Spit Bridge

History

Sydney's Lower North Shore and Northern Beaches were serviced by a punt operating from The Spit since the late nineteenth century up until 1924.

In 1924, The (first) Spit Bridge was completed and opened. By 1927 the timber low–level bridge saw a 60% growth over that of the punt for the year prior to the bridge opening. The amount of traffic using the bridge was higher than expected and the subsequent revenue from tolls providing a financial boon for the government. Various plans were considered to reduce congestion including a high-level bridge and a bridge further upstream, leaving the existing bridge for local traffic; however none were enacted until after World War II. The NSW Government decided to build another low–level bridge at the same site.

Description

Construction of the current bridge had commenced in 1952 and after delays was completed in 1958; and opened on 19 November 1958.

The Spit Bridge over Middle Harbour can be described as a steel and concrete girder bridge with a bascule lift span. The Spit Bridge comprises 7 spans of a total length of 745 feet 6 inches (227.23 m), has four traffic lanes with a width of 44 feet (13 m) and a pedestrian walkway of 5 feet (1.5 m) on either side. There are three spans at either end of the opening span. Each of the six fixed spans have four welded plate girders as the main members, with cross girders, but without stringers or horizontal bracing. The concrete deck is dowelled to the steelwork. The opening span (Span 4) is a single-leaf bascule. It has two main girders, with cross girders and stringers, covered by an open mesh steel deck.

The two footways are of concrete on the fixed spans, and steel on the bascule span. The piers either side of the opening span are flanked by fenders, and when the bridge is in the open position a navigation channel of 80 feet (24 m) wide is created. At the Mosman end the slab and two column piers rest on concrete piles driven into to the sands of the harbour bed at a depth of between 40 and 50 feet (12 and 15 m). At the Manly end the harbour bottom slopes up steeply to outcropping rock on which the northern abutment sits. Piers 5 and 6 are double cylinder piers sitting on bedrock below the harbour bed. The main pier which supports the bascule span is Pier 4. It rests on four cylinders taken down to sandstone bedrock at a depth of between 45 to 75 feet (14 to 23 m) which is 75 and 105 feet (23 and 32 m) below mean sea level. The pier is box-like and supports all machinery for the operation of the bascule, including the operator's cabin. The approaches and abutments at each end are varied due to the nature of the topography. The southern abutment is built up from the sandy beach level and has a retaining wall faced with stone on either side. The northern abutment is resting directly on the rock on the western side and is built up on the eastern side with a retaining wall. Due to the variation in ground level on each shore there is a grade of 2.68% from south to north. Traffic across the bridge is regulated by traffic lights at either end (located at the end of Spans 2 and 6) and by roadway gates which operate as the bridge is about to open.

The bridge has two traffic lanes in each direction, with a tidal flow system established, while the approaches to it have three lanes in each direction.

Alternative replacement options

The original plans for the Warringah Expressway were for it to be an above-ground freeway that would cross Middle Harbour between Castlecrag and Seaforth, joining the current Warringah Expressway, Wakehurst Parkway (which was to have been upgraded to a dual carriageway road) and the Burnt Bridge Creek Deviation. It was planned by the former Liberal member for Pittwater and Premier Askin and was to have been completed by 1980. The Labor government, led by Neville Wran, shelved these plans with their "No Freeways" policy.

The Spit Bridge forms part of the route from the Sydney central business district and Lower North Shore suburbs to Manly and the Northern Beaches. The next crossing is some distance upstream (north-west) at Roseville Bridge. The Roads and Traffic Authority announced in August 2006 that tenders had been called for widening of the bridge to six lanes, with two extra traffic lanes and a pedestrian/cycleway being added on the western side, and upgrades to the lifting mechanism. Construction was to have begun in 2007, however, the project was scrapped in May of that year. According to the government this was due to technical and engineering difficulties, according to the opposition it was because of political considerations. The increased cost estimates to $115m were deemed to be not justifiable by the Minister for Roads Eric Roozendaal and the five–year plan was abandoned. Traffic delays either side of The Spit Bridge have been a problem for many years, not only on the approaches to the bridge itself, but also far up the hills on either side. Proposals to ameliorate delays have included widening the bridge, a tunnel linking the Warringah Expressway and the Burnt Bridge Creek Deviation, and a high-level bridge in place of the existing one. David Barr, the member for Manly, claimed in 2002 that the latter two were too expensive with $200 million estimated for a high-level bridge, and $1 billion for the tunnel.

In 2007, the Roads and Traffic Authority found that traffic either side of the bridge doesn't return to normal for 15 minutes after the bridge is opened and reduced the number of bridge opening times.

In 2014, Premier Mike Baird, also the member for Manly, announced plans to bypass Mosman and The Spit Bridge by constructing a $2–3 billion tunnel from Seaforth to Neutral Bay that would run underground beneath Military Road.