Except as provided in subsection (b) of this section, the county where the project is located shall maintain every stormwater management system and part of every system that: was constructed by the Commission or the county or accepted for maintenance by the Commission or the county; and is located in a street, an alley, a public way, or a public space. Unless the county agrees otherwise: a stormwater management system that is located on real property owned by the Maryland–National Capital Park and Planning Commission shall be maintained by the Maryland–National Capital Park and Planning Commission; and a stormwater management system or facility that is located in a road maintained by the State Highway Administration shall be maintained by the State.