Tokyo (1960) / City as a Tree and Transportation as Branches
“The structural element is thought of as a tree – a permanent element,
with dwelling units as leaves – temporary elements which fall down
and are renewed according to the needs of the moment.
The buildings can grow within this structure and die and grow again – but the structure remains.”
— Kenzo Tange 
The tree represents not only a specific hierarchical organizational structure, through its possession of a trunk, roots, branches, and leaves but can also be read as a symbolic figure referring to life and growth that the branches and roots can extend while the leave could fall apart and regenerate. This entry would focus on how and why the automobile system were designed based on Kenzo Tange envision in this metaphor on transportation system in Tange’s Tokyo plan.
The structural hierarchy was originated from the difference between mass transportation, automobile and pedestrian flow with special highlight on the “door to door mobility” of automobile which lie between the other distinct two. Even though buildings open on a street, it is usually impossible to park cars right in front of it and it would block pedestrian circulation. There is a need for a new sequence in which the automobile moves from high-speed highways to low-speed highways and then to parking spaces from which passengers in the automobile can approach buildings. 
This revealed in the design of the civic axis as the trunk which is detached from the ground that the root (pedestrian walkway) and the branch (the road for automobile) is separated. There are three levels of cyclical system for the civic axis would be divided in accordance with the speed of vehicles moving along them with the highest the fastest, and the lowest level would be a unit of a man made “ground” which would contain several levels of parking space.
To connected the urban transportation system with the architectural system, Tange was inspired by Le Corbusier’s pilotis area which act as a transition space between transportation and private live-work space. He further develops this area and divide it to two levels, the upper one for pedestrian and the lower one for automobiles and parking.
By then, people would enter the parking space in their cars, get out of the vehicles, and then ride up into buildings in elevators situated in vertical cores. In this way the unit urban area and the highway system would inter mesh, and there would be spatial order as well as a speed hierarchy linking, first, streets, interchanges, parking spaces, and buildings, and second, high speed, low speed, human speed, and immobility. 
Regarding the regenerative feature in the hierarchy, Tange noted the different in metabolic rate of the branches and leaves that large-scale transportation system are regard as “fixed” while the residential blocks and articles of daily life would be “transient” that shows more identity and under rapid changes along time. With improved technologies and the “throw away” consumerism trend, it is predicted that the “fixed” part would stay longer and the “transient” part would have a shorter lifespan.
The “fixed” part could be construct in a “loop” unit by unit which is composed of a series of unending links, each link of which serves as a steady cycle of flow and any number of links could be employed. The grid on which the street system is based on consists of squares with side length of one kilometer allowed for further expansion where the system would keep the same.
Whereas the “transient” part would be the architectural blocks with core system, in which the vertical traffic in buildings as well as the service arteries – water ducts and electric wiring -are gathered together in single shafts forming the nuclei of buildings. The cores of buildings would become branches of the urban transportation and service arteries, but allow rapid modification and maintenance work.
 Banham, Reynor. Megastructure. New York, U.S.A.: Harper and Row, 1976
 Kenzo Tange Team. “A PLAN FOR TOKYO, 1960.” Ekistics 12, no. 69 (1961): 9-19. http://www.jstor.org/stable/43613534.
 Lin, Zhongjie. Kenzo Tange and the Metabolist Movement: Urban Utopias of Modern Japan. New York: Routledge, 2010.