Accident reconstruction experts often determine the impact severity of a vehicular collision in their forensic investigations. One common collision severity index is Delta-V (ΔV). The accident reconstructionists at Collision Reconstruction Consulting define Delta-V as the instantaneous 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, along with other analytical techniques. The National Automotive Sampling System (NASS) has provided a publicly-available database of real world motor vehicle collisions, including more than 10,000 event data recorder (EDR) reports retrieved from airbag control modules. These reports typically indicate the airbag deployment status and the corresponding Delta-V (ΔV) of each recorded event.
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 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 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 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.
Conclusions
Collision Reconstruction Consulting analyzed the NASS EDR database and determined the 50% likelihood of airbag deployment corresponds to Delta-V of around 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.
To download a complete text of this peer-reviewed SAE research study, please visit:
https://www.sae.org/publications/technical-papers/content/2019-01-0620/
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