41 C.F.R. § 301-10.452

Employees are responsible for any additional costs resulting from using a Government-funded commercial rental automobile for other than official purposes. Official purposes which include transportation:

(a) Between places of official business;

(b) Between such places and places of temporary lodging when public transportation is unavailable or its use is impractical; or

(c) Between either paragraph (a) or (b) of this section and restaurants, drug stores, barber shops/hair stylists, places of worship, cleaning establishments, and similar places necessary for the sustenance, comfort, or health of the employee to foster the continued efficient performance of Government business.