I can't say this enough: driving is a high-performance physical and mental exercise that requires your full concentration, and starts getting dangerous as soon as you're distracted or off your peak. Failing to recognise this is a primary cause of accidents.
And now this: Being obese can impair your performance sufficiently to make you a risk on the roads. In fact, the strongest predictor of crashing for younger drivers was body-mass index, along with regular consumption of alcohol (but not necessarily being pissed at the time). Not speed, but lard. Not the people who drink while driving, but the people who scarf hamburgers while driving.
Ironic, isn't it? The people most likely to jump in the car to go down to the corner shop for milk instead of walking are the people who are most dangerous while doing so.
Sum ergo cogito would like to remind people to pay attention to the road!!!