26 CFR § 49.4263-1 - Commutation tickets.
(a)Tickets for single trips of less than 30 miles. Amounts paid for commutation or season tickets or books for single trips of less than 30 miles are exempt from the tax imposed by section 4261, regardless of the length of time for which such tickets or books are valid. The phrase “less than 30 miles” means less than 30 constructive miles in instances where the charge is based on constructive mileage.
(b)Tickets for one month or less. Amounts paid for commutation tickets or books for one month or less are exempt from the tax regardless of the distance of a single trip.