David Levinson:

you doubled up only a few times a week, you’re a strong candidate for downsizing, says David Levinson, a civil engineering professor and researcher at the University of Minnesota’s Center for Transportation Studies.
 
 Then, to compare costs, understand what you’re spending now. Charge all your gas purchases? Check your account statements to see last year’s damage. Add what you spent on maintenance and insurance. If you have a lease or loan, factor that in. Average new-car payments were about $482 a month last year, Experian says.