Street hierarchy: Difference between revisions

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{{Short description|Urban planning restricting through traffic of automobiles}}

{{Multiple issues|

{{Original research|date=October 2023|reason=Several paragraphs contain unsourced information on a niche subject.}}

{{more citations needed|date=July 2019}}

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[[File:Radburn Cellular Street Pattern.jpg|thumb|300px|right|The network structure of [[Radburn, New Jersey]] exemplifies the concept of street hierarchy of contemporary districts. (The shaded area was not built.)]]

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In the pre-automotive era of cities, traces of the concept of a hierarchy of streets in a network appear in Greek and subsequent Roman town plans. The main feature of their classification is their size. In Roman cities, such as [[Pompeii]], major thoroughfares (e.g. the [[Decumanus Maximus|decumanus]]) had a width of 12.2 m, secondary streets (e.g. the [[cardo]]) 6 m and tertiary streets (e.g. vicinae) measured 4.5 meters. The first allowed for two way cart traffic, the second generally only one, while the third only loaded animals. Narrower streets that could only accommodate pedestrians were also present in both Greek and Roman cities. Thus the restriction on connections between major streets on particular modes (carts and chariots) was the effect of the width of the street itself and not the lack of linkage. This method is akin to the contemporary concept of [[permeability (spatial and transport planning)|filtered permeability]].

A clearer record of a stricter hierarchical order of streets appears in surviving and functioning Arabic-Islamic cities that originate in the late first millennium AD such as the [[Medina of Tunis]], [[Marrakesh]], [[Fes el Bali|Fez]], and [[Damascus]]. In theseThese cases there arefeature four classes of streets starting with the cul-de-sac type (1.84-2.00 m wide) and moving up to the local (third order connector), then a collector that usually surrounds a residential quarter (second order connector) and, finally, to the first order connector (arterial). The latter connector usually crossed the city through its centre and led to the city gates (see drawing). These arterials were decreed to be at least wide enough for two crossing loaded animals, 3.23 to 3.5 m.<ref>Besim Hakim 1986, Arabic-Islamic Cities – Building and Planning Principles KPI Ltd, London</ref> This tendency for hierarchical organization of streets was so pervasive in the Arab-Islamic tradition that even cities that were laid out on a uniform grid by Greeks or Romans, were transformed by their subsequent Islamic conquerors and residents, as in the case of Damascus.<ref>Nezar Alsayyad, 1991 Cities and Caliphs: on the Genesis of Arab Muslim Urbanism, Greenwood Press</ref>

In the automotive 20th century, the street hierarchy concept was first elaborated by [[Ludwig Hilberseimer]], in his ''City Plan'' of 1927. His major priorities were increasing the safety of [[primary school]]-age children [[walk to school campaign|walking to school]], and increasing the speed of traffic.

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====Safety====

Transportation planners and traffic engineers have expressed concerns over the traffic safety drawbacks presented by the street hierarchy. Recent studies have found higher traffic fatality rates in outlying suburban areas than in central cities and inner suburbs with smaller blocks and more-connected street patterns.<ref>http://www.minority.unc.edu:9014/sph/minconf/2004/materials/ewing.etal.pdf

{{deadlinkdead link|date=November 2020}}</ref><ref>{{cite web |url=http://www.virginia.edu/topnews/releases2002/lucy-april-30-2002.html |title=Archived copy |access-date=2006-09-03 |url-status=dead |archive-url=https://web.archive.org/web/20060903234004/http://www.virginia.edu/topnews/releases2002/lucy-april-30-2002.html |archive-date=2006-09-03 }}</ref> While some of this disparity is the result of distance from emergency medical facilities (hospitals are usually not built in a newly developed suburban area until a fairly late stage in its development), it is clear that the higher speeds engendered by the street hierarchy increase the severity of accidents occurring along arterial roads.

An earlier study<ref>Eran Ben-Joseph, Livability and Safety of Suburban Street Patterns: A Comparative Study (Berkeley, CA: Institute of Urban and Regional Development, University of California, Working Paper 641, 1995)</ref> found significant differences in recorded accidents between residential neighbourhoods that were laid out on an undifferentiated grid and those that included culs-de-sac and crescents in a hierarchical structure. The frequency of accidents was significantly higher in the grid neighbourhoods.

Two newer studies examined the frequency of collisions in two regional districts using the latest analytical tools. They investigated the potential correlation between street network patterns and frequency of collisions. In one study,<ref>Using Macrolevel Collision Prediction Models in Road SafetyPlanning Applications Gordon R. Lovegrove and Tarek Sayed Transportation Research Record: Journal of the Transportation Research Board, No. 1950, Transportation Research Board of the National Academies, Washington, D.C., 2006, pp. 73–82</ref> cul-de-sac hierarchical networks appeared to be much safer than the uniform grid networks, by nearly three to one.

A second study<ref>Sun, J. & Lovegrove, G. (2009). Research Study on Evaluating the Level of Safety of the Fused Grid Road Pattern, External Research Project for CMHC, Ottawa, Ontario</ref> found the grid plan to be the least safe by a significant margin with respect to all other street patterns.

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===Banning on-street parking===

Banning on-street parking can provide social benefits if the car users and the general public pay for off-street parking.<ref>[https://trid.trb.org/view/1567244] Transportation Research Board | On-street versus off-street parking: an urban economic analysis | Created: Nov 12 2018</ref><ref>[https://web.archive.org/web/20220105160458/https://safety.fhwa.dot.gov/saferjourney1/library/countermeasures/55.htm] Federal Highway Administration |On-Street Parking</ref><ref>[https://escholarship.org/content/qt3xj0q23z/qt3xj0q23z_noSplash_946f2e7b912e7cc9e71f98c81b3912d0.pdf] Shoup, Donald. "On-Street parking management v. Off-Street parking requirements." The access almanac 42 (2013): 38-40.</ref>

==Future prospects==

{{refimprovemore citations needed|section|date=November 2020}}

===United States===

While street hierarchies remain the default mode of suburban design in the United States, its 21st century usefulness depends on the prevalence of low density developments. To the degree that developable land becomes scarce in coastal urban areas and in geographically constrained inland cities such as [[Tucson, Arizona|Tucson]], [[Las Vegas, Nevada|Las Vegas]], and [[Salt Lake City, Utah|Salt Lake City]], the street hierarchy's inability to handle any but the lowest population densities is a long-term liability. The street hierarchy is also unpopular in the coastal city of [[New Orleans, Louisiana|New Orleans]] because of its geographic barriers, and because like Philadelphia, New York, and Cleveland, New Orleans already had suburbs before the new design became popular. Grids were used in New Orleans to fit a population that had at one time reached over 700,000 into {{convert|180|sqmi|km2}} of land with over 20 percent of that number being dedicated to uninhabitable wetlands. There a street hierarchy took up too much space to be economical. Real estate developers in areas with high land prices, such as Southern California's [[Inland Empire]], are finding that the relatively high population density of contemporary subdivisions is leading to severe traffic congestion on arterial roads that were country lanes a decade earlier. The street hierarchy is also becoming less attractive as awareness increases of the environmental consequences of the urban planning paradigm of which it is an integral part. The "[[smart growth]]" movement calls for street patterns with a high degree of connectivity, and with it a more balanced provision for various travel modes, both vehicular and non-vehicular.

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*{{Annotated link|Pedestrian zone}}

*{{Annotated link|Permeability (spatial and transport planning)}}

*[[Radial route]]

*[[Ring road]]

*[[Settlement hierarchy]]

*[[Side road]]

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*Kunstler, James Howard (1993). ''The Geography of Nowhere: The Rise and Decline of America's Man-Made Landscape''. New York: Simon and Schuster. {{ISBN|0-671-70774-4}}.

*Nivola, Pietro (1999). ''Laws of the Landscape: How Policies Shape Cities in Europe and America''. Washington: Brookings Institution Press. {{ISBN|0-8157-6081-7}}.

*Southworth Michael and Eran Ben-Joseph (2003). ''Streets and the Shaping of Towns and Cities.'' {{ISBN|9-781559-639163}}

{{Road types}}

[[Category:Hierarchy]]

[[Category:Road transport]]