Tower Bridge

Tower Bridge (built 1886–1894) is a combined bascule and suspension bridge in London which crosses the River Thames. It is close to the Tower of London, from which it takes its name, and has become an iconic symbol of London.

The bridge consists of two towers tied together at the upper level by means of two horizontal walkways, designed to withstand the horizontal forces exerted by the suspended sections of the bridge on the landward sides of the towers. The vertical component of the forces in the suspended sections and the vertical reactions of the two walkways are carried by the two robust towers. The bascule pivots and operating machinery are housed in the base of each tower. The bridge's present colour scheme dates from 1977, when it was painted red, white and blue for Queen Elizabeth II's silver jubilee. Originally it was painted a mid greenish-blue colour.

The nearest London Underground tube stations are Tower Hill on the Circle and District line, London Bridge and Bermondsey, and the nearest Docklands Light Railway station is Tower Gateway.

In the second half of the 19th century, increased commercial development in the East End of London led to a requirement for a new river crossing downstream of London Bridge. A traditional fixed bridge could not be built because it would cut off access by tall-masted ships to the port facilities in the Pool of London, between London Bridge and the Tower of London.

A Special Bridge or Subway Committee was formed in 1877, chaired by Sir Albert Joseph Altman, to find a solution to the river crossing problem. It opened the design of the crossing to public competition. Over 50 designs were submitted, including one from civil engineer Sir Joseph Bazalgette. The evaluation of the designs was surrounded by controversy, and it was not until 1884 that a design submitted by Sir Horace Jones, the City Architect (who was also one of the judges), was approved.

Jones' engineer, Sir John Wolfe Barry, devised the idea of a bascule bridge with two towers built on piers. The central span was split into two equal bascules or leaves, which could be raised to allow river traffic to pass. The two side-spans were suspension bridges, with the suspension rods anchored both at the abutments and through rods contained within the bridge's upper walkways.

The bridge was officially opened on 30 June 1894 by The Prince of Wales (the future King Edward VII), and his wife, The Princess of Wales (Alexandra of Denmark).

The bridge connected Iron Gate, on the north bank of the river, with Horselydown Lane, on the south – now known as Tower Bridge Approach and Tower Bridge Road, respectively. Until the bridge was opened, the Tower Subway – 400 m to the west – was the shortest way to cross the river from Tower Hill to Tooley Street in Southwark. Opened in 1870, Tower Subway was among the world's earliest underground ('tube') railway, but closed after just three months and was re-opened as a pedestrian foot tunnel. Once Tower Bridge was open, the majority of foot traffic transferred to using the bridge, there being no toll to pay to use it. Having lost most of its income, the tunnel was closed in 1898.

Tower Bridge is one of five London bridges now owned and maintained by the Bridge House Estates, a charitable trust overseen by the City of London Corporation. It is the only one of the Trust's bridges not to connect the City of London to the Southwark bank, the northern landfall being in Tower Hamlets.
Construction started in 1887 and took eight years with five major contractors – Sir John Jackson (foundations), Baron Armstrong (hydraulics), William Webster, Sir H.H. Bartlett, and Sir William Arrol & Co. – and employed 432 construction workers. E W Crutwell was the resident engineer for the construction.

Two massive piers, containing over 70,000 tons of concrete, were sunk into the riverbed to support the construction. Over 11,000 tons of steel provided the framework for the towers and walkways. This was then clad in Cornish granite and Portland stone, both to protect the underlying steelwork and to give the bridge a pleasing appearance.

Jones died in 1887 and George D. Stevenson took over the project. Stevenson replaced Jones's original brick façade with the more ornate Victorian Gothic style, which makes the bridge a distinctive landmark, and was intended to harmonise the bridge with the nearby Tower of London. The total cost of construction was £1,184,000 (equivalent to £118 million in 2014).


Tower Bridge viewed from the top of London City Hall.

Tower Bridge viewed from The Shard.
The bridge is 800 feet (244 m) in length with two towers each 213 feet (65 m) high, built on piers. The central span of 200 feet (61 m) between the towers is split into two equal bascules or leaves, which can be raised to an angle of 86 degrees to allow river traffic to pass. The bascules, weighing over 1,000 tons each, are counterbalanced to minimise the force required and allow raising in five minutes.


The two side-spans are suspension bridges, each 270 feet (82 m) long, with the suspension rods anchored both at the abutments and through rods contained within the bridge's upper walkways. The pedestrian walkways are 143 feet (44 m) above the river at high tide.
The original raising mechanism was powered by pressurised water stored in several hydraulic accumulators.[9] The system was designed and installed by Hamilton Owen Rendel[10] while working for Sir W. G. Armstrong Mitchell & Company of Newcastle upon Tyne. Water, at a pressure of 750 psi (5.2 MPa), is pumped into the accumulators by two 360 hp (270 kW) stationary steam engines, each driving a force pump from its piston tail rod. The accumulators each comprise a 20 inches (51 cm) ram on which sits a very heavy weight to maintain the desired pressure.

The entire hydraulic system along with the gas lighting system was installed by William Sugg & Co Ltd., the well known Westminster gas engineers. The gas lighting was initially by open flame burners within the lanterns but soon after was updated to the later incandescent system.

To control the passage of river traffic through the bridge, a number of different rules and signals were employed. Daytime control was provided by red semaphore signals, mounted on small control cabins on either end of both bridge piers. At night, coloured lights were used, in either direction, on both piers: two red lights to show that the bridge was closed, and two green to show that it was open. In foggy weather, a gong was sounded as well.

Vessels passing through the bridge had to display signals too: by day, a black ball at least 2 feet (0.61 m) in diameter was to be mounted high up where it could be seen; by night, two red lights in the same position. Foggy weather required repeated blasts from the ship's steam whistle.

If a black ball was suspended from the middle of each walkway (or a red light at night) this indicated that the bridge could not be opened. These signals were repeated about 1,000 yards (910 m) downstream, at Cherry Garden Pier, where boats needing to pass through the bridge had to hoist their signals/lights and sound their horn, as appropriate, to alert the Bridge 

When needing to be raised for the passage of a vessel the bascules are only raised to an angle sufficient for the vessel to safely pass under the bridge, except in the case of a vessel with the Monarch on board in which case they are raised fully no matter the size of the vessel.

Some of the control mechanism for the signalling equipment has been preserved and may be seen working in the bridge's museum.

Reaction[edit]
Although the bridge is an undoubted landmark, professional commentators in the early 20th century were critical of its aesthetics. "It represents the vice of tawdriness and pretentiousness, and of falsification of the actual facts of the structure", wrote H. H. Statham,[14] while Frank Brangwyn stated that "A more absurd structure than the Tower Bridge was never thrown across a strategic river".

Architectural historian Dan Cruickshank selected the bridge as one of his four choices for the 2002 BBC television documentary series Britain's Best Buildings.


Tower Bridge is often[according to whom?] mistaken for London Bridge, the next bridge upstream. A popular urban legend is that in 1968, Robert McCulloch, the purchaser of the old London Bridge that was later shipped to Lake Havasu City, Arizona, believed that he was in fact buying Tower Bridge. This was denied by McCulloch himself and has been debunked by Ivan Luckin, the vendor of the bridge.

The tall ship Wylde Swan passing under Tower Bridge decorated for the London Olympics in August 2012. Note the Olympic rings folded up to allow passage of the mast.

Tower Bridge is still a busy and vital crossing of the Thames: it is crossed by over 40,000 people (motorists, cyclists and pedestrians) every day. The bridge is on the London Inner Ring Road, and is on the eastern boundary of the London congestion charge zone. (Drivers do not incur a charge by crossing the bridge.)


Tower Bridge opening at night for a ferry
To maintain the integrity of the structure, the City of London Corporation has imposed a 20 miles per hour (32 km/h) speed restriction, and an 18 tonne weight limit on vehicles using the bridge. A camera system measures the speed of traffic crossing the bridge, utilising a number plate recognition system to send fixed penalty charges to speeding drivers.


A second system monitors other vehicle parameters. Induction loops and piezoelectric sensors are used to measure the weight, the height of the chassis above ground level, and the number of axles of each vehicle.