The bridge was designed and built by Dorman Long and Co Ltd, Middlesbrough Teesside and Cleveland Bridge, Darlington, County Durham and opened in 1932. Until 1967 it was the city's tallest structure.^{[citation needed]} According to Guinness World Records, it is the world's widest long-span bridge   and it is the tallest steel arch bridge, measuring 134 metres (440 ft) from top to water level. It is also the fifth-longest spanning-arch bridge in the world.

Structure

The southern (CBD) bridge end is located at Millers Point in The Rocks area, and the northern end at Milsons Point in the lower North Shore area. It carries six lanes of road traffic on its main roadway, two lanes of road traffic (formerly two tram tracks) and a footpath on its eastern side, and two railway tracks and a bicycle path along its western side, being 305 mm (12 in) broader than the east side.

The main roadway across the bridge is known as Bradfield Highway, Sydney, and is about 2.4 kilometres (1.5 mi) long, making it one of the shortest highways in Australia. (The shortest, also called the Bradfield Highway, is found on the Story Bridge in Brisbane).

The Sydney Harbour Bridge is not completely stationary. It can rise or fall up to 18 cm (7.1 in) depending on whether it is hot or cold because the steel expands or contracts.  

Arch

The arch is composed of two 28-panel arch trusses; their heights vary from 18 m (59 ft) at the centre of the arch to 57 m (187 ft) at the ends next to the pylons.

The arch has a span of 503 m and its summit is 134 m (440 ft) above mean sea level; however, expansion of the steel structure on hot days can increase the height of the arch by as much as 18 cm (7.1 in). Large steel pins support each end of the arch, allowing it to rotate to accommodate expansion and contraction caused by changes of temperature and avoiding stresses that would otherwise cause damage.

The total weight of the bridge is 39,006 tonnes (38,390 long tons). About 79% of the steel came from Middlesbrough, in the northeast of England; the rest was Australian-made. The bridge is held together by six million hand-driven rivets ^[4] that were made at the Park Bridge Ironworks in Lancashire, England. ^{[citation needed]} The steel was tested in Bilston, West Midlands, at the then Alfred Hickman Steelworks by George Scarrot, test house manager and one of the first metallurgists, before being sent to Australia.

Pylons

At each end of the arch stand a pair of 89 m (292 ft) high concrete and granite pylons. The pylons were designed by the Scottish architect Thomas S. Tait     a partner in the architects' firm John Burnet & Partners.   The granite was quarried at Moruya, New South Wales, 314 kilometres (195 mi) south of Sydney. The concrete used was also Australian-made. Abutments, that are essential to support the loads from the arch and hold its span firmly in place, also provide a base for the pylons.

The pylons have no structural purpose; they are there to provide a frame for the arch panels and give better visual balance to the bridge. The pylons were not part of the original design and were added to allay public concern about structural integrity of the bridge. 

Although originally added to the bridge for their aesthetic value, all four pylons have now been put to use: the southeastern pylon contains a museum and tourist centre with a lookout of the harbour; the southwestern pylon is used by the New South Wales Roads and Traffic Authority (RTA) to support its CCTV cameras overlooking the bridge and the roads around that area; the two pylons on the north shore are venting chimneys for fumes from the Sydney Harbour Tunnel; the base of the southern pylon contains the RTA maintenance shed for the bridge, and the base of the northern pylon contains the traffic management shed for tow trucks and safety vehicles used on the bridge.

On New Year's Eve, the numbers for the countdown appear on the pylons of the bridge.