41 C.F.R. § 301-10.190

Employees may use a transit system as a means of transportation in conjunction with official travel when such transportation is authorized and approved by the agency in the following manner:

(a) At the official station.

(1) From the employee's residence or other authorized point of departure, e.g., rail to airport;

(2) To the employee's residence or other authorized point of return, e.g., airport to rail;

(3) From the employee's residence to the office on the day of departure from the official station on official TDY that requires at least one night's lodging; or

(4) From the office to the employee's residence on the day of return to the official station from an official TDY assignment that requires at least one night's lodging.

(b) At the TDY location.

(1) From the TDY transit system station(s) to the place of lodging or place of official business and return;

(2) To, from, and between places of lodging and official business;

(3) Between places of official business; or

(4) To obtain meals at the nearest available place when the nature and location of the official business or the lodging at a TDY location are such that meals cannot be obtained there.