§ 301-4.1 - Basic rules.

(a) Mileage payments. When employees and others rendering service to the Government use privately owned motor vehicles or airplanes in the conduct of official business within or outside their designated posts of duty or places of service and such use is authorized or approved as advantageous to the Government or as an authorized or approved exercise of the employee's preference, payment shall be made on a mileage basis unless payment on an actual expense basis is specifically authorized by law.

(b) Distance measurements—(1) Automobile and motorcycle travel. When transportation is authorized or approved by privately owned motorcycles or automobiles, distances between points traveled shall be as shown in standard highway mileage guides or actual miles driven as determined from odometer readings. (Actual odometer readings need not be shown on the travel voucher.) Any substantial deviations from distances shown in the standard highway mileage guides shall be explained. The mileage rate as authorized or approved may be paid from whatever point the employee or other person rendering service to the Government begins his/her journey.

(2) Airplane travel. The air mileage between the origin and destination airports, as determined from airways charts issued by the National Oceanic and Atmospheric Administration, Department of Commerce, shall be reported on the reimbursement voucher and shall be used in computing payment for the use of a privately owned airplane. If a detour was necessary because of adverse weather, mechanical difficulty, or other unusual conditions, the additional air mileage may be included in the mileage reported on the reimbursement voucher and, if included, it must be explained. When an official requirement for deviation from direct route travel is such that airway mileage charts are not adequate to determine mileage, the formula of flight time multiplied by cruising speed of the airplane may be the basis for mileage determinations.

(c) Other allowable costs. Reimbursement for parking fees; ferry fees; bridge, road, and tunnel fees; and airplane parking, landing, and tiedown fees shall be allowed in addition to the mileage allowance unless the travel orders or other administrative determinations restrict such allowance.