Carfree Cities: City Topology

Reference Design for a six-lobe city
(click to open zoom)

1999 J.Crawford
The Design Standards for carfree cities as established in the Introduction can be achieved in a city that offers an excellent quality of life. Considerable thought has been given to the arrangement of a city which best fulfills the design standards. The resulting Reference Design described below (and on the Districts and Blocks pages) is for a city of about one million people, but the design can be adapted to cities with populations between about 300,000 and 3,000,000.

Design Attributes

The following table sums up the most important design attributes of the reference design.

	Customary Units	Metric
Population	1,000,000
Site Size	100 sq. mi.	250 sq.km
Developed Area	20% of total site
Green Area	80% of total site
Districts	99
Inhabited Districts	81
Utility Districts	18
District Population	12,000
District Diameter	2500 ft.	760 m
District Density	FAR = 1.5
Longest Journey	35 minutes
Automobile Traffic	None

The Attributes Explained

Some of the design attributes require further explanation.

100 Districts

About 100 districts would be constructed, each roughly 760 meters (2500 feet) in diameter, with streets radiating from the central transport halt. The districts are arranged in a six-leaf-clover pattern. Of the 100 districts, the 18 districts farthest from the city center are "utility areas." These non-residential areas are reserved for various infrastructure requirements, heavy industry, and parking.

Six Lobes

One of the six lobes

1999 J.Crawford

The districts are arranged into six lobes. This arrangement has several advantages:

There are only three metro routes, each beginning in one lobe, running into the center, and back out to an adjacent lobe.
The three routes do not cross one another but each can be brought adjacent to all the others for transfers. More than three routes cannot usefully be arranged in such a pattern.
The walking distances at the transfer points are kept short, there are three transfer locations instead of one large, crowded central location, and only one transfer is ever required.
Each district is surrounded by at least a narrow greenbelt.
The efficiency of the transport system is high, construction costs are minimized, and journey times are kept short.
All areas of the city are within quick reach of the center.

20% Urbanized

In order to provide plenty of open space, only 20% of the area of the full site would be developed. Green space would comprise the remaining 80% of the site. However, in cases where land is at a premium, it is possible to increase the density to the point where the districts all touch, leaving only small green areas between.

35 Minutes to Anywhere

The worst-case transit time between any two points in the city is about 35 minutes. This arises when the origin of the trip is at the outside edge of one of the utility areas and the destination is also at the outside edge of a utility area located on a different metro line.

Adjustments for Size

The number of districts could be easily adjusted to suit the desired size of the city. Fewer than about 50 districts indicates either that the topology could be simplified or that the density could be reduced. More than about 200 districts begins to lengthen the transit time excessively, yielding worst-case transit times approaching 50 minutes. This provides room for about 2,000,000 inhabitants.

Up to around 3,000,000 people, the length of the lobes could be increased still farther, but maximum transit times rise to about one hour, which I regard as the extreme limit of acceptability.

Above this, some other form is required. I would prefer to build several sister cities, each with a million inhabitants, arranged in a rough circle, with the centers of these cities linked by high speed rail. With such an arrangement, worst-case transit time between any two points in the metropolitan area is about 45 minutes. This would accommodate cities up to around 6,000,000.

If each of the sister cities is allowed to grow to 2,000,000 inhabitants, then a city of 12,000,000 is possible, with maximum journey times of a little over an hour. Topologies supporting even larger populations can be imagined.

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