Designed and constricted to support steel wheeled, steel rail train vehicles and track systems, elevated rail structures are the most massive and expensive of transportation facilities. While subway tunnels and subterranean stations are more costly to construct, much of their construction expenditures are associated with tunneling, excavation and reinforcement of underground facilities.
Construction of elevated rail structures and stations capable of supporting trains weighing over 100,000 pounds per car requires design and structures resembling elevated highways and freeway transition lanes. And, the term “light rail”, attributed to most at grade rail systems, describes their relative passenger capacity, rather than the weight of rail cars or the structures built to support them. Similar to the building of elevated highways and freeways, the construction of elevated railways often involves years of heavy, disruptive construction activity, extending across miles of existing urban and suburban settings. Extensive mitigation measures required to lessen the negative impacts of the construction process give way to permanent mitigation measures and construction required for reduction of the impacts of train operation on the elevated railway structures. Miles of sound walls are often required to buffer the noise imposed on adjacent settings along elevated rail routes.
Beyond their construction process, the size and mass of elevated rail supporting structures occupy such space that they monopolize any location in which they are built. The paths of such elevated rails structures tend to be dominated by their pylons and other supporting structures such that all pre-existing development, street and activity patterns are permanently altered or eliminated. As intrusive and permanently altering of localized property, development patterns, street networks and environmental settings as elevated rail structures can potentially be, they can divide once cohesive neighborhoods and activity networks in ways that freeway construction once carved up urban communities and open space.