36 C.F.R. § 910.70 Vault.
Title 36 - Parks, Forests, and Public Property
A vault means an enclosure of space beneath the surface of the public space or sidewalk setback, except that the term vault shall not include public utility structures.
Title 36: Parks, Forests, and Public Property
PART 910—GENERAL GUIDELINES AND UNIFORM STANDARDS FOR URBAN PLANNING AND DESIGN OF DEVELOPMENT WITHIN THE PENNSYLVANIA AVENUE DEVELOPMENT AREA
Subpart D—Glossary of Terms
§ 910.70 Vault.