Obese Drivers Face Higher Risks in Cars

What Are the Reasons Behind Higher Death Rates?


  • Obesity Can Be a Factor in Car Death, Injury

    Obesity Can Be a Factor in Car Death, Injury

    Morbidly obese individuals are 56 percent more likely to die in a car crash than normal-weight individuals. | August 22, 2013

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The medical community continues to sound the alarm about obesity, with the American Medical Association recently declaring it a disease. Nearly 36 percent of Americans age 20 or older are considered obese, according to the federal Centers for Disease Control and Prevention. And while some health experts argue against the disease label, the reality is that being obese puts people at an increased risk for developing diabetes, heart disease and several types of cancer.

The health risks don't end there. Several recent studies found that obese people are not as safe behind the wheel. One culprit may be ill-fitting seatbelts, or the failure to use a seatbelt at all.

Increased Risk of Death
Obesity is defined as having a body mass index (BMI) over 30. A healthy BMI is between 18.5 and 25. Morbidly obese individuals, defined as those with a BMI of more than 40, are 56 percent more likely to die in a car crash than normal-weight individuals. That conclusion comes from a 2010 State University of New York at Buffalo analysis of national Fatality Analysis Reporting System (FARS) data of more than 155,000 drivers involved in severe motor vehicle accidents.

Those who were moderately obese, with a BMI between 35 and 40, were 21 percent more likely to die in a car crash.

A 2012 study by transportation safety researchers at the University of California at Berkeley and the University of West Virginia had more startling results: Drivers with a BMI between 30 and 34.9 had an increased risk of death of 21 percent. For those with a BMI between 35 and 39.9, the risk was 51 percent greater. Those with a BMI of 40 and over had an 80 percent increased risk of death.

Obese women fared even worse. Female drivers with a BMI of 35 to 39.9 had double the risk of dying in a car accident compared to normal weight female drivers. Morbidly obese female drivers were almost twice as likely as morbidly obese male drivers to be killed in a severe car crash, found the Berkeley and WVU researchers.

People who are obese often have other underlying health issues that contribute to them doing poorly if they have an accident, says Dr. Dietrich Jehle, a professor of emergency medicine at the University at Buffalo's School of Medicine and Biomechanical Sciences and author of several studies on how obesity impacts vehicular safety.

Interestingly, thinner isn't necessarily better when it comes to surviving a car crash. Both death-risk studies found that slightly underweight individuals were more likely than normal weight folks to die in a severe crash. The 2010 University at Buffalo study also found that normal weight folks had a slight risk of death, compared to overweight individuals with a BMI of 25-30. Slightly overweight drivers fared the best, with a 5 percent lower risk of death in a vehicular accident than those of normal weight.

Obese drivers may also develop health issues that make them less safe on the roads. Obesity is the leading cause of obstructive sleep apnea, (OSA) a chronic disorder that interrupts sleep and causes extreme daytime sleepiness and fatigue. Recent studies have found that people with sleep apnea are at twice the risk of being in a car crash, and three to five times more likely to be in a serious crash resulting in personal injury. OSA affects approximately 20 percent of U.S. adults, but 90 percent remain undiagnosed, according to the National Institutes of Health.

Form, Fit and Function
All vehicle manufacturers are conscious of their consumers, offering vehicles in a variety of shapes and sizes, but they are still using outdated safety models, says Matthew Reed, head of the biosciences group at the University of Michigan Transportation Research Institute, (UMTRI). "There aren't obese crash test dummies," says Reed.

When it comes to the design of crash test dummies, the car industry needs to catch up with America's growing waistline, agrees Jehle.

"One-third of Americans are overweight. Another third are obese, so it becomes a fairly significant issue when it comes to vehicle safety and design," Jehle says.

Vehicles today continue to be manufactured and safety tested using crash test dummies designed in 1976. According to the National Highway Traffic Safety Administration (NHTSA), the federal agency responsible for testing vehicle safety, the one most commonly used is the Hybrid III 50th Percentile crash test dummy. The female crash test dummy weighs 108 pounds. The male crash test dummy weighs 172.3 pounds. These represent adults of average weight, and are the dummies most often used in frontal impact tests to test a vehicle's restraining systems.

The Insurance Institute for Highway Safety (IIHS), an independent nonprofit organization that also tests vehicles with a starred safety rating system, doesn't have plans to make changes to the crash test dummies it uses.

"That may be something we look at in the future," says Russ Rader, a spokesperson for the IIHS. Regardless of crash dummy size, says Rader, vehicles on the road today are safer than ever before.

"The key thing we know from research that helps protect people in crashes is engineering vehicles that have strong structures, that protect the occupant compartment from collapsing," Rader says.

Vehicles rated as "Good" or better by the IIHS and those awarded four and five stars in NHTSA's test program protect people better than those rated less, Rader says. "They protect people no matter what their size, young or old, heavyset or thin."

The Problem With Buckling Up
Seatbelt usage saves lives in vehicular accidents, keeping occupants from being thrust forward or thrown out of a vehicle. "The single most important thing you can do to lessen your risk of injury in a crash is to fasten your seatbelt," says Rader.

But obese drivers often have difficulty with seatbelts, either wearing them the wrong way or not at all.

Here's one area where those slimmer crash test dummies make a difference. "Seatbelts are designed and tested on dummies to fit very snug, not loose," says Reed, director of UMTRI's Human Motion Simulation Laboratory.

A seatbelt works best when the belt rests close to the bone in your shoulder and in your pelvis, tight across the collarbone and low across the hip. In research using human modeling software, Reed has shown that obesity has a negative effect on seatbelt fit.

"In people who are carrying a lot of excess tissue, the belt is pushed forward and essentially it's slack," Reed explains. "So in a crash, especially a frontal crash, the vehicle stops and the person keeps sliding forward until the belt arrests."

"In an obese person, it has to push aside all of that soft tissue in order to get down to the bone where it can really start to slow a person down," he says.

A recent University at Buffalo study found obese drivers are less likely than normal weight drivers to use their seatbelts. Researchers analyzed FARS data of nearly 337,000 drivers involved in severe crashes where a death occurred. The more the person weighed, the less likely they were to wear their seatbelts, says Jehle, the study's lead author. Normal weight drivers were 67 percent more likely to wear seatbelts than drivers who were morbidly obese.

"The results weren't all that shocking," says Jehle. "For morbidly obese people, it's harder to put a seatbelt on properly, and harder to find ones that fit."

Morbidly obese people aren't just a marginal few individuals. More than 6 percent of American adults are morbidly obese, a rate that has risen rapidly in recent years, according to a 2012 study of data from the Behavioral Risk Factor Surveillance System.

Injury Risks
Research by Jonathan Rupp at UMTRI found that an increase in BMI increases the risk of serious-to-fatal injuries in vehicles crashes. Rupp used data from the National Automotive Sampling System-Crashworthiness Data System.

In frontal crashes, higher BMI increased the risk of both lower-extremity and upper-extremity injuries and of spinal injury. In nearside impacts, higher BMI increased the risk of upper-extremity injuries, but decreased the risk of lower-extremity injuries. BMI was not a significant predictor of serious injury for any region of the body in rollover or far-side impacts.

The front lower instrument panel, or knee bolster, is designed to absorb energy in a frontal crash. With obese individuals, the knee bolster is being asked to do a lot more work, says Reed, discussing his colleague's research.

"There's a compounding effect about it," says Reed. "The person is heavier, so it takes more force to stop them. And the belt is not fitting as well, which means the load sharing between the seatbelt and the knee bolster is not working the way it's supposed to. So what we see in the field is an increased risk in lower extremity injuries, in knees, ankles and feet, in people who are obese."

While these injuries aren't life-threatening, for obese individuals they can lead to an increase in morbidity and long-term disability, says Reed. "There are long-term health implications and a very high cost to the person who suffers them."

Unbelted obese passengers can also be a safety risk to the driver. Unbelted passengers seated behind a driver act as a "backseat bullet," slamming into them and potentially causing significant injury to the driver, which may otherwise have been avoided, found a 2004 analysis by the Center for Transportation Injury Research of NHTSA data of nearly 300,000 fatal crashes over seven years.

"The odds of death for the driver were 2.3 times greater if the person behind the driver isn't belted," says Jehle, the study's lead author. "If the person is heavier, the effect is going to be greater."

To stay safe behind the wheel, no matter your size, do the following:

  • Always wear a seatbelt and make sure your passengers do, too.
  • Make sure your seatbelt fits tight across your shoulder and low and tight across your lap. If you have significant girth around your waist, place the lap portion of the belt underneath the soft tissue, not over it, says Matthew Reed, head of UMTRI's biosciences group. The same goes for pregnant women.
  • If you need a seatbelt extender, first ask the vehicle manufacturer if they offer these. If they don't, ask which extenders are compatible with your vehicle's make and model.

"Seatbelt extenders are a good option for people who can't comfortably use regular seatbelts," says Russ Rader, spokesperson for the IIHS. However, NHTSA hasn't tested seatbelt extenders for safety and several car manufacturers do not offer them, citing the lack of testing on their efficacy in a crash.

When purchasing a new car:

  • Make sure you can buckle up with a seatbelt that fits properly. Many car manufacturers offer seatbelt extenders, or provide longer factory-installed belts, either as a free upgrade or for an added cost.
  • Look for a vehicle with enough "crush" space: the area between the seat and the steering column that helps absorb some of the force in a crash and provides a "cushion" of protection. "Obese drivers may be more susceptible to injury in an accident when there's less of a crush space," says Jehle, who is an expert in emergency medicine.
  • Choose a vehicle that allows you to sit in a safe driving position. According to the American Automobile Association, the ideal driving position is one in which there are 10-12 inches between the center of the steering wheel and the driver's breastbone. If a driver sits too close to the wheel, it can hinder steering and lead to fatigue. More importantly, it puts the driver at risk for airbag injury in the event of a collision.
  • Choose a bigger, heavier vehicle. "Bigger vehicles usually have longer front ends, with longer crush zones. The longer the crush zone, the longer the vehicle crushes and the lower the force on the occupants inside," said Adrian Lund, president of the IIHS, referring to a series of tests on the safety consequences of vehicle size and weight. "People in larger, heavier cars will fare better in crashes than people in smaller, lighter cars."
  • Buy a vehicle with a good safety rating from IIHS or NHTSA.
  • Consider a newer vehicle that offers electronic warning systems that make it easier if you are obese to back up and maneuver.
  • Check Edmunds' lists of cars, SUVs and crossovers, wagons and hatchbacks and trucks that are good for tall drivers. They have additional headroom, legroom and hiproom that may benefit overweight or obese motorists as well.

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