There is a 98% correlation between vehicle use and obesity rates. Therefore, it is extremely important to cut down on driving time.
Telecommute once a week or drive at low-traffic times.
Sitting in a car and driving is an extremely sedentary activity, and its negative effects are only exacerbated by having to drive through traffic. Try to take public transport to work or drive at low-traffic times to reduce the amount of time you spend seated.