In this way trestles were built half across
the street, strong enough to carry all the street cars and traffic on
that half of the roadway. Cableways to handle the dirt were erected
near the curb line, spanning a number of these trestles, and then the
earth between them was excavated from the curb to within a few feet of
the nearest electric car track. The horse car tracks were removed.
Between the electric tracks a trench was dug until its bottom was
level with the tops of the trestles, about three feet below the
surface as a rule. A pair of heavy steel beams was then laid in this
trench on the trestles. Between these beams and the curb line a second
pair of beams were placed. In this way the equivalent of a bridge was
put up, the trestles acting as piers and the beams as girders. The
central portion of the roadway was then undermined and supported by
timbering suspended from the steel beams. The various gas and water
pipes were hung from timbers at the surface of the ground. About four
sections, or 150 feet, of the subway were built at a time in this
manner. When the work was completed along one side of the street it
was repeated in the same manner on the other side. This method of
construction was subsequently modified so as to permit work on both
sides of the street simultaneously. The manner in which the central
part of the roadway was supported remained the same and all of the
traffic was diverted to this strip.
[Illustration: SUPPORT OF ELEVATED RAILWAY STATION AT 42D STREET AND
SIXTH AVENUE]
Between 14th and 17th Streets, because of the proximity of the rock to
the surface, it was necessary to move the tracks of the electric
surface railway from the center of the street some twenty feet to the
east curb, without interrupting traffic, which was very heavy at all
times, the line being one of the main arteries of the Metropolitan
system.
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