Tradionally, the form of the road network on a regional scale strongly depends on natural constraints and/or the historical rural occupation patterns. For example, in the Dutch province of Drenthe, several features of the triangular network can be observed through the old Sachsian settlement pattern. Principally, there are two basic shapes: radial and tangential (the somewhat confusing terms functional and geometric network are also in use). In a radial network, the roads start from the center village or town and go into the surrounding rural area. This system is found in areas with natural barriers such as hills, mountains, or rivers and/or in areas where the occupation lasted relatively long (Fig. 3.3A). Adequately expanded radial networks provide access to the formerly fairly inaccessible mountainous areas. In contrast, a tangential network is applied in more or less homogeneous areas, occupied during a relatively short period. They are characterized by a clear, easily expanded structure. This type of network is suitable in areas with intensive agriculture and forestry. Its chessboard structure is well known in the United States. It also occurs in both historically (Fig. 3.3B) and more recently constructed reclamation areas (e.g., The Netherlands), in extensive agricultural regions (e.g., eastern Germany), and in lowlands of mountain regions (e.g., Switzerland).
In practice, adapted forms of these basics appear. Radial networks are shaped either as a branched structure or an "antichessboard." A grid structure introduces hierarchy into the basically unhierarchical tangential chessboard network . Figure 3.4 shows the most important advantages and disadvantages.
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