Tower Bridge: Building an Opening Crossing for Roads and Shipping

In the latter half of the nineteenth century, population and activity increased downstream of London Bridge, making a new crossing increasingly urgent. Yet the area near the Tower of London was also a busy port, where a low fixed bridge would obstruct tall-masted vessels. In his lecture published in 1894, engineer John Wolfe Barry identified reconciliation of road traffic with trade in the upstream Pool of London as a central design problem. Tower Bridge therefore had to account for roadway gradients, ship moorings, and navigable width simultaneously.

In 1884, after comparing alternative crossings, a parliamentary committee invited the City of London to build a low-level opening bridge. Barry helped refine the bascule concept proposed by City architect Horace Jones. An initial proposal for an arch above the center was abandoned in favor of horizontal girders, preventing masts from striking the arch’s sides when vessels strayed from the center of the channel. Construction proceeded only after parliamentary authorization in 1885.

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The opening section consisted of two leaves, each rotating about a horizontal axis. As the riverward end rose, the landward counterweight descended into a space within the pier. Barry explained that this vertical movement occupied less river space than a swing bridge. The statutory clear central opening was 200 feet, about 61 meters. The side spans were carried by stiffened suspension chains, while horizontal ties above the towers connected the suspension systems on the two banks.

The towers had to accommodate stairs, lifts, and roadway machinery and could not depend solely on heavy masonry for support. A frame of steel columns, beams, and diagonal bracing was ultimately clad in granite and Portland stone to harmonize with the nearby Tower of London. The high-level walkways provided a pedestrian route while the bridge was raised and also carried the ties connecting the suspension chains on either side. Decoration, transport, and structural forces were interwoven in the same construction.

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A ceremony marking the start of work took place on June 21, 1886. Underwater foundations used wrought-iron caissons open at the top and bottom, assembled on temporary platforms and lowered under the control of screws and suspension rods. Divers excavated gravel and clay inside as the caissons sank gradually into the riverbed. Only after reaching impermeable London Clay did workers pump out the water and continue excavation and concrete placement in dry conditions. Controlling descent and level was essential to prevent the caissons from tilting.

A clear navigable width of 160 feet had to remain throughout construction, so the full platforms required for both piers could not be erected simultaneously. River traffic also impeded the mooring of construction barges, slowing foundation work beyond expectations. During subsequent installation of the high-level walkways, steel girders were cantilevered inward from both towers in stages, avoiding temporary central supports from the river. Shipping conditions shaped the construction methods, not structural calculations alone.

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The original system used steam engines to drive pumps that sent high-pressure water into accumulators fitted with heavily weighted plungers. The pumps raised the weights relatively slowly; when the bridge opened, the accumulators rapidly released pressurized water to drive the reciprocating motion of hydraulic engines. Cranks, gears, and toothed quadrants then rotated the leaves. This energy-storage method suited intermittent movements requiring high power for short periods. The steam engines did not pull the roadway directly.

Barry’s lecture also described mechanical interlocks requiring the central locking bolts, opening machinery, and signals to operate in sequence. His partner Henry Marc Brunel handled complex calculations and details; resident engineer Cruttwell managed the site; Arrol supplied the steelwork; and Armstrong, Mitchell provided the hydraulic machinery. Tower Bridge was a joint achievement of architecture, civil engineering, manufacturing, and control systems.

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The formal opening ceremony took place on June 30, 1894. City librarian Charles Welch’s history, published that year, reproduces the official program for the noon ceremony. Accompanied by the Princess of Wales and representing the Queen, the Prince of Wales first declared the bridge open to road traffic, then operated a valve lever connected to the hydraulic equipment, raised the leaves, and declared it open to river traffic. The ceremony clearly presented the rights of both forms of transport.

Welch also recorded that the 1885 act permitted borrowing £750,000, and further sums as required, against the Bridge House Estates. The construction period was later extended twice. His stated cost of more than £1.04 million was expressly qualified as not yet precisely determined and cannot be treated as a final account. Barry likewise expected construction and routine mechanical operating costs to be met from the City’s Bridge House Estates funds, with free public use.

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A formal 2004 report by Britain’s Marine Accident Investigation Branch confirms that Tower Bridge had used electrically powered oil hydraulics since 1976, continuing to open and close by hydraulic principles. The power conversion preserved the bridge’s function but could not replace operating procedures. In the May 2004 incident documented in the report, Lord Nelson struck the bridge after the master and pilot each mistakenly assumed that the other had arranged a bridge opening. In fact, no booking had been completed.

The investigation did not attribute the accident to a single failed component. It recommended advance confirmation, clear communication, decision points for aborting the passage, and contingency planning. This provides a concrete perspective on Tower Bridge’s lasting role: its opening structure turns the conflict between water and road traffic into a process that can be scheduled, but safe operation still depends on sustained cooperation among people, equipment, and port and navigation authorities.

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