Condition 2: Short Blocks – Creating an Index

“Most blocks must be short; that is, streets and opportunities to turn corners must be frequent.”

-The Death and Life of Great American Cities; Chapter 9, “The need for small blocks”.

It’s a little bit tricky to define precisely what it means for a block to be short.  It appears that Jacobs’s intended metric is not so much the actual size of blocks, as the frequency of street intersections, and the number of sensible routes between various points A and B.

Creating an Index

Measuring the number of sensible routes between various points is a time-consuming task.  For now let us focus solely on the frequency of street intersections, and use that as our metric for satisfying Jane Jacobs’s Condition 2.

Here I compare 4 cityscapes at the same scale, and thus each map has the same area.

Let us give a weighted value to each intersection, depending on how many streets intersect there:  value = number of streets – 2.  Then a three-way or “T” intersection will have a value of 1, and a four-way intersection will have a value of 2.  This way, ambiguity about whether streets meet at a single 4-way or adjacent 3-way intersections won’t affect the result.

 

Berkeley - Durant & Fulton Area - 50 ft g-scale
Berkeley – Durant & Fulton Area – 50 ft g-scale

Berkeley

Short Block Index: 5  (2 four-way, 1 three-way)

 

Kobe - City Tower Area - 50 ft g-scale
Kobe – City Tower Area – 50 ft g-scale

Central Kobe, near City Tower

Short Block Index: 13  (5 four-way, 3 three-way)

 

Kobe - Kitano Area - 50 ft g-scale
Kobe – Kitano Area – 50 ft g-scale

Kobe, Kitano-Cho

Short Block Index: 18  (1 five-way, 1 four-way, 13 three-way)

 

Mpls - Espresso Royale Area - 50 ft g-scale
Mpls – Espresso Royale Area – 50 ft g-scale

Downtown Minneapolis

Short Block Index: 9  (4 four-way, 1 three-way)

 

Summary of Results

Area :: Short Block Index

Kobe, Kitano-Cho :: 18

Kobe, City Tower area :: 13

Minneapolis, downtown :: 9

Berkeley :: 5

 

 

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2 thoughts on “Condition 2: Short Blocks – Creating an Index

  1. “So even compared to Portland, Tokyo’s blocks are much smaller, as little as one quarter of Portland’s blocks. The streets are extremely narrow in those blocks, as little as 4 meters across (around 13 feet). In such a context, car speed is significantly reduced by the narrowness of roadways, the presence of pedestrians and cyclists and the number of intersections, making walking and biking much more attractive in comparison.”

    http://urbankchoze.blogspot.com/2014/06/sapporo-relevant-japanese-model-for.html

    [also has some great diagrams of Manhattan and Portland street grids super-imposed on Tokyo and Sapporo]

    Like

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