Why Obese Drivers Are More Likely to Die in a Car Crash

Vehicle restraint systems are not 'one size fits all'

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Despite significant advances in automative restraint systems, many cars are less safe than they were more than thirty years ago.  Thanks to growing obesity rates - which affect our risk of illnesses like cancer and fatty liver disease - we simply don't fit in our car seats the way we used to, and that has a major effect on the way our bodies will react in a collision.

"Most of the restraint systems - including seatbelts and air bags - that exist now are based on old data from the 1970s and 1980s," observes Chris O'Connor, CEO of Humanetics, a global leader in the development of anthropomorphic test devices or ATDs.

 Commonly known as crash test dummies, these human replicas provide the basis for the design and testing of the safety and protection components of the vehicles we use.

"You have to think of the ATD as representative of the human body," O'Connor tells me.  "Every arm, leg, every body part. Weight, size, and centre of gravity are all anatomically correct. When we put sensors throughout the ATDs, we can monitor every rib, every section of the spine during impact; we can gather literally thousands of bits of information recorded in microseconds to know exactly what the resulting injury would be."

"Would they have broken a rib? Which rib? What damage would they have sustained?"

The problem, explains O'Connor, is that the crash test dummies in use today are based on decades-old anthropometry, or body measurements.

"In 1980 studies showed that a standard adult has a certain weight and dimension.

 In that year the obesity rate in the US was 15%, with an average BMI under 25.  Now 40% of our population is obese, with a BMI over 30.  The average driver or passenger today is not a slender person from 1980s data."

In vehicle restraint systems, size matters:  When adults gain weight, the extra girth isn't deposited evenly throughout our bodies.

 The weight gathers in our midsections, increasing our belly fat and shifting our position in the car seat.

"If you look at how a restraint system works," explains O'Connor, "it's based upon a narrow centre and thin waist.  Your seat buckle comes down, holds you where you're supposed to be held, with your back against the back of the car seat.  When you're heavier, you carry more weight in front and in back; your back end pushes you away from the seat back, leaving your centre of gravity further towards the front of the seat."

Obese people also tend to wear their seat belts differently, if at all; obese drivers and passengers will position the belt higher above their belly, instead of at its safest and most effective position against the pelvic bone.  A study published in 2014 in The American Journal of Emergency Medicine revealed that seatbelt use was 67% higher for car occupants of normal weight, when compared with morbidly obese drivers and passengers.

 Even slightly obese adults were less likely to wear a seat belt while driving.

Higher injury rate:  A 2013 study published in Emergency Medicine Journal examining almost 34,000 fatalities in motor vehicle accidents concluded that obese drivers are more likely to die from injuries sustained in a traffic collision than non-obese drivers or passengers involved in the same collision.

Bottom line for obese driver and passenger safety:  Humanetics CEO Chris O'Connor explains why his company has developed a new crash test dummy to more accurately reflect the drivers and passengers on the road today.

"We need to test cars against an obese version of the anthropomorphic device.  We're asking, 'how do we improve the odds for obese drivers?'"

O'Connor's company is also designing an ATD to reflect an aging driver population, since older vehicle occupants are also at higher risk of serious injury compared with younger people in the event of a vehicle collision.

More on traffic hazards:


Fryar CD, Gu Q, Ogden CL. "Anthropometric Reference Data for Children and Adults: United States, 2007–2010." National Center for Health Statistics. Vital Health Stat 11(252). 2012.

Jehle D, Doshi C, Karagianis J, Consiglio J, and Jehle G. "Obesity and Seatbelt Use: A Fatal Relationship. The American Journal of Emergency Medicine 2014 Jul;32(7):756-60.

Rice, Thomas M and Zhu, Motao. "Driver Obesity and the Risk of Fatal Injury During Traffic Collisions." Emerg Med J ISSN 1472-0205, 01/2014, Volume 31, Issue 1, pp. 9 - 12.

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