it is not considered taxable income?
I'm assuming you're not an employee. The IRS "accountable plan" rules wouldn't apply to you. As noted in Publication 463, in an accountable plan "Your expenses must have a business connection — that is, you must have paid or incurred deductible expenses while performing
services as an employee of your employer." Nonetheless, I can't see any income from the plan you propose. If you're reimbursed for your costs at less than the business rate you wouldn't have a deduction (as the charitable rate is $0.14/mile), but that still doesn't make any reimbursement under the business rate to be treated as income.
