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7.1. Small Blocks

Aus Pattern Language Wiki

(Weitergeleitet von Small Blocks)

Within the network of Walkable Multi-Mobility, there is a scale of block patterns that is most conducive to walking.


07 1 01 Small Blocks.jpg


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Problem-statement: Blocks that are too big create street networks that are unwalkable. But there is a practical limit to how small a block can be.


Discussion: Blocks that are smaller than about 60 meters in any one direction (about 200 feet), exclusive of the street right of way, create problems for accommodating outdoor space or alley conditions within the blocks. A more optimal minimum dimension is about 70 meters (230 feet).


But blocks that get much larger than double this distance in their longest dimension — about 150 meters or 500 feet — begin to create long pathways for pedestrians that discourage walking.


Jane Jacobs, in her landmark The Death and Life of Great American Cities, argued that small blocks are one of the four most important factors in generating diversity, in turn the most essential ingredient of great cities. She noted that long blocks disrupt the “intricate pools of fluid street use” that are necessary to support diverse economic and cultural interactions, and to maintain a “fabric of intimate economic cross-use”. In addition, shorter blocks help to generate more visual interest and more attractive walking experiences. Jacobs suggested that a block size much greater than about 400 feet (about 120 meters) was problematic.


Recent research has tended to confirm these insights, but added some nuance to the picture. One of the complicating factors is that block size need not be the same in length and width, and indeed may be irregular. Where one dimension is shorter, another dimension may be longer, and still result in an overall walkable form.¹


Smaller block size is also correlated with a denser street pattern, which has also been shown to be beneficial for walking and multi-modal transportation as well as active living and health outcomes.²


Yet another factor is the overall pattern of street connectivity, in which smaller block size plays an important role in promoting greater connectivity. Hillier and his associates have developed a “space syntax” model for street design, in which it can be shown that “natural” pedestrian movements (including those to commercial destinations) are dependent on “global properties of the street grid”. This is a confirmation of Jacobs’ insight that block sizes affect economic patterns and interactions.³


Unfortunately, today many commercial forces push towards gigantism, with the result that blocks of correct size have been amalgamated into large superblocks in many parts of the world, with their essential fine grain of streets removed. The result turns out to be negative for the users, and for the city as a whole (and perhaps positive only for the real estate speculators). For as we have seen, such an out-scale disruption strains and often damages the urban fabric, not only on the site and in the immediate vicinity, but also throughout the surrounding area. Jacobs memorably referred to the destructive edges of these superblocks as “border vacuums.”


07 1 02 Small Blocks.jpg
The small blocks of Portland, Oregon — almost too small perhaps, but praised by Jane Jacobs and others for their walkability.


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Therefore:

Lay out blocks so that their shortest dimensions are roughly 70 meters (230 feet) and no more than 90 meters or approximately 300 feet. Make their longest dimensions no more than about 150 meters or 500 feet.


07 1 03 Small Blocks.jpg


Create a mix of block sizes using Small Plots within regulated parameters. Use the Perimeter Building pattern at the edges of the blocks. …




¹ The correlation of smaller block size with walkability was later demonstrated by a number of researchers. See for example Moudon, A. V., Lee, C., Cheadle, A. D., Garvin, C., Johnson, D., Schmid, T. L., & Lin, L. (2006). Operational definitions of walkable neighborhood: theoretical and empirical insights. Journal of Physical Activity and Health, 3(s1), S99-S117. Additional nuance came from a study by Sevstuk and colleagues, suggesting that there are tradeoffs from smaller blocks, and that it is possible to be too small — see Sevstuk, A., Kalvo, R., & Ekmekci, O. (2016). Pedestrian accessibility in grid layouts: The role of block, plot and street dimensions. Urban Morphology, 20(2), 89-106.


² See for example Marshall, W. E. & Garrick, N. W. (2010). Effect of street network design on walking and biking. Transportation Research Record, 2198(1), 103-115. The same authors looked at data for traffic safety and also found a benefit: Marshall, W. E., & Garrick, N. W. (2011). Does street network design affect traffic safety?. Accident Analysis & Prevention, 43(3), 769-781.


³ See Hillier, B., Penn, A., Hanson, J. Grajewski, T., & Xu, J. (1993). Natural movement: or, configuration and attraction in urban pedestrian movement. Environment and Planning B: Planning and Design, 20(1), 29-66.



SECTION I:

PATTERNS OF SCALE


1. REGIONAL PATTERNS

Define the large-scale spatial organization…

1.1. POLYCENTRIC REGION

1.2. BLUE-GREEN NETWORK

1.3. MOBILITY CORRIDOR

1.4. 400M THROUGH STREET NETWORK

2. URBAN PATTERNS

Establish essential urban characteristics…

2.1. WALKABLE MULTI-MOBILITY

2.2. LEVEL CITY

2.3. PUBLIC SPACE SYSTEM

2.4. BIOPHILIC URBANISM

3. STREET PATTERNS

Identify and allocate street types…

3.1.URBAN GREENWAY

3.2. MULTI-WAY BOULEVARD

3.3. AVENUE

3.4. SHARED SPACE LANE

4. NEIGHBORHOOD PATTERNS

Define neighborhood-scale elements…

4.1. STREET AS CENTER

4.2. PEDESTRIAN SANCTUARY

4.3. NEIGHBORHOOD SQUARE

4.4. NEIGHBORHOOD PARK

5. SPECIAL USE PATTERNS

Integrate unique urban elements with care…

5.1. SCHOOL CAMPUS

5.2. MARKET CENTER

5.3. INDUSTRIAL AREA

5.4. HOSPITAL

6. PUBLIC SPACE PATTERNS

Establish the character of the crucial public realm…

6.1. PLACE NETWORK

6.2. WALKABLE STREETSCAPE

6.3. MOVABLE SEATING

6.4. CAPILLARY PATHWAY

7. BLOCK AND PLOT PATTERNS

Lay out the detailed structure of property lines…

7.1. SMALL BLOCKS

7.2. PERIMETER BLOCK

7.3. SMALL PLOTS

7.4. MID-BLOCK ALLEY

8. STREETSCAPE PATTERNS

Configure the street as a welcoming place…

8.1. STREET AS ROOM

8.2. TERMINATED VISTA

8.3. STREET TREES

8.4. STREET FURNISHINGS

9. BUILDING PATTERNS

Lay out appropriate urban buildings…

9.1. PERIMETER BUILDING

9.2. ARCADE BUILDING

9.3. COURTYARD BUILDING

9.4. ROW BUILDING

10. BUILDING EDGE PATTERNS

Create interior and exterior connectivity…

10.1. INDOOR-OUTDOOR AMBIGUITY

10.2. CIRCULATION NETWORK

10.3. LAYERED ZONES

10.4. PASSAGEWAY VIEW



SECTION II:

PATTERNS OF MULTIPLE SCALE


11. GEOMETRIC PATTERNS

Build in coherent geometries at all scales…

11.1. LOCAL SYMMETRY

11.2. SMALL GROUPS OF ELEMENTS

11.3. FRACTAL PATTERN

11.4. FRAMING

12. AFFORDANCE PATTERNS

Build in user capacity to shape the environment…

12.1. HANDLES

12.2. CO-PRODUCTION

12.3. FRIENDLY SURFACES

12.4. MALLEABILITY

13. RETROFIT PATTERNS

Revitalize and improve existing urban assets …

13.1. SLUM UPGRADE

13.2. SPRAWL RETROFIT

13.3. URBAN REGENERATION

13.4. URBAN CONSOLIDATION

14. INFORMAL GROWTH PATTERNS

Accommodate “bottom-up” urban growth…

14.1. LAND TENURE

14.2. UTILITIES FIRST

14.3. DATA WITH THE PEOPLE

14.4. INCREMENTAL SELF-BUILD

15. CONSTRUCTION PATTERNS

Use the building process to enrich the result…

15.1. DESIGN-BUILD ADAPTATION

15.2. HUMAN-SCALE DETAIL

15.3. CONSTRUCTION ORNAMENT

15.4. COMPLEX MATERIALS



SECTION III:

PATTERNS OF PROCESS


16. IMPLEMENTATION TOOL PATTERNS

Use tools to achieve successful results…

16.1. FORM-BASED CODE

16.2. ENTITLEMENT STREAMLINING

16.3. NEIGHBORHOOD PLANNING CENTER

16.4. COMMUNITY MOCKUP

17. PROJECT ECONOMICS PATTERNS

Create flows of money that support urban quality…

17.1. TAX-INCREMENT FINANCING

17.2. LAND VALUE CAPTURE

17.3. EXTERNALITY VALUATION

17.4. ECONOMIES OF PLACE AND DIFFERENTIATION

18. PLACE GOVERNANCE PATTERNS

Processes for making and managing places…

18.1. SUBSIDIARITY

18.2. POLYCENTRIC GOVERNANCE

18.3. PUBLIC-PRIVATE PLACE MANAGEMENT

18.4. INFORMAL STEWARDSHIP

19. AFFORDABILITY PATTERNS

Build in affordability for all incomes…

19.1. INTEGRATED AFFORDABILITY

19.2. COMMUNITY LAND TRUST

19.3. MULTI-FAMILY INFILL

19.4. SPECULATION TAX

20. NEW TECHNOLOGY PATTERNS

Integrate new systems without damaging old ones…

20.1. SMART AV SYSTEM

20.2. RESPONSIVE TRANSPORTATION NETWORK COMPANY

20.3. AUGMENTED REALITY DESIGN

20.4. CITIZEN DATA