Trunk Line is about studies in infrastructure. So what is infrastructure?
OED:
[Fr. (1875 in Robert), f. INFRA- + STRUCTURE n.]
A collective term for the subordinate parts of an undertaking; substructure, foundation.
substructure: That part which supports something else.
foundation: The solid ground upon which another structure is erected.
(OED usage dates to 1927.)
Encarta Thesaurus:
(1) substructure, organization, structure, setup, arrangement, groundwork, frame, foundation, base
(2) public service, public transport, communications, power supply, water supply, broadcasting, telecommunications, networks, transportation