If the fact that winter is nearly over and warmer weather is on its way isn't enough to keep you motivated to stay on your diet and exercise program, consider that being overweight makes it more dangerous for you to be in a car. Specifically, a 2003 study by the RAC Foundation reports, overweight motorist have more than double the likelihood of being seriously injured or killed in a car accident than people who are not obese.

That result lead the RAC Foundation to ask carmakers to consider adding compensating safety features for overweight drivers - things like making sure seat height could be adjusted, installing tilting steering wheels, and extending the length of seatbelts.

They were backed up in their request by the results of two other studies:

A Seattle, WA study of 26,000 people who were involved in car crashes found that people who weigh between 220 and 260 pounds are roughly two-and-a-half times more likely to die than people weighing 130 pounds. That study also reports that body mass is the key factor rather than strictly weight - people whose BMI (body mass index) is between 35 and 39 are more than twice as likely to die in a car crash than those with a BMI of roughly 20. A BMI of 30 or more means you are obese.

A New Zealand study that looked at data from car accidents between 1988 and 1998 and then categorized them by body mass, dividing the involved parties into four groups found that obese people are twice as likely to die in car accidents, but it also found that thin people are more likely to suffer from broken bones, because they don't have enough body fat to cushion them from impact.

After looking at both studies, and conducting their own research, the RAC Foundation, an international research group, came up with a list of factors that may explain why obese drivers suffer from severe injuries and death so much more. Included among the listed items:

Crash-test dummies are generally based on average-sized men, rather than obese people of either gender.

Overweight drivers are more prone to such disorders as sleep apnea, and may be more likely to fall asleep behind the wheel.

A higher likelihood of high blood pressure, heart disease, and diabetes may factor into the numbers.

Car interiors are not always designed to accommodate larger drivers or passengers.

Seat belts and airbags are generally designed for average-sized passengers and drivers.

Of all of these factors, it is possible that seatbelts are the greatest issue. According to a report that was published in the journal

Obesity, only seventy percent of extremely obese people use their seatbelts all the time, as opposed to eighty-three percent of average-weight people. As well, more than half of those people who are killed in auto accidents are not wearing seatbelts.

While many auto manufacturers provide seatbelt extenders that can be installed at the dealership, others do not offer any accommodation for larger people. Still, auto makers are working to change things where they can. Smart air bags, for example, that can gauge the weight of a seat occupant, can be told not to trigger if a passenger or driver is too heavy, as well as too light, for them to be used safely.

Obesity is a medical issue caused by many factors, and it should never be assumed that a simple diet can control a morbid weight problem. However, if you are already taking steps to improve your physical condition, keep it up. Losing weight may protect you in a car crash.