The Roll Over Incident: Who's Driving? Case Study Transcript

Shaun Jeffs, MS, PE:

The story that was brought before us was that there was this rollover collision and one of the occupants, the male, was ejected during the collision. He was ejected and he received fatal injuries. We were tasked with analyzing the physical evidence, doing inspections to see if we could determine which of these two occupants was driving at the time. In a case like this where there's a rollover, it's a high energy event, damage tells a story. For me as a biomechanical engineer, I'm looking at evidence and damage on the interior of the vehicle, and so we were taking a look at that truck to see if there was any indication of occupant motion within the vehicle.

There were three key pieces of evidence that we found during that inspection. The first was seatbelt evidence. We're trying to determine if people were wearing seat belts, and if they did, is there a way to tell who was in which seatbelt? When we all wear our seat belts, we grab what's called the latch plate. That's a little metal piece that has a tongue, and we pull that over our shoulder and we buckle it into the buckle. Well, if you look carefully, that latch plate, the belt routes through a little slot in that latch plate.

That slot is generally made of plastic, and so when a vehicle rolls, it's spinning and spinning and spinning, and the occupants are forced outwards. That force causes the body to load the seatbelt, seatbelt locks, and your body's trying to get out of the vehicle. The force of that seatbelt holding you in place causes that belt to drag through that slot in the latch plate. It actually melts the plastic because there's a lot of force, there's a lot of velocity, and so a lot of times you'll get little hairs of plastic embedded in the seatbelt webbing. We know that the daughter was in the rear bench of the vehicle.

The right rear passenger seatbelt had very obvious evidence of occupant loading. In addition, I took a really close look at that latch plate and there were scratches, parallel scratches across that load-bearing surface, and that told me that for sure that seatbelt was being used at the time of the collision. I looked at the front seat belts as well, and neither of those had the same level of evidence. We came to the conclusion that neither of those front seat belts were being used at the time of the crash.

The second thing I was looking at was ejection portal, so we know that the male was ejected, but we looked at all the windows which were broken out. There was one particular window that had evidence of an occupant moving from inside to outside. There were scratches and gouges on the trim around the door. It's been shown through peer-reviewed studies that occupants sitting in a vehicle when involved in a rollover, if they're going to be ejected, they go out the ejection portals that is closest to them or adjacent to them. If you've ever gone to a carnival and ridden one of those Gravitron rides, it's a big wheel, you stand up against the wall on the outside edge of the wheel, and then that wheel starts spinning and spinning and spinning. If you ever ridden it, you felt that there is a force that's pushing you back into the wall, and that's a good example or a good demonstration of centrifugal acceleration. And so it would stand to reason that since he was ejected out that right front window, the closest seat to that would be the right front passenger seat.

As we're looking at a complicated case like this, you're looking for any and all pieces of evidence. As I was inspecting the truck and looking at that right front window, I actually found a sunglass lens that was embedded in the window frame. As I continue to look through all the debris and things that were inside the vehicle, we actually found a photograph of the man and the woman together. In that photo, he was wearing a pair of sunglasses. We continue to look further and we actually found that pair of sunglasses, and so we knew that those sunglasses belonged to him. We knew that the sunglass lens fit those frames that were with the debris inside the car. If he was wearing those sunglasses at the time of the crash, they would've been deposited in that location.

One of the really helpful tools we have available as biomechanical engineers is to conduct what's called an exemplar and surrogate study. We get a vehicle that's the same year make model as the vehicle involved in the crash. We get human surrogates as stand-ins for the people that were involved in the crash. What that helps us do is, for one, be able to visualize what that person looks like in that vehicle. When we inspected the subject truck, the seats were adjusted in a certain way, so what we were able to do with the exemplar vehicle is replicate and duplicate that seating position. When we put the male surrogate inside that seat, his knees were touching the dashboard. This would not have been a comfortable position to drive in. Then we had the female surrogate sit in that same seat. The seating position was much more consistent for a person of the size of the female occupant.

At the end of the day, what we were asked to do is determine who was driving during this accident. Through the analysis of the physical evidence and known kinematics of occupants in rollover collisions, we determined that the woman was the driver of the truck.

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