In my research I have found that unless you are an injured employee who is claiming Workers Compensation benefits, your employer does not have to reimburse you for travel expenses. There is no set mileage rate that they must follow, nor are they required by law to pay for business related travel. I have found that most employers do reimburse employees for travel expenses including a rate for mileage incurred when traveling for business. The rates and regulations that they use usually reflect that of the State.
When using a privately owned vehicle there are guidelines and restrictions as to what constitutes business travel and is therefore reimbursable. A driver who leaves the office to conduct business in the field and returns to the office may be reimbursed for all mileage directly connected with the business trip, A driver who leaves home to conduct business and returns home without stopping at the assigned office may be reimbursed for all mileage directly connected with the business trip, which is in excess of the round trip commute miles normally traveled. In no event shall a driver be reimbursed for commuting to and from their assigned office. If however your normal or assigned office is considered your home and you are required to travel to another site than you may be reimbursed for those miles traveled.
If your employer chooses not to reimburse you for the miles that you drive than you may claim it as a deduction. The current federal standard rate is $.445 per mile. If you are given a mileage rate and it is below this amount than you may be able to claim the difference, however if you are paid at a higher rate, the excess may be considered taxable wages. The premium rate in the state of Michigan is to correspond with that of the federal standard.