Transit and commuter facilities are likely to be located in congested downtowns or other urban areas, where there is little room for unrestricted layouts. Existing roads, highways, mainline rail and transit tracks, existing structures, and terrain necessitate ingenuity and coordinated decision-making on the alignment and layout of new lines or the expansion of existing lines. Aerial structures are often the preferred alternative and sometimes the only solution to project constraints.
The
utilization of precast, cast-in-place, pretensioned, or post-tensioned
concrete designs lead to durable, economical, and beautiful aerial
structures. Recent aerial structure technologies have been used
in successful transit projects across the country. The application
of truss-erected segmental precast box girder guideway construction
for both the JFK AirTrain Project in New York, NY and the Millenium
Line SkyTrain Extension Project in Vancouver, British Columbia,
Canada resulted in easily erected aerial structures that were completed
on time and within budget.