The scheme is part of preparation work to electrify the South Wales Mainline.
A 600-tonne crawler crane was used to lift and install the new structures deck in the early hours on Saturday, 17 September.
In addition, Maesglas Road Bridge was demolished along with Hawse Lane and Green Lane bridges located in the Marshfield area of Newport as work now commences to reconstruct these structures.
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Cardiff the main span of Beresford Road Bridge in Splott was demolished and work was also completed in the Cardiff Central area, part of the Cardiff Area Signalling Renewal project to modernise the Cardiff and Valleys railway.
Karl Gilmore, programme manager at Network Rail said: "The upgrade work we completed this weekend as part of our Railway Upgrade Plan to deliver a bigger, better railway for passengers was focused on five bridges in Cardiff and Newport.
"This work was a crucial element in preparing the South Wales Mainline for electrification and over 100 of our orange army worked day and night to successfully complete all the vital milestones we set out to achieve over this 56 hour period."
(LM)
