As used in this part:
(a) “Project” means an overpass, underpass, or tunnel, or any combination thereof, at a single crossing, the planning, construction and maintenance of which is authorized by this part.
(b) “District” means separation of grade district.
(c) “County” means the county in which the district or proposed district is situated.
(d) “Board” means board of supervisors of the county in which the district or proposed district is situated.
(e) “Commission” means the commission provided in Chapter 3 of this part.