The Mileage Tax Deduction. The Mileage Tax Deduction is a credit made for the 21st century. The amount of road travel we engage in for the most common aspects of our life is either wonderful or absurd depending on how you view things.ou get the choice of claiming the actual vehicle expenses deduction or taking the mileage rate. Obviously you want the one that affords you the biggest advantage. The actual expense deduction includes: 1  Gas.