Whether you need to enter your car in both places depends upon the rest of your tax situation.
You will only need to enter your car under Deductions & Credits if you use your car for work as an employee (paid with a W-2). As an employee, commuting to work would not count. Only driving that you must do after you get to work - visiting clients, picking up supplies - would count for job-related travel expenses. As an employee, only those expenses that exceed 2% of your AGI will count.
As a contractor, you can't count your commuting expenses, either, only the driving that you must do after you get to work. But you can deduct all of your vehicle expenses directly from your income as a contractor. There is no threshold you have to exceed.
