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The A102 starts in Clapton in the north London Borough of Hackney and ends at the Sun-in-the-Sands interchange in Kidbrooke in the south Royal Borough of Greenwich, where it continues as the A2 towards the south coast.

The A102 was formerly a continuous route including two motorway sections classified as the A102(M) however, subsequent to the renumbering of part of the route in 1999, the A102 designation belongs only to the section including the Blackwall Tunnel linking the A12 and the A2 and also to the section from Clapton to Hackney Wick.

The A102(M) section of the road lost its motorway status following the formation of the Greater London Authority (GLA) and the subsequent transfer of all trunk roads except M1, M4 and M11 to Transport for London (Link SABRE Wiki).

The Blackwall Tunnels are a pair of Tunnels on the A102 under the River Thames, linking the London Borough of Tower Hamlets on the north side with the Royal Borough of Greenwich on the south. The northern portal lies just south of the East India Dock Road (A13) in Blackwall; the southern entrances are just south of The O2 Arena on the Greenwich Peninsula. The road is managed by Transport for London (TfL).

The first tunnel was originally opened as a single bore in 1897 as a major transport project to improve commerce and trade in London's East End in an age before motor vehicles. As such it is designed for horse drawn traffic and includes a number of tight bends, reputedly to prevent horses seeing daylight in the distance. By the 1960s, traffic levels had reached the point where a second tunnel was required; this was built to the east of the original tunnel and to a more modern alignment. The new tunnel opened in 1967 and now carries southbound traffic, leaving the original tunnel to carry northbound traffic.

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 and is the easternmost free fixed road crossing of the Thames, and regularly suffers congestion.

The tunnels are no longer open to pedestrians, cyclists or other non-motorised traffic, and the northbound tunnel has a 4.0-metre height limit. One bus route runs through the tunnels.