thumb|Chaining numbers can be seen on the black pillars in the middle of the tracks of [[West Fourth Street–Washington Square (IND Eighth Avenue Line)|West Fourth Street–Washington Square.]]

New York City Subway chaining is a method to precisely specify locations along the New York City Subway lines. It measures distances from a fixed point, called chaining zero, following the twists and turns of the railroad line, so that the distance described is understood to be the "railroad distance," not the distance by the most direct route ("as the crow flies").

The New York City Subway system differs from other railroad chaining systems in that it uses the engineer's chain of rather than the surveyor's chain of .

Terminology

Chaining zero

Chaining zero is a fixed point from which the chaining is measured on a particular chaining line. A chaining number of, for example, 243 at a specific line location (called a chaining station) identifies that the location is the length of 243 100-foot chains () from chaining zero, usually measured along the center line of the railroad.

Once chaining is established, it is rare but not unheard of to change the location of chaining zero or the route along which it is measured on a given line. There are several examples of chaining numbers that refer to a chaining zero location that no longer exists or along a physical line that no longer exists, because of abandonment or demolition. Notable among these are several existing chaining lines that originated near New York City Hall via the Brooklyn Bridge, discontinued since 1944. It is occasionally possible for a reroute to alter the accuracy of chaining numbers slightly.

Exceptions exist to the principle that chaining numbers represent a railroad distance to the zero point. On the original IND chaining zero for the original system is a political rather than physical location, and there is no railroad at or near the zero point.

| Far Rockaway–Mott Avenue

  • IND E: From Bergen Street to Fulton Street, the line is tied to IND A, which it shares with the Hoyt–Schermerhorn Streets station. North of Fulton Street, the line is reverse-tied to IND D.
  • IND F/FA: The Rockaway Line was originally part of the Long Island Rail Road and was chained from Long Island City station in Long Island City, Queens, via the old Montauk Line. When the IND acquired the Rockaway Line south of Liberty Avenue in 1956, it preserved the LIRR chaining distances. The single-track connection between the east and west legs of Hammels Wye has its own chaining, which starts at the point it branches from the east leg.
  • IND K: The Liberty Avenue Elevated, currently part of the IND Fulton Street Line, was originally the eastern portion of the BMT Fulton Street Line, which had its chaining zero at Park Row. When the IND acquired the Liberty Avenue structure, it preserved the BMT chaining letter and zero point, reverse-tying the chaining back to Euclid Avenue.
  • IND S: Ties to IND T near 2nd Avenue and 63rd Street, where the two lines intersect.

IRT

Current

All Mileage zeroes are at New Lots Avenue, except for the IRT Flushing Line, whose zero is Times Square.

| Flushing–Main Street IRT Y has since been tied to IRT W under a new signal contract.

  • Broadway/44th Street: The point where the Dual Contracts section of the Broadway–Seventh Avenue Line (from Times Square–42nd Street south) meets the Contract I section (north of 42nd Street).
  • Park Avenue/38th Street: The point where the Dual Contracts section of the Lexington Avenue Line (from Grand Central–42nd Street north) meets the Contract I section (south of 42nd Street).

Explanatory notes

References

  • JoeKorNer - New York City Subway Chaining