The chief engineer of the line's construction, George Christian Darbyshire, reported in November 1856, that drawings and specifications for the wrought iron bridge over the Saltwater River had been sent to England on 25 June 1856, and that the drawings and specifications for the masonry of the bridge were also well advanced.

[3] The specification for the wrought iron tubular box girder bridge to a design developed and fabricated by William Fairbairn & Sons of Manchester were: " ...one span of two hundred feet in the clear between the piers, and to consist of three wrought iron tubular girders, each of two hundred feet clear span, supported upon two stone piers twenty-one feet six inches above high water level.

The roadway is to be carried upon longitudinal sleepers resting upon, and bolted to the angleirons of the cross bearers.

In 1911, in order to carry the heavier locomotives coming into service, and following the installation of temporary timber props to strengthen the bridge, the spans were replaced with two mild steel through hog-back Pratt trusses, fabricated by Mephan Ferguson.

So that trains could continue to operate over the bridge during the works, the replacement was done by erecting the new trusses inside the existing girders and then removing the latter.