Year:
Reports were categorized by model years 1994-2001 and 2002-2016, where the transition period 2001-2002 corresponds to pretensioners and dual stage airbags being introduced in vehicles . From our analysis, there has been a 1 to 3 mph increase in Delta-V thresholds for deployment between the years 1994-2001 and 2002-2016.
Effect of Vehicle Type:
The vehicle types studied are categorized by sedan, sport utility vehicle (SUV), and pickup truck. The findings indicate pickup trucks and SUVs generally have higher deployment thresholds than sedans. For example, the Delta-V corresponding to a 50% probability of airbag deployment is 7 to 8 mph for sedans, 9 to 10 mph for SUVs, and 11 to 12 mph for pickup trucks. This finding suggests size and weight of the vehicle may be factors in the deployment algorithm.
Effect of Impact Configuration:
Underride collisions occur in cases where the front of a vehicle collides with the rear of a vehicle with higher ground clearance. As a result, the bullet vehicle’s upper structure components (i.e. hood, grille, condenser, radiator support, engine block, etc.) contact the target vehicle’s bumper system. While cars in direct bumper-bumper impacts experience primarily compressive forces, the events in an underride collision involve both shearing to the sheet metal and compression to the bullet vehicle. Consequently, underride crashes were considered separately from collisions with bumper-bumper contact to evaluate the effect of contact height as a potential contributor in the airbag deployment criteria.
Underride data appear to trend towards a lower probability of airbag deployment for a given Delta-V range as compared to all frontal collision data. In other words, for a given likelihood of airbag deployment, the Delta-V threshold is higher in underrides than bumper-bumper collisions. A 50% probability of deployment corresponds to a Delta-V of 10 to 12 mph for underride collisions compared to 8 to 9 mph for bumper-bumper collisions.
An analysis of the NASS EDR database (over 9000 real-world collisions) indicates a 50% likelihood of airbag deployment corresponds to Delta-V of approximately 8 to 12 mph. Toyota vehicles had a higher Delta-V threshold than GM and Ford vehicles. The Delta-V thresholds increased by 1 to 3 mph between the years 1994-2001 and 2002-2016. SUVs and pickup trucks generally have higher deployment thresholds than sedans. A comparison of underride and bumper-bumper collisions suggests the Delta-V threshold for airbag deployment may be greater in underride collisions.
By Collision Reconstruction Consulting LLCABOUT THE AUTHOR: Felix Lee, MS PE
Accident Reconstruction Expert Witnesses California
Accident Reconstruction Expert Witnesses California
Felix Lee is the Principal Engineer at Collision Reconstruction Consulting LLC, a Los Angeles area firm specializing in motor vehicle accident reconstruction. Mr. Lee has investigated over 1,000 accidents and conducted engineering assessments of impact severity, vehicle speed and dynamics, collision sequence, occupant movement, damage matching, driver avoidance potential, event data recorders (EDRs), seat belt usage, airbag deployment, and rollover analysis.
Mr. Lee holds a Master of Science (MS) in Mechanical Engineering from the University of California, Los Angeles (UCLA). Mr. Lee also holds licenses as a Professional Engineer (PE) in California and as an Unmanned Aircraft Systems (i.e. drone) pilot through the Federal Aviation Administration. Mr. Lee is a certified Crash Data Retrieval (CDR) Technician and Analyst.
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Disclaimer: While every effort has been made to ensure the accuracy of this publication, it is not intended to provide legal advice as individual situations will differ and should be discussed with an expert and/or lawyer.For specific technical or legal advice on the information provided and related topics, please contact the author.