Per IRS Publication 502 Medical and Dental Expenses>, page 7:

Car. You can include in medical expenses the cost of special hand controls and other special equipment installed in a car for the use of a person with a disability.

Special design. You can include in medical expenses the difference between the cost of a regular car and a car specially designed to hold a wheelchair.

Cost of operation. The includible costs of using a car for medical reasons are explained under Transportation in IRS Publication 502.