Fused Grid

The fused grid is a street network pattern first proposed in 2002 and subsequently applied in Calgary, Alberta (2006) and Stratford, Ontario (2004). 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 self-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.

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 has been articulated clearly in Stein's writings and those of his predecessors.,

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