Per IRS Publication 502 Medical and Dental Expenses (Including the Health Coverage Tax Credit), on 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, later.

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