Mileage--Travel by Privately-Owned Automobile--Between Residence and Headquarters--Official Duty En Route

The Civil Service Commission requested GAO's opinion on the following questions relating to the computation of mileage for use of personally-owned automobiles by Civil Service Commission investigations: (1) (a) Is it required that a deduction representing twice the distance between residence and headquarters building be made for every day on which an investigator performs any duty in his headquarters city? (b) If so, is it proper to deduct only the cost of public transportation in the cases where public transportation would be used in actually going to and from the headquarters office? (c) If deduction has been made for a particular day, is another deduction required if the investigator performs overtime duty, compensated or uncompensated, in the evening? (2) (a) Is any deduction required on days on which all the investigator's work is performed outside the limits of the headquarters city? (b) Does the fact that the investigator lives inside or outside the city, or may travel through a part of the city in going from one interview to another, make any difference? and (3) If deduction is not required merely because an investigator performs some duty in the headquarters city, is it required on days on which he actually comes in to the office as described?