Blackwall Tunnel
The Blackwall Tunnel is a pair of road tunnels underneath the River Thames in east London, linking the London Borough of Tower Hamlets with the London Borough of Greenwich, and part of the A102 road. The northern portal lies just south of the East India Dock Road ( A13) in Blackwall; A the southern entrances are just south of the The O 2 (formerly the Millennium Dome) on the Greenwich Peninsula. B Before the opening of the Dartford Tunnel in 1963, the Blackwall Tunnel was the easternmost Thames crossing for vehicles, excluding ferries. The northern approach takes traffic from the A12 and the southern approach takes traffic from the A2, making the tunnel crossing a key link for both local and longer-distance traffic between the north and south sides of the river. It forms part of a key route into Central London from South East London and Kent. The tunnels are not open to pedestrians, cyclists or other non-vehicular traffic. One bus route, the Transport for London (TfL) 108 ( Stratford- Lewisham) route, runs through the tunnels.

History
The older western tunnel was designed by Sir Alexander Binnie and built by S. Pearson & Sons, between 1892 and 1897. It was originally commissioned by the Metropolitan Board of Works but responsibility passed to the London County Council when the former body was abolished in 1889. The cost of the project was £1.4 million, and seven lives were lost during construction. The tunnel was officially opened by the Prince of Wales on 22 May 1897. The tunnel was constructed using tunnelling shield and compressed air techniques; the shield pioneer James Henry Greathead was a consultant. Sir Joseph Bazalgette, the architect of the London sewerage system, was also involved in the original planning of the project. To clear the site in Greenwich, more than 600 houses had to be demolished, including one reputedly once owned by Sir Walter Raleigh. Today the western bore is only used for northbound traffic (and is not accessible to vehicles taller than 4 m (13 ft)). The southern portal features a striking gateway built of red brick. The tunnel itself has several sharp bends, whose purpose may have been to prevent horses would not bolt once they saw daylight (motor vehicles were rare in 1897), or maybe to avoid the foundations of other structures; another theory suggests the bends avoided tunnelling through a Black Death burial ground. The tunnel carries two lanes of traffic, though higher vehicles need to keep to the left-hand lane so that they do not hit the tunnel's inner lining. The newer, eastern tunnel, opened on 2 August 1967 , is much wider, usable by vehicles up to 4.72 m (15.5 ft) and is currently used only for southbound traffic. In 1967 the lighting in the tunnel was commended as "a big improvement " on the standard provided in the "previous" tunnel. In contrast with the Victorian northbound tunnel, the eastern tunnel has no sharp bends. Its distinctive ventilation towers (right) were designed in 1961-2 by Terry Farrell, architect for the London County Council. The northern pair stand at Blackwall, while the southern are now contained within the Millennium Dome. The towers were Grade II listed in 2000.

Traffic management
The northbound Blackwall Tunnel is a traffic bottleneck with tailbacks in the morning rush hour as traffic heads north from South East London and Kent towards the London Docklands, City of London, East and Central London. To relieve the congestion, a tidal flow system was introduced in 1978, allowing northbound traffic to use the eastern tunnel. The congestion is not limited to weekday rush hours. There is often congestion with tailbacks at the weekends, especially on Sunday evenings. Due to its sharp turns with restricted headroom, high-sided vehicles can only use the left-hand lane of the western tunnel, so it was not possible to reverse the tidal flow in the evening. On 20 April 2007 the morning tidal flow was discontinued, after reports by Transport for London and the Metropolitan Police of an increase in dangerous motoring behaviour; these blamed poor driving, such as overtaking, for the decrease in safety during counterflow operations. This decision to end the counterflow was made despite a 2006 independent report, commissioned by TfL, which concluded that "the proportion of accidents occurring in and around tidal flow operations is not significantly higher than would normally be expected on this type of road" and which recommended that "accident mitigation should be focused in the first instance on speed management aspects, and specifically on the deficiencies, limitations, and in some cases, inconsistencies in the signing, signalling and road marking regime". Transport for London made the ending of the tidal flow with immediate effect without advance notice. The ending of the counterflow system has brought protests from users of the tunnel and those experiencing increased congestion due to the change. Former Mayor Ken Livingstone stated that he had "absolutely no plans to set up a congestion charging zone to charge vehicles that use the Blackwall Tunnel or the Blackwall Tunnel Approach Road. But if Greenwich wishes to do so on any of its roads then I will support them". Some unofficial commercial street maps of London show a third Blackwall Tunnel as proposed for construction, but this does not appear in the latest edition of the London A-Z: as at 2007 there were no specific plans for a third Blackwall crossing, although a 'reserved route' in an E-W direction does exist on the Greenwich Peninsula 'Master Plan'.

Maintenance and refurbishment
A major refurbishment of the Northbound tunnel is currently proposed: the levels of reactive maintenance are now considered to compromise the working of the tunnel. Fire detection systems will be installed in response to new European regulations in the light of recent tunnel fires. The Blackwall tunnel is affected by closures overnight on weekdays and over a number of whole weekends during 2010. , to the detriment of road users and local residents in North Greenwich, Poplar and beyond. The continual congestion and requirements for closures and refurbishments is unlikely to change, as the Blackwall Tunnel will remain the only major road crossing of the Thames in East London for the foreseeable future. The proposed Thames Gateway Bridge linking Thamesmead and Beckton was cancelled by Boris Johnson (Mayor of London) in 2008 stifling the regeneration of these areas of East London.

Nearest alternative crossings
The nearest alternative road crossings are the Rotherhithe Tunnel 3 mi (5 km) to the west, and the Dartford Crossing 16 mi (26 km) to the east. The Woolwich Free Ferry is 2 mi (3 km) to the east however, but is often reduced to one boat in operation, or completely closed at weekends, and cannot be relied upon as an alternative road crossing. No information is given to road users about the status of operation of the Woolwich Ferry until one reaches the approach road itself. Underground railway links include the Jubilee line from North Greenwich (TfL) to Canning Town on the east and Canary Wharf on the west. The Docklands Light Railway also passes under the Thames between Island Gardens at the southern end of the Isle of Dogs and Cutty Sark in the centre of Greenwich. Pedestrians and cyclists may also use the foot tunnels at Greenwich (close to the DLR tunnel) and Woolwich (close to the Woolwich Ferry).

Building Activity

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