Radburn was founded in 1929 as "a town for the motor age". Its planners, Clarence Stein and Henry Wright, and its landscape architect Marjorie Sewell Cautley aimed to incorporate modern planning principles, which were then being introduced into England's Garden Cities, following ideas advocated by urban planners Ebenezer Howard and Sir Patrick Geddes.

Radburn was explicitly designed to separate traffic by mode, with a pedestrian path system that does not cross any major roads at grade. Radburn introduced the largely residential "superblock" and is credited with incorporating some of the earliest cul-de-sacs in the United States

Superblocks were popular during the early and mid-20th century, arising from modernist ideas in architecture and urban planning. A superblock is much larger than a traditional city block, with greater setback for buildings, and is typically bounded by widely spaced, high-speed, arterial or circulating routes rather than by local streets. Superblocks are generally associated with suburbs, planned cities, and the urban renewal of the mid-20th century; that is, in areas in which a street hierarchy has replaced the traditional grid.
In a residential area of a suburb, the interior of the superblock is typically served by cul-de-sac roads.

Urban planner Clarence Perry argued for use of superblocks and related ideas in his "neighborhood unit" plan, which aimed to organize space in a way that is more pedestrian-friendly and provided open plazas and other space for residents to socialize. In the 1930s, superblocks were often used in urban renewal public housing projects in American cities. In using superblocks, housing projects aimed to eliminate back alleys, which were often associated with slum conditions.

Superblocks are also used when functional units such as rail yards or housing projects are too big to fit in one block.

A well-known example of a superblock is the World Trade Center site in New York City, where several streets of Manhattan's downtown grid were removed and de-mapped to make room for the center.

A supposed major advantage of the use of the superblock is to improve separation of vehicular and pedestrian circulation. New Urbanists would argue that separating those functions effectively kills the social interaction that bolsters urban areas.

The British new town of Milton Keynes is built around a grid of one-kilometer square superblocks.

referenced from wikipedia.org