I am unable to uncheck Department of Transportation Limits

If you are reporting your information on Schedule C, you can find the Department of Transportation limits in the General Info or Business Profile section of Schedule C.  

If you are using TurboTax Online, edit the General Info section and scroll to the bottom where you see Other Situations.  There you can Edit the answer to the Department of Transportation limits.

If you are using a CD/downloaded version of TurboTax, edit the Business Profile section of Schedule C and scroll to the Special Situations section at the bottom of the screen.  There you can Edit the section and uncheck the box for Department of Transportation limits.

If you are entering your information in the Employee Business Expense section, there is a check-box on a page asking about less common situations that indicates that you work in the transportation industry.  You can uncheck that box if it does not apply.