Fused grid
The fused grid is a street network pattern first proposed in 2002 and subsequently applied in Calgary, Alberta and Stratford, Ontario. It represents a synthesis of two well known and extensively used network concepts: the "grid" and the "Radburn" pattern, derivatives of which are found in most city suburbs. Both concepts were conscious attempts to organize urban space for habitation. The grid was conceived and applied in the pre-automotive era of cities starting circa 2000 BC and prevailed until about 1900 AD. The Radburn pattern emerged in 1929 about thirty years following the invention of the internal combustion engine powered automobile and in anticipation of its eventual dominance as a means for mobility and transport. Both these patterns appear throughout North America. "Fused" refers to a systematic recombination of the essential characteristics of each of these two network patterns.
Terminology and history
Modern urban planners generally classify street networks as either organic or planned. Planned networks tend to be organized according to geometric patterns, while the organic networks are believed to emerge from spontaneous, unorganized growth.Architectural historian Spiro Kostof writes that "The word 'grid' is a convenient, and imprecise, substitute for 'orthogonal planning'. 'Gridiron' in the US implies a pattern of long narrow blocks, and 'checkerboard' a pattern of square blocks." In addition to the right angle being a key characteristic, a second attribute of equal importance is its imputed openness and unconstrained expandability. Loosely interpreted, the term "grid" can be applied to plans such as the Vitruvian octagonal plan for an ideal city, resembling a spider web, or to plans composed of concentric circles. These are all grids in that a regularly spaced armature leaves recurring openings and that they could, conceivably, expand outward.
The emergence of the pure, rectilinear, orthogonal grid, or Hippodamian grid, is explained by the natural tendency of people to walk in a straight line, particularly in the absence of obstacles and on level land. This intuitive explanation leaves the question of pre-grid and post grid non-rectilinear city patterns to be better understood, particularly those on plane territory such as Marrakech. Another potential influence may have been exerted by the second frequent user of city streets – horses. Horses also tend to move in a straight line, particularly at trotting, canter or galloping pace. When horses serve a city and draw chariots singly or in pairs, or, similarly, carts for a variety of transportation and processional functions, straight line travel becomes imperative; turns force a sluggish pace and cumbersome manoeuvres that reduce their efficiency of movement. The need for speed is accentuated by city size; distances to the public functions at the centre increase and, consequently, the need for quick access is intensified. Speed in turn implies straight lines. It is plausible that the drivers for rectilinear layouts may have been man's horses, mules, and carts as much as man himself, spurred by the growth of settlements.
The creation of the Radburn pattern is attributed to Clarence Stein but has a lineage of ideas that preceded it in Raymond Unwin and Barry Parker's work that included the use of cul-de-sac and crescent street types. In contrast to the scarcity of records that obscures the original rationale for the grid, the reasons for the Radburn pattern have been articulated clearly in Stein's writings and those of his predecessors.
"Radburn" now denotes a street network configuration. It signifies a departure from the strict orthogonal geometry and regularity of the grid and a distinct approach to laying out new districts. As a system, it can be described more accurately as a "cellular" network that has a characteristic hierarchy of streets as distinct from identical streets intersecting at regular intervals. Its derivatives and idiosyncratic imitations are often characterized as "cul-de-sac and loop" patterns highlighting the distinguishing street types that are used systematically in this network. A second term equally uncharacteristic is "suburban". This association of a pattern with a location is inaccurate and unintentionally misleading: entire early cities such as Cairo and Fez are structured on this pattern whose newer suburbs follow the grid reversing the urban/suburban relationship. "Suburban" is also devoid of geometric descriptors of the pattern. These shorthand expressions conceal the variety of patterns that emerged in the 20th century that are decidedly neither grids nor "Radburn" and the "system" aspect of the pattern. The "loop and lollipop" label may be a more applicable descriptor of later interpretations of the Radburn model that appear to lack structure and to overlook key elements of the original concept such as its emphasis on pedestrian priority, for example. The pattern's systematic use of the cul-de-sac and loop is decidedly linked to automotive mobility as a means of controlling and guiding its flow. The Radburn pattern is a complex system; more than a series of identical orthogonal city blocks in a linear progression. It rests on a functional program plus an intentional picturesque aesthetic: it avoids straight lines, limits four-way intersections and shuns repetitive blocks all of which enhance its picturesque imagery. To facilitate the discussion, the name "Radburn-like" or "Radburn-type" will be used in the subsequent sections.
Criticisms of the prevailing network patterns
The two dominant network patterns, the grid and Radburn, have been debated by planners, transportation engineers and social observers on grounds that include issues of defence, aesthetics, adaptability, sociability, mobility, health, safety, security and environmental impact.Defence, aesthetics, and adaptability
The first known criticism of the grid was put forward on the grounds of defence that became irrelevant following the prevalence of the cannon. Aristotle argued that the old maze-like street pattern, which preceded the grid, made it difficult for invading troops to find their way in and out of the city, Alberti also expressed the same view 1500 years later and added the advantage of a superior visual effect of the organic pattern over the grid.A second criticism was put forward most forcefully by Camillo Sitte on aesthetic grounds. He argued that grids lack variety and, consequently, are uninteresting and can become oppressive by their monotony. This argument has been undermined first by the potential variety of grid dimensions that can be used in combinations such as appear in many city plans. More importantly, ground observation of cities shows that the mix of buildings and their varied street alignments as well as open spaces with their size variations coupled with constant redevelopment, suppress the monotony of the grid. Nonetheless, 20th century planners shunned pure grids and implicitly endorsed C. Sitte's ideas on the need for a picturesque streetscape. This tendency is generally based on an intuitive aesthetic ground; that people dislike long open street vistas and prefer those that terminate. Recent subdivision or town layouts such as Poundbury, Seaside and Kentlands consciously avoided the homogeneous grid and its open vistas.
A further criticism of the grid focuses on its unsuitability for uneven, variegated terrain. Its application in sites such as Priene, Piraeus, San Francisco, Saint John, NB and others severely limits general accessibility by inadvertently introducing steep slopes or, in certain cases, stepped road sections and creates construction difficulties. In cities with intemperate climates this limitation is accentuated. Moving in a straight line uphill becomes arduous or, occasionally, impossible, particularly for non-motorized wheeled means of transport.
A Radburn-type network inherently includes a variety of city blocks and terminating vistas and, consequently, preempts criticism centered on monotony and lack of end-closure. Its unconstrained geometry adapts easily to topographical irregularities and geographical features such as streams, woodlots and natural ponds. As neither the alignment nor the length of neighbourhood streets need to remain constant, this model gives planners considerable latitude in laying out a network.
Two newer aesthetic criticisms of the Radburn model emerged in the 1980s: the absence of a street "wall" or "enclosure" and the repetitiveness of housing unit forms as found in suburban districts. Both these criticisms can be understood as a misapplication of aesthetic norms on socio-economic outcomes. The spaciousness of housing developments at the city's edge echoes the spaciousness of contemporary houses and are both driven not by aesthetic intent but by economic prosperity. Judging the visual outcome of prosperity using historic streetscape criteria of cities with a different socioeconomic makeup would make the verdict predictable and practically meaningless.
Moreover, the "street wall" and "enclosure" criticism of the Radburn pattern applications are undermined by observation of city districts new and old. Close examination would reveal that these spatial qualities are inextricably linked to housing unit and population density as well as construction technology and are not necessarily the outcome of a street pattern: The higher the habitation density of the street the closer and taller the buildings have to be to accommodate more people. A street pattern does not induce either unit density or the visual wall effect. For example, in earlier cities with labyrinthine street layouts, analogous to some contemporary suburban districts, residential buildings were agglutinated creating an entire perimeter wall around the city block with few perforations for reasons of security, safety and a heightened sense of privacy, not streetscape aesthetic. Conversely, early founded cities in North America, where land was almost free but construction costly, are depicted with generous lot dimensions and very small houses on them that created a weak "enclosure" vertically and horizontally. At both ends of the streetscape scale, very proximate and very sparse buildings, socio-economic factors drive the outcome.
Regarding repetitiveness of housing form, ground observation shows no relation to street pattern. Homogeneity correlates better with methods of production. Early agglutinated housing forms as in Pompeii and Tunis, with vastly different street patterns, presented no face on the street by which design differences could be discerned; plain and luxurious houses had the same nondescript, blank street face. In recent times, older streets of more recent cities with a grid show considerable replication, based on vernacular and pattern books, as do newer streets on the fringe, based on industrialization. What has impacted the urban landscape appreciably is the scale of production: many single operators in earlier periods with small yearly output versus few large corporations by mid-20th century with high annual production volumes. Inevitably, the larger the operation is, the greater the economies of repetition are. Similar house models can be found not only in the same subdivision but across states and even nations. For example, veterans housing that was built in Canada consists of two or three models that were repeated in neighbourhoods and across the country. The most impressive effect of large-scale production is starkly visible in Levittown, New York and in social housing projects, where the State also aims at economies of scale. In the case of early Huguenot settlements, sameness of houses on identical grid patterns was pursued as a means of expressing the social equality of all inhabitants – a community goal.