DETROIT — Like most Americans, the drivers of Detroit are required to carry auto insurance whenever they get behind the wheel, but many law-abiding residents can’t afford the Motor City’s highest-in-the-nation auto premiums, which top $5,000 a year in some neighborhoods.So fully half of Detroit drivers do what’s known locally as “driving dirty” — taking to the streets without any coverage. It’s practically a tradition here.Now Mayor Mike Duggan is trying to do something about …