The towers have columns consisting as a rule of a 16 x 7/16-inch web plate and four 6 x 4 x 5/8-inch bulb angles.  The horizontal struts in their cross-bracing are made of four 4 x 3-inch angles, latticed to form an I-shaped cross-section.  The X-bracing consists of single 5 x 3-1/2-inch angles.  The tops of the columns have horizontal cap angles on which are riveted the lower flanges of the transverse girders; the end angles of the girder and the top of the column are also connected by a riveted splice plate.  The six longitudinal girders are web-riveted to the transverse girders.  The outside longitudinal girder on each side of the viaduct has the same depth across the tower as in the connecting span, but the four intermediate lines are not so deep across the towers.  In the single trestle bents the columns are the same as those just described, but the diagonal bracing is replaced by plate knee-braces.

The Manhattan Valley Viaduct on the West Side line, has a total length of 2,174 feet.  Its most important feature is a two-hinged arch of 168-1/2 feet span, which carries platforms shaded by canopies, but no station buildings.  The station is on the ground between the surface railway tracks.  Access to the platforms is obtained by means of escalators.  It has three lattice-girder two-hinge ribs 24-1/2 feet apart on centers, the center line of each rib being a parabola.  Each half rib supports six spandrel posts carrying the roadway, the posts being seated directly over vertical web members of the rib.  The chords of the ribs are 6 feet apart and of an H-section, having four 6 x 6-inch angles and six 15-inch flange and web plates for the center rib and lighter sections for the outside ribs.  The arch was erected without false work.

[Illustration:  SHOWING CONCRETE OVER IRON WORK—­HARLEM RIVER TUNNEL]

The viaduct spans of either approach to the arch are 46 to 72 feet long.  All transverse girders are 31 feet 4 inches long, and have a 70 x 3/8-inch web plate and four 6 x 4-inch angles.  The two outside longitudinal girders of deck spans are 72 inches deep and the other 36 inches.  All are 3/8-inch thick and their four flange angles vary in size from 5 x 3-1/2 to 6 x 6 inches, and on the longest spans there are flange plates.  At each end of the viaduct there is a through span with 90-inch web longitudinal girders.

Each track was proportioned for a dead load of 330 pounds per lineal foot and a live load of 25,000 pounds per axle.  The axle spacing in the truck was 5 feet and the pairs of axles were alternately 27 and 9 feet apart.  The traction load was taken at 20 per cent. of the live load, and a wind pressure of 500 pounds per lineal foot was assumed over the whole structure.

[Sidenote:  Tubes under Harlem River]