Narrows Bridge

About

The Narrows Bridge is a freeway and railway crossing of the Swan River in Perth, Western Australia. Made up of two road bridges and a railway bridge constructed at a part of the river known as the Narrows, located between Mill Point and Point Lewis, it connects the Mitchell and Kwinana freeways, linking the city's northern and southern suburbs. The original road bridge was opened in 1959 and was the largest precast prestressed concrete bridge in the world. Construction of the northern interchange for this bridge necessitated the reclamation of a large amount of land from the river. The bridge formed part of the Kwinana Freeway which originally ran for only 2.4 miles (3.9 km) to Canning Bridge. Over the following decades, the freeway system was expanded to the north and south, greatly increasing the volume of traffic using the bridge. As a result, in 2001, a second road bridge was opened to the west of the original bridge, and in 2005, the railway bridge was constructed in the gap between the two traffic bridges. Passenger trains first traversed the Narrows in 2007 with the opening of the Mandurah railway line.

The close distance between Mill Point and Point Lewis at the foot of Mount Eliza meant the site was suggested as a suitable location for a bridge as early as 1849. A bridge was proposed for the site in 1899, but its expected cost of £ 13,000 was deemed too high. Preliminary planning for a bridge at the site finally began in 1947, but was suspended so that a replacement for The Causeway could be built at Heirisson Island, at the city's eastern end. The new Causeway bridges were opened in 1952, and by 1954 traffic using them to enter the city had doubled, renewing calls for a bridge at the Narrows.

Site investigations for the bridge began in August 1954. The bridge was proposed for the Narrows site by the Town Planning Commission under the chairmanship of Harold Boas. The chosen site drew public protest on the basis that the bridge would spoil the view to and from the city. Also, residents of the wealthy Mill Point area were angry that they would have a major highway running beside their houses. The site also necessitated the reclamation of 60 acres (24 ha) of land from Mounts Bay for the bridge approach and interchange. This land reclamation, which started in October 1954, saw the addition of 3.4 million cubic metres (4.5 million cubic yards) of sand, much of which was dredged from Melville Water.

The state started saving for the new bridge in September 1954, and the construction of the bridge was approved by the Hawke state Labor government in November 1954, before the Hepburn-Stephenson metropolitan roads plan had been finalised, such was the urgency of a new traffic link. The construction of the bridge was subsequently endorsed in the 1955 Hepburn–Stephenson plan, which later developed into the Metropolitan Region Scheme.

The river bed at the site of the proposed bridge was not ideal for bridge building, with soft mud extending down as deep as 80 feet (24 m) and sand beds below that going a further 40 feet (12 m) down. Ernie Godfrey, a bridge engineer with the Main Roads Department, travelled overseas to inspect bridges in similar geological locations and to source a designer for the proposed bridge. The design contract for the bridge was won by British engineering firm Maunsell & Co.

Construction on the road system began in 1956, and the contract for construction of the bridge was signed by Commissioner of Main Roads J. Digby Leach on 16 March 1957. The bridge was built by Danish firm Christiani & Nielsen in conjunction with Western Australian engineering firm J. O. Clough & Son. Leif Ott Nilsen oversaw construction on behalf of Christiani & Nielsen. The first timber pile for the temporary staging for the construction was driven at noon on 8 June 1957. The first permanent pile for the bridge was driven home on 18 August 1957. Work on the bridge's precast concrete beams began in September 1957, and the first of these was lifted into place by the 60-foot (18 m) gantry crane in February 1958. The last river pile was driven home in November 1958, and the final concrete beam was lowered into position in June 1959. During construction on 10 February 1959, John Tonkin, then the Deputy Premier and Minister for Works, announced that the new bridge was to be named the Golden West Bridge. However, Golden West was also the name for a popular soft drink ; the proposal encountered scorn from commentators and was quietly dropped.

The bridge cost £A 1.5 million, equivalent to A$ 51.8 million in 2022, as part of a wider road system costing £3.5 million. Construction of the bridge took two years and five months. It was officially opened by Governor Charles Gairdner on 13 November 1959. He unveiled a plaque on the bridge together with Premier David Brand, Commissioner of Main Roads J. Digby Leach and Works Minister Gerald Wild. Gairdner was also the first person to drive across the new bridge. It was hoped at this stage that the debt raised to pay for the bridge would be repaid by the Government within 12 months.

The bridge formed part of the new Kwinana Freeway, which originally ran 2.4 miles (3.9 km) from the Narrows to Canning Highway. This was described as the "most modern highway" in Western Australia, with a speed limit of 50 miles per hour (80 km/h). The bridge was also the largest precast prestressed concrete bridge in the world at the time of its opening.

The bridge was jointly designed by engineering firm G. Maunsell & Partners and architects William Halford & Partners. The prestressed concrete design was relatively new for Western Australia, where road bridges had traditionally been built from timber frameworks. The bridge is arched along its length, with a vertical curve of up to 4% grade.

The unusually soft soil conditions at the site forced the use of 160 "Gambia piles" for the bridge's foundations, named after the country in which they were first used. The 31-inch (79 cm) diameter piles have steel shells and conical noses. The hollow piles were driven by a drop hammer falling within them, then when they had sufficient resistance to driving, they were filled with reinforced concrete.

The piles support two river piers, two shore piers and two abutments. The bridge's support columns on the piers were designed in a triangular form, larger at the top than at the bottom, each carrying two of the bridge's beams, so as to not completely obstruct the view through the bridge's piers. These columns support the bridge's five spans: a central span of 320 feet (98 m), two flanking spans of 230 feet (70 m) each and two smaller spans of 160 feet (49 m) at each end passing over roadways. The bridge has eight parallel lines of beams. Each line of beams consists of two cantilever spans 370 feet (110 m) long suspended between the shore and river piers, a central suspended span 140 feet (43 m) long between the two river piers, and two 110-foot (34 m) spans suspended over roadways at either end. Suspended between the beams of the bridge were 1 mile (1.6 km) of 30-inch (76 cm) water mains pipes and 0.5 miles (800 m) of 10.5-inch (27 cm) gas and drainage pipes.

Footpaths 8 feet (2.4 m) wide on either side of the bridge were formed by concrete cast in situ and cantilevered out from the adjacent beams. These footpaths were separated from the roadway and the bridge's edge by lightweight aluminium balustrades and safety fences installed by Bristile. The street lights were integrated into the safety fence.

The deck of the bridge was formed by pre-casting individual concrete units on the southern river shore, then hoisting them into place on temporary timber staging in the river. The units were then structurally joined by strands of high-tensile wire and stretched with a hydraulic jack. These pre-stressing strands were anchored in reinforced concrete blocks at the ends of the spans. The new bridge had a traffic capacity of 6,000 cars per hour in each direction, over a total of six traffic lanes.

Strengthening works were carried out on the bridge by Structural Systems Ltd in 1996. Also in 1996, decorative night lighting was installed on each side of the bridge. The bridge was entered on the state's heritage register on 8 January 1999, and was named a national engineering landmark by the Institution of Engineers, Australia, in November 1999.

The opening of the southern regions of Perth to easier CBD access changed the nature of the metropolitan area, prompting dramatic population growth south of the river. This led to increased traffic on the bridge, causing regular traffic jams in peak hour. Over the years, governments suggested various ideas to reduce the traffic using the bridge, including introducing congestion pricing similar to that used in Singapore, charging vehicles to enter the central business district during peak periods. The government also encouraged voluntary car sharing. These efforts were largely unsuccessful, and by the 1990s, the bridge had become the city's worst traffic bottleneck, despite the addition of an extra traffic lane, bringing the total number of lanes to seven:

Peak-hour users of the freeway have become accustomed to driving into a bottle-neck every day. They also know that it takes only a minor bingle on the bridge to turn the freeway into a vast parking lot, inciting road rage symptoms and making thousands of people late for work.

— Journalist Andre Malan, The West Australian, 7 March 1998

The bridge was jointly designed by engineering firm G. Maunsell & Partners and architects William Halford & Partners. The prestressed concrete design was relatively new for Western Australia, where road bridges had traditionally been built from timber frameworks. The bridge is arched along its length, with a vertical curve of up to 4% grade.

The unusually soft soil conditions at the site forced the use of 160 "Gambia piles" for the bridge's foundations, named after the country in which they were first used. The 31-inch (79 cm) diameter piles have steel shells and conical noses. The hollow piles were driven by a drop hammer falling within them, then when they had sufficient resistance to driving, they were filled with reinforced concrete.

The piles support two river piers, two shore piers and two abutments. The bridge's support columns on the piers were designed in a triangular form, larger at the top than at the bottom, each carrying two of the bridge's beams, so as to not completely obstruct the view through the bridge's piers. These columns support the bridge's five spans: a central span of 320 feet (98 m), two flanking spans of 230 feet (70 m) each and two smaller spans of 160 feet (49 m) at each end passing over roadways. The bridge has eight parallel lines of beams. Each line of beams consists of two cantilever spans 370 feet (110 m) long suspended between the shore and river piers, a central suspended span 140 feet (43 m) long between the two river piers, and two 110-foot (34 m) spans suspended over roadways at either end. Suspended between the beams of the bridge were 1 mile (1.6 km) of 30-inch (76 cm) water mains pipes and 0.5 miles (800 m) of 10.5-inch (27 cm) gas and drainage pipes.