Overweight motorists are in danger, according to a leading British safety body. The RAC Foundation, an offshoot of the 6 million-member Royal Automobile Club, believes they are more than twice as likely to be killed or seriously injured in road accidents.
The foundation's medical adviser, Dr Tony Lavelle, cites several likely factors influencing the incidence and severity of accidents among large drivers ? including the fact that overweight people are more prone to sleep disorders and so more likely to fall asleep at the wheel.
Lavelle also says seat belts and airbags are generally designed for average-sized people and crash-test dummies reflect the vital statistics of the average person. Further, the design of car interiors may not be suited to heavier people.
The foundation says the higher death rate among overweight occupants may be due to factors such as high blood pressure, diabetes or higher likelihood of heart attacks.
"In a crash," its report says, "an unconscious obese person is more likely to choke as a result of swallowing their tongue before the arrival of emergency services [and] emergency services find it more difficult to remove larger occupants from crashed vehicles."
Drive found no major Australian studies linking weight with car accidents ? which, plainly, is a little-charted area. Attesting to this, the RAC Foundation's report relied on collated overseas research rather than new figures gathered in the UK.
The prime overseas research connecting body weight and car crash injuries came from Seattle. The study of 26,000 accident victims shows, according to the RAC, that people weighing 100kg-119kg are almost two-and-a-half times more likely to die in crashes than people weighing less than 60kg.
The Seattle study, the RAC says, "found that it was not just a question of weight but of obesity, as it looked at body mass index (BMI) ? that is, a measure that relates weight to height.
"People with a BMI of 35 to 39 (over 30 is obese) are over twice as likely to die in a crash compared with people with BMIs of about 20."
The second quoted study looked at data collected from New Zealand road accidents between 1988 and 1998 and divided casualties into four groups according to body mass.
Its conclusions are claimed to show the increased risk faced by overweight drivers ? but there was also bad news for the slender: "Thin people are less protected by body fat so had an increased risk of bone fractures."
Corroborating this last point, Bruce Priddle, Ford Australia's manager of environmental and safety engineering, says "in some ways lighter occupants are more frail". Priddle is not surprised by the RAC's claims but adds "we just don't have the data [in Australia] to prove heavy occupants are more vulnerable than light vehicle occupants".
Much of it comes down to physics, he says.
"If you double your speed, you multiply your kinetic energy by four. If you increase the mass by 50 percent then the energy increases by 50 per cent, so that amount of energy has to be dissipated somehow."
In a typical frontal barrier crash test at 56kmh, Priddle says the impact forces could be in "the 30 to 40 G area", meaning even the Everyman dummy effectively weighs up to three tonnes.
The RAC Foundation is calling on car makers to consider further in-car safety features to compensate for the extra hazards and to develop "large body" safety dummies.
Ford has just won the Society of Automotive Engineers' gold award for the safety systems in the BA Falcon. Priddle claims Ford tests for impacts on people verging on the heaviest 5 percent of the population and aims to give them the same protection as average-sized occupants. Two-stage airbags take into account the seat position to better protect passengers regardless of size.
Priddle stresses size is not the only factor in injury. "How you are built, bone size, the amount of padding you have, or how flexible or rigid you are, and a range of other factors can be very significant ... once you get over 40 your bones start to get brittle."
Monash University Accident Research Centre, has "dabbled in a couple of studies relating to weight and accidents", says Brian Fildes, professor of road safety. He says these did not involve a large sample, or conclusively prove a greater risk for large occupants. He was keen to follow up the RAC claims.
The foundation's executive director, Edmund King, says overweight drivers "have a responsibility to know the risks they are taking ... it would be fair to say that it comes down to the survival of the fittest as fitter occupants are more likely to survive a crash."