For a very thorough and extremely well illustrated explanation of the advantages of narrow streets, please see these definitive posts by A.A. Price: Human-Scale Streets and Narrow Streets.

A.A. Price’s posts demonstrate viscerally the aesthetic value of narrow streets.  But how can we quantify this quality?

First, we must look at what we mean by street width; does it refer to the width of the road itself, or the distance between the two building facades that frame the street?

Both definitions have value, but let’s clarify our definitions first:

• Road: the vehicular right of way; where cars have de-facto precedence over pedestrians.  Chuck Marohn gives an explanation of roads here.
• Street: the whole area between the two rows of buildings fronting the street (lawns, sidewalk, road, etc).

Both definitions are simple enough, but they only apply to a single street.  To provide a wholistic picture of a neighborhood’s street structure, the Narrow Streets Index must be richer than a single number; it becomes a Narrow Streets Distribution Curve.

Example 1 – Shimokyo-machi in Sasebo, Japan (佐世保 下京町)

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To simplify the analysis, we will ignore the streets which form the edges of the neighborhood (thus emphasizing the neighborhood’s internal continuity, and ignoring its connectivity to other areas):

• Magenta = boundary of Shimokyo-machi (encompassing 8 blocks and 440,000 sq ft)
• Red = streets (drawn from facade to facade)
• Green = covered pedestrian arcade

Street width :: Total length of street having this width

• 　＞１００’ :: ３５０’
• 　　　５０’ :: ２３０’    (the triangular open area.)
• 　　　３６’ :: ４８０’    (the Shimokyo portion of covered arcade)
• ２７’-３３’ :: ７４０’
• 　　　１５’ :: ９１０’

 

Example 2 – The north-west corner of Whittier, in Minneapolis, Minnesota

• Magenta = boundary of neighborhood (encompassing 6 blocks and 1.3 million sq ft)
• Red = streets (drawn from facade to facade)

Street width :: Total length of street having this width

• 　＞１００’ :: １４７０’
• ８８ー９１’ :: １１８０’
• 　　　８１’ :: 　５９０’

Comparing the two neighborhoods on a single chart:

• Blue = Shimokyo-machi, Sasebo (the spike at 105′ is a national freeway, and the widest road in Sasebo)
• Red = Minneapolis (NW corner of Whittier, near the “Wedge” neighborhood)

As can be seen here, the street widths (building to building) are much narrower in Sasebo.

It may also be observed that the street width distribution in Minneapolis is tightly bunched around the 80-105′ range, and misses out completely on anything that could be called a “narrow street” (indicating a low level of fractal complexity?　#自己相似).

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Here is the comparison of road widths:

Why does Shimokyo-machi have so little road?  Because two of its streets are pedestrian only: the covered arcade, and the 15′ wide street on the NE side of the freeway (the road portion of those streets are shown in the graph as having zero width).

Road width :: Total length of road having this width (Shimokyo-machi)

• 　　　９５’ :: ３５０’    (the national freeway)
• 　　　３６’ :: ４８０’    (the pedestrian arcade; road portion counted as ０’ wide)
• 　　　２７’ :: ３７０’    (actually, this street appears to function as a woonerf)
• 　　　２２’ :: ３７０’    (the speed limit is under 19 mph, but this is probably the least pedestrian-friendly street in Shimokyo-machi).
• 　　　１５’ :: ６２０’    (actually, both these streets are de facto woonerfs)
• 　　　１３’ :: １６０’    (the cargo lane on the side of the triangular open space)

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Here is a comparison with Hoboken, New Jersey, with street widths on the vertical axis, and total length on the horizontal axis:

We can see that the street widths of Hoboken are generally much narrower than in Minneapolis, and generally much wider than in Sasebo.  Hoboken has a wide range of street widths (from 20′ to 110′), but only the larger streets (62′-110′) follow an organic (fractal) distribution; the total length of narrower streets is too small.

Only “enclosed” streets were measured for the Hoboken analysis (streets with buildings on both sides):

• The long “alley” (in green) is Court Street.  It is only 20 feet wide, but it does function as a regular street (see slideshow below).
• The three short streets at the top (in green) are car-free zones.

Court Street:

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The car-free zones at the north end of Hoboken:

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