IResidential Street Management in South Australia BY W BARRY HAGAN AND SAM E AMAMOO

F the early 1900s to the late 1940s, road networks in South Australia were developed on the rectangular grid system as an extension to the original planning of early towns and villages. With the advent of the automobile and sealed pavements, most local government authorities constructed a sealed central strip approximately 6 meters wide with wide footpaths and verges around existing street trees. As traffic volumes increased pavement reconstruction or widening took place, and curbs, gutters, and drainage systems were installed. A hierarchy of roads and streets, often defined by carriageway widths, became evident on the original grid network. In the late 1940s to the late 1970s curvilinear road systems with offset intersections and an imposed hierarchy became the norm for development in residential subdivisions. Major road standards were applied to the planning, design, and construction of all streets and roads, and allowances were built in the pavement widths and depths to provide for continuing traffic growth. Current practice generally tends to follow the preceding principles with some modifications to achieve more cost-effective designs and to minimize some of the operating problems evident with such systems. The rectangular grid system produces a local road network with high connectivity and a large number of four-way intersections. Such a system does, however, attract nonlocal traffic seeking to avoid congestion and delays on the major road system. The four-way intersections increase the potential for a greater number of and more severe traffic accidents, with higher risks to the local users. The straight road alignments, often with relatively wide carriageways, encourage vehicle speeds that are unsafe in the residential environment. The conventional road hierarchy classification based on access and nonaccess functions (see sidebar) is difficult to apply on streets in the rectangular grid network. More modern layouts, based on the collector road principle, raise safety and amenity problems of a different kind. There is a conflict of function on collector roads, which must perform both the access and the traffic movement functions. That is, collector roads cannot be easily classified as either streets or roads; they serve both functions. These collector roads are generally of considerable length, often with relatively wide carriageways and sweeping curvilinear