D.C. Mun. Regs. tit. 27, r. 27-3358
Costs for transportation, lodging, meals, and incidental expenses incurred by contractor personnel in official company business related to the District contract shall be allowable. Allowable costs may be based on actual cost incurred, per diem or mileage, or a combination if the method used-does not result in an unreasonable charge.
Travel costs directly attributable to specific contract performance shall be allowable and may be charged to the contract as a direct cost.
Travel costs incurred in the normal course of overall administration of the business shall be allowable and shall be treated as an indirect cost.
The difference in cost between first-class air accommodations and less than first-class accommodations shall not be allowable.
D.C. Mun. Regs. tit. 27, r. 27-3358