Maryland Code, Transportation § 7-704

(a) The creation of the Administration and the carrying out of its purposes are in all respects for the benefit of the people of this State and the District and for a public purpose, and the activities of the Administration are essential governmental functions.

(b) Except for water and sewer charges imposed by this State or any of its agencies or political subdivisions, the Administration, its activities, and the property it owns or controls are exempt from all taxes, assessments, and charges, whether State or local, now or subsequently levied or imposed.