Running wheels which enable the end carriages to travel on the longitudinal gantry girders or runway, and the crab or jenny, which carries the hoisting mechanism, and moves across the span on FIG.
The roadway girders are lattice, 17 ft.
The lattice girders of the side spans were first rolled into place, so as to project some distance beyond the piers, and then the arch ribs were built out, being partly supported by wire-rope cables from (3) Draw or Bascule Bridges.
In closed position the main girders rest on a bed plate on the face of the pier 4 ft.
From 1880 onwards) it has wholly superseded the latter except for girders of less than 100 ft.