41 C.F.R. § 301-10.7 : Public Contracts and Property Management — FEDERAL TRAVEL REGULATION SYSTEM — TEMPORARY DUTY (TDY) TRAVEL ALLOWANCES — ALLOWABLE TRAVEL EXPENSES —10 - TRANSPORTATION EXPENSES — GENERAL —10.7 - How should I route my travel?
You must travel to your destination by the usually traveled route unless your agency authorizes or approves a different route as officially necessary.