Philadelphia–Lindenwold High-Speed Line Surveys

A main base line (monumented center line) of tangents and simple curves, separate from track geometry with its profusion of spirals, is a practical necessity for a Rapid Transit project. It permits coordinated design and construction layout. Track alignment can be revised to fit specific conditions without changing the general construction base line. A modified second order survey, such as 1:15,000, is preferred for high speed transit projects. Strategic control points of base lines, and their references, should be permanently located on existing structures where possible, by the use of concrete monuments or iron pins where necessary. Preservation of control point references by contractors is especially important when there are following contractors. Early location of right of way lines, and tieing them to the main base line can prevent costly encroachment by fences and drainage structures. The various surveys, aerial photography control, design, right of way, construction, and as-builts are described.