Most of us don't think much about car insurance. We eyeball the policy every year, fiddle around with a few changes to bring down the premium, and then forget about it until the bills come. And come they do -- each exactly the same amount, no matter whether we've driven across the country or left the car in the garage. Counting the miles. Doesn't sound right, does it? Mileage -- like factors such as age and driving record -- has long been correlated with accident risk. The more you drive, the higher the chance of a crash. But unlike a …