ll surface vehicular and pedestrian traffic. All structures were left in
place with the exception of the pipes, most of which were temporarily cut
out. The 48-in. brick sewer in the center of Ninth Avenue was broken, and
the sewage was pumped across the excavation through a smaller pipe.

The general method adopted was as follows: The east and west sides of the
avenue were closed, vehicular traffic was turned into the center, and a
trestle for pedestrians was constructed west of the westerly elevated
railway columns. All structures were then supported on transverse girders,
running across the avenue, below the surface, and these rested on concrete
piers on the central rock core. The sides of the avenue were then excavated
to sub-grade, and the permanent steel viaduct was erected on both sides of
the avenue as close as possible to the central rock core. The weight of all
structures was then transferred to the permanent steel viaduct, erected on
the sides of the avenue, by timber bents under the transverse girders
resting on the permanent steel viaduct, and all weight was thus taken off
the central rock core. This core was then excavated to sub-grade, the
permanent viaduct was completed, and all structures were placed on its
deck, using concrete piers and timber bents.

The design and erection of the permanent steel viaduct and the permanent
foundations on its deck were done under another contract, apart from the
North River Division work, and are not described in this paper.

_Elevated Railway Structure of the Interborough Rapid Transit
Company._--The Ninth Avenue Elevated Railway was built between 1877 and
1880 as a two-track structure, the design being such as to permit a third
or central track to be added later, and this was built in 1894. It is
supported on columns under the outside tracks, about 43 ft. from center to
center longitudinally and 22 ft. 3 in. from center to center transversely,
the central track being carried by transverse girders between the columns.

The columns carrying the structure are of fan top design, with the points
of bearing near the extremities at the top; each of the outside tracks is
supported on two longitudinal latticed girders and the central track on
two plate girders; between the columns, transverse girders are spliced to
the outside track cross-frames, and carry the central track system. It was
not thought desirable to put brackets on the columns near the street level
to support the