If most people would drive the distance, then you may claim mileage with no further explanation. However, if most people would fly and you are choosing to drive for personal reasons (i.e., sightseeing, stopping off to visit friends, taking family along, etc.), you should expect to be reimbursed the lesser of mileage based on the most direct route or an amount equal to the cost of flying coach or economy with advance booking. If you are driving for business reasons (i.e., transporting large boxes of research equipment), please provide a written statement explaining the circumstances. The basic expectation is that you will get to your business destination using the most economical and reasonable method.