Last month a study found that on average seat widths and the thickness of their padding in cars hadn’t changed much over the past ten years despite increases in the size of the average driver’s waistline over the same period. This is also the case with seatbelts. In fact, federal standards for the length of a seatbelt in countries like the U.S. date back four decades and only require that belts are able to accommodate at most a 215-pound man.

Some carmakers do offer bigger belts or extenders but many don't because of concerns about effectiveness and liability, reports the Associated Press. A new study conducted by Vanderbilt University psychologist David Schlundt has found that the more overweight a person is, the less likely they are to wear the life-saving device. "They really have a hard time getting that belt buckle over them," Schlundt said. "They have to stretch it out and then over and then some can't see the buckle."

The study found seatbelt use declined as body mass index (a common measure comparing a person’s weight to their height) increased. Some of the stats were alarming. Only 70% of extremely obese people always wore a seatbelt and only 83% of normal sized people always wore a seatbelt, according to the responses of more than 250,000 drivers in the U.S. The best solution researchers found is to install seatbelt extenders, which can add around 18-20in to the length of the belt, but they can be hazardous, too, if used by passengers who are too small.