From the Borough Hall, Manhattan, to the 96th Street station, the line is four-track. On the Fort George branch (including 103d Street station) there are three tracks to 145th Street and then two tracks to Dyckman Street, then three tracks again to the terminus at Bailey Avenue. On the Bronx Park branch there are two tracks to Brook Avenue and from that point to Bronx Park there are three tracks. On the Lenox Avenue spur to 148th Street there are two tracks, on the City Hall loop one track, on the Battery Park loop two tracks. The Brooklyn Extension is a two-track line. There is a storage yard under Broadway between 137th Street and 145th Street on the Fort George branch, another on the surface at the end of the Lenox Avenue spur, Lenox Avenue and 148th Street, and a third on an elevated structure at the Boston Road and 178th Street. There is a repair shop and inspection shed on the surface adjoining the Lenox Avenue spur at the Harlem River and 148-150th Streets, and an inspection shed at the storage yard at Boston Road and 178th Street. [Sidenote: _Length of Line._] The total length of the line from the City Hall to the Kingsbridge terminal is 13.50 miles, with 47.11 miles of single track and sidings. The eastern or Bronx Park branch is 6.97 miles long, with 17.50 miles of single track. [Illustration: PROFILE OF BROOKLYN EXTENSION.] [Sidenote: _Grades and Curves._] The total length of the Brooklyn Extension is 3.1 miles, with about 8 miles of single track. The grades and curvature along the main line may be summarized as follows: The total curvature is equal in length to 23 per cent. of the straight line, and the least radius of curvature is 147 feet. The greatest grade is 3 per cent., and occurs on either side of the tunnel under the Harlem River. At each station there is a down grade of 2.1 per cent., to assist in the acceleration of the cars when they start. In order to make time on roads running trains at frequent intervals, it is necessary to bring the trains to their full speed very soon after starting. The electrical equipment of the Rapid Transit Railroad will enable this to be done in a better manner than is possible with steam locomotives, while these short acceleration grades at each station, on both up and down tracks, will be of material assistance in making the starts smooth. Photograph on page 26 shows an interesting feature at a local station, where, in order to obtain the quick acceleration in grade for local trains, and at the same time maintain a level grade for the express service, the tracks are constructed at a different level. This occurs at many local stations. On the Brooklyn Extension the maximum grade is 3.1 per cent. descending from the ends to the center of the East River tunnel. The minimum radius of curve is 1,200 feet. [Illustration: STANDARD STEEL CONSTRUCTION IN TUNNEL--THIRD RAIL PROTECTION NOT SHOWN] [Illustration: PLAN OF BROOKLYN BRIDGE STATION AND CITY HALL LOOP] [Sidenote: _Track_]