How about trying the report called Expense Reports - Expenses and Reimbursements.
Then in the selection criteria use value 3 for the expense type (or look at the value help for Mileage Reimbursement Rates). Make sure the rows you need are in the layout and click Go.
This doesn't give miles traveled but if you have the reimbursed amount and you know the reimbursement rate, you could do an easy calculation for miles.
It may be more difficult to calculate if statutory rates are used.