I don't knit in the car any more because I do all the driving but yah I think you probably are. Here are some simple questions to determine knitting addiction.
Do you knit when ever possible?
Do you think about knitting more than 50 times a day?
When you see an attractive man or woman do you find yourself looking at their sweater instead of them trying to figure out the pattern and fiber?
Do you have 1 or more knitting dreams in a night?
Are you willing to give up cooking, cleaning, eating and sleeping if it means more time for knitting?
When you go on vacation do you book your hotel by it's location to the LYS?
Do you dream of rolling naked in your favorite yarn?
Do you order from KP at least twice a month?
Do you find yourself sneaking out to the LYS and then hiding your purchase?
If you've answered yes to 2 or more of these questions then you probably are addicted.
I'm sure there are other ways of telling addiction but these are the ones that have happened to me.