Street hierarchy: Difference between revisions

Revision as of 04:30, 4 June 2018

Revision as of 01:17, 10 March 2019

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While housing unit density and, consequently, population density affects the per capita cost of infrastructure, it is not inextricably linked to the street network pattern whether hierarchical or uniform. Theoretically and historically a [[city block]] can be built at high or low density, depending on the urban context and land value; central locations command much higher land prices than suburban. The costs for street infrastructure depend largely on four variables: street width (or Right of Way), street length, block width, and pavement width. These variables affect the total street length of a neighbourhood and the proportion of land area it consumes. Street length increases costs proportionately while street area represents an opportunity cost of land unavailable for development. Studies show that regular, undifferentiated grid patterns generally incur infrastructure costs about 20 to 30 percent higher than the discontinuous hiererchical street patterns, reflecting an analogous street length increase {{citation needed|reason= Referencing "studies" and making quantitative claims without citing anything|date=January 2016}}.

In suburban areas subject to [[property tax]] caps such as California's [[California Proposition 13 (1978)|Prop 13]], the enormous per-capita expenditures required to maintain streets mean that only houses costing over half a million dollars can provide enough property tax revenue to cover the cost of maintaining their street hierarchies. In areas with low developer [[impact fee]]s, cities often fail to provide adequate maintenance of internal and arterial roads serving newly constructed subdivisions.<ref>("Fresno May End Low-Fee Policy for Developers," ''Los Angeles Times'', 23 August 2005)</ref>

Municipal records show that street maintenance represents a large portion of a municipal budget, particularly in Northern climates where snow removal is added to the regular lifecycle upkeep. Two planning strategies have been suggested to deal with these costs in new developments: reduction of street length or increase in household density, or a combination of the two. Of the two strategies, reducing street length is the most effective and permanent; densities can vary over time and cannot be effectively controlled.

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===Traffic issues===

====Congestion causes and remedies====

Most [[traffic engineering (transportation)|traffic engineers]] consider the street hierarchy to be optimal, since it eliminates through traffic on all streets except arterials. However, some have contended that it actually exacerbates [[traffic congestion]], leading to [[air pollution]] and other undesirable outcomes.<ref>https://www.theatlantic.com/issues/2000/12/budiansky.htm</ref> An alternative to street hierarchy, [[Traditional Neighborhood Development]] (TND) networks, recommended by the Institute of Traffic Engineers, implies that a type of hierarchy is desirable nonetheless. It suggests that "While TND street networks do not follow the same rigid functional classification of conventional neighborhoods with local, collector, arterial and other streets, TND streets are hierarchical to facilitate necessary movements."<ref>{{cite web |url=http://www.cues.fau.edu/cnu/docs/Traditional_Neighborhood_Development_Street_Design_Guidelines-ITE.pdf |title=Archived copy |accessdate=2017-05-23 |deadurl=yes |archiveurl=https://web.archive.org/web/20110220174833/http://www.cues.fau.edu/cnu/docs/Traditional_Neighborhood_Development_Street_Design_Guidelines-ITE.pdf |archivedate=2011-02-20 |df___location=Washington, DC}} Whashington, DC</ref>

A more precise image of the prevalent thinking about structuring road networks can be found in the 2006 ITE/CNU recommended practice for the design of urban thoroughfares.<ref>http://www.ite.org/bookstore/RP036.pdf -Context Sensitive Solutions in Designing Major Urban Thoroughfares for Walkable Communities</ref> In it, the functional, traffic-engineering classifications of roads are replaced by three basic road types: boulevard, avenue and street with the addition of a second type of boulevard – the multi-way. These road types reflect familiar names and images of roads and also real conditions in an urban environment, where each type normally performs multiple functions but only up to a limit, a hierarchical limit. For example, a boulevard can function as a principal and minor arterial but not as a collector or local access street; an avenue, as principal/minor arterial and a collector but not as a street; while a street can serve as minor arterial, a collector and a local (access road) but not as a principal arterial. These exclusions of functional roles derive from the design intention to put an emphasis either on mobility or access; both cannot be accommodated concurrently in every case.

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===Europe===

The [[Milton Keynes#Urban design|1967 design]] of [[Milton Keynes]], with its (national speed limit) grid roads at 1&nbsp;km intervals containing 'organic' road lay-out grid-squares, was strongly founded on the 'street hierarchy' principle. The 2006 [[expansion plans for Milton Keynes]] will abandon this model in favour of "mixed-use traditional British city streets".{{cncitation needed|date=June 2017}}

===Developing countries===

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

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[[Category:Road transport]]

[[Category:Transportation planning]]