The Blackwall Tunnel is a pair of road tunnel

Tunnel

A tunnel is an underground passageway, completely enclosed except for openings for egress, commonly at each end.A tunnel may be for foot or vehicular road traffic, for rail traffic, or for a canal. Some tunnels are aqueducts to supply water for consumption or for hydroelectric stations or are sewers...

s underneath the River Thames

River Thames

The River Thames flows through southern England. It is the longest river entirely in England and the second longest in the United Kingdom. While it is best known because its lower reaches flow through central London, the river flows alongside several other towns and cities, including Oxford,...

 in east London

London

London is the capital city of :England and the :United Kingdom, the largest metropolitan area in the United Kingdom, and the largest urban zone in the European Union by most measures. Located on the River Thames, London has been a major settlement for two millennia, its history going back to its...

, linking the London Borough of Tower Hamlets

London Borough of Tower Hamlets

The London Borough of Tower Hamlets is a London borough to the east of the City of London and north of the River Thames. It is in the eastern part of London and covers much of the traditional East End. It also includes much of the redeveloped Docklands region of London, including West India Docks...

 with the London Borough of Greenwich

London Borough of Greenwich

The London Borough of Greenwich is an Inner London borough in south-east London, England. Taking its name from the historic town of Greenwich, the present borough was formed in 1965 by the amalgamation of the former area of the Metropolitan Borough of Greenwich with part of the Metropolitan...

, and part of the A102 road

A102 road

The A102 is a road that starts in Clapton in the north London Borough of Hackney and ends in Kidbrooke in the south London Borough of Greenwich. The A102 was formerly a continuous route including two motorway sections classified as the A102 however, subsequent to the renumbering of part of the...

. The northern portal lies just south of the East India Dock Road (A13) in Blackwall

Blackwall, London

Blackwall is an area of the East End of London, situated in the London Borough of Tower Hamlets on the north bank of the River Thames.The district around Blackwall Stairs was known as Blackwall by at least the 14th century. This presumably derives from the colour of the river wall, constructed in...

; the southern entrances are just south of The O₂

The O2 (London)

The O2, visually typeset in branding as The O2, is a large entertainment district on the Greenwich peninsula in South East London, England, including an indoor arena, a music club, a Cineworld cinema, an exhibition space, piazzas, bars and restaurants...

 (formerly the Millennium Dome

Millennium Dome

The Millennium Dome, colloquially referred to simply as The Dome or even The O2 Arena, is the original name of a large dome-shaped building, originally used to house the Millennium Experience, a major exhibition celebrating the beginning of the third millennium...

) on the Greenwich Peninsula

Greenwich Peninsula

Greenwich Peninsula is an area of South London, England, located in the London Borough of Greenwich.The peninsula is bounded on three sides by a loop of the Thames, between the Isle of Dogs and Silvertown. To the south is the rest of Greenwich, to the south-east is Charlton.The peninsula lies...

. Before the opening of the Dartford Tunnel

Dartford Crossing

The Dartford - Thurrock River Crossing, Dartford River Crossing is a major road crossing of the River Thames in England, connecting Dartford in the south to Thurrock in the north, via two road tunnels and the Queen Elizabeth II Bridge. It opened in stages, the west tunnel in 1963, the east 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

A2 road (Great Britain)

The A2 is a major road in southern England, connecting London with the English Channel port of Dover in Kent. This route has always been of importance as a connection between the British capital of London and sea trade routes to Continental Europe...

, making the tunnel crossing a key link for both local and longer-distance traffic between the north and south sides of the river.