During the construction of the second road bridge, the construction of a railway through Perth's southern suburbs to Rockingham and Mandurah became a political issue.
The incumbent Liberal state government proposed building a railway from Kenwick to connect to the Kwinana Freeway, running in the centre of the freeway for only part of its journey.
The Labor opposition instead wanted to build the railway across the Narrows Bridge and down most of the length of the freeway.

After the Labor party won the 2001 state election, it reversed the previous government's position and started planning for the installation of railway tracks across the Narrows Bridge.
The construction of a third bridge was needed due to the lack of previous planning provisions when the second bridge was constructed.
Leighton Constructions won the contract to build the freeway stage of the railway line and set about constructing a narrow southbound railway bridge in the 6-metre (20 ft) gap between the existing road bridges.
The designers of "Package E" of the Southern Suburbs Railway (which included the Narrows Rail Bridge) were GHD, Coffey Geosciences and Wyche Consulting.
The eastern side of the existing northbound (2001) bridge was also strengthened to accommodate the northbound railway track.
Construction was due to start in July 2005 and completion was expected by December 2005.
The first passengers traversed the Narrows on 23 December 2007 with the opening of the Mandurah Railway Line.

The railway bridge deck was made from nine steel girders each weighing up to 99.5 tonnes (219,000 lb) and up to 54 metres (177 ft) long.
These girders were built in Kwinana, brought to the site by road and lowered into position with a crane.
During the construction of the second road bridge, the construction of a railway through Perth's southern suburbs to Rockingham and Mandurah became a political issue. The incumbent Liberal state government proposed building a railway from Kenwick to connect to the Kwinana Freeway, running in the centre of the freeway for only part of its journey. The Labor opposition instead wanted to build the railway across the Narrows Bridge and down most of the length of the freeway.
After the Labor party won the 2001 state election, it reversed the previous government's position and started planning for the installation of railway tracks across the Narrows Bridge. The construction of a third bridge was needed due to the lack of previous planning provisions when the second bridge was constructed. Leighton Constructions won the contract to build the freeway stage of the railway line and set about constructing a narrow southbound railway bridge in the 6-metre (20 ft) gap between the existing road bridges. The designers of "Package E" of the Southern Suburbs Railway (which included the Narrows Rail Bridge) were GHD, Coffey Geosciences and Wyche Consulting. The eastern side of the existing northbound (2001) bridge was also strengthened to accommodate the northbound railway track. Construction was due to start in July 2005 and completion was expected by December 2005. The first passengers traversed the Narrows on 23 December 2007 with the opening of the Mandurah Railway Line.
The railway bridge deck was made from nine steel girders each weighing up to 99.5 tonnes (219,000 lb) and up to 54 metres (177 ft) long. These girders were built in Kwinana, brought to the site by road and lowered into position with a crane.
Narrows Bridge (Perth)