Dewar (2011) pointed out that that the corridor planning approach facilitates more intensive activities, non-motorized and public transport, stimulates small business growth, promotes land use mix and pursues equity and urban integration vigorously. It spatial form represents a broad band (approximately a kilometre wide) of mixed uses that are continually intensifying around one or more hierarchically interlinked system of transportation routes or spines that accommodates public transportation. These continuous transport routes in urban areas represent energy arteries that carry flows of people, goods, services and finance and the greater the volume of movement along the route the greater the potential market and they tie together a number of local areas, which they pass and act as integrators. As a result, no one area is entirely independent on its own resources but they support each other in a symbiotic way as illustrated in Figures 24 and 25.
As discussed by Dewar (1994, cited in Provincial Planning and Development Commission (PPDC) 2008) research report, Figure 24 illustrates an inward orientation of local areas with intensive activities in the centres which was a dominant model in South Africa (SA) for the past fifty years. These centres were dependant on their own resources to support the intensive uses of the public and depended on public
1 It is noted that the spread of HIV and AIDS in Southern Africa and elsewhere has been directly linked to the transportation corridors particularly the long distance routes used by trucking companies that in turn are utilized by sex workers.
support for their viability. Within this context insufficient thresholds, lack of public support to maintain essential activities and inaccessibility of essential services to people living in the cell resulted in poverty, degradation and low quality of life. However, in Figure 25 the cells are oriented towards the transport routes, which are the primary arteries of access. As a result, local areas support each other by contributing to the system hence the levels of services are higher and better. Furthermore, access to shared services are more convenient through public transport and walking and is therefore more sustainable to channel investments and increase densities due to higher thresholds.
Figure 24: Corridor Growth Figure 25: Corridor integrating Local Areas
Source: Uytenbogaardt, Dewar and Todeschini (1997, cited in PPDC, 2008)
Dewar (2011) indicated further that intensive activities do not occur evenly along the corridor but tend to agglomerate or cluster according to the relative accessibility of points hence, the pattern is one of
“beads on a string”. Dewar (1994, cited in Provincial Planning and Development Commission (PPDC) 2008) argued that, the greater the accessibility to economic and social facilities at a specific point the greater the tendency to attract more intensive uses. At an intersection, an arterial with limited access represents a low accessibility point. The pattern therefore is one of uneven development in the growth of clusters at various points as illustrated in Figure 26 which results in the development of a hierarchical nature of beads or nodes) and system of routes or corridors.
Figure 26: Corridor Growth
Source Uytenbogaardt, Dewar and Todeschini (1997, cited in PPDC, 2008)
Furthermore, successful corridors are two sided at places where there is an agglomeration of intense activities and pedestrians are able to cross on either side quickly and easily as indicated in Figure 27 where roads are narrowed or pinched. The advantage of a hierarchically differentiated (defined in terms of continuity) system of routes along the corridor is that a complex pattern of land values emerge that allows all activities being large, small, formal and informal to be accommodated within the system.
Figure 27: Corridor and Node Hierarchy
Source: cited in Logan, (page 23, 2012)
Martins (2001) states that a distinction therefore exists between corridors, spines and activity streets.
An activity corridor is at a metropolitan/city scale approximately two kilometres wide comprising of mixed uses, high density urban activities concentrated along public transportation routes i.e. large inter- urban corridors. At the centre of an activity corridor is an activity spine, which carries major public transport. It provides locations for intensive mixed uses that function at a district level, and is at medium scale. The activity street occurs at a small scale, residential local level and has lower levels of market thresholds (See Figure 28). Furthermore, major mobility corridors accommodate linear routes such as railways, freeways, large shopping areas, industrial parks, social, cultural and sporting facilities.
Corridors can therefore be used as tools to structure where and how activities take place based on access being the main element however, in order for corridors to function efficiently there has to be linkages between key structuring elements as identified above (i.e. nodes and corridors).
Figure 28: Structuring Elements of a Corridor
Source: Cape Metro Council, 2000 cited in Warner and Verster, 2005
Dewar (2011) listed some advantages that flow from corridor planning namely:-
They promote decentralisation and reduces movement and carbon emissions;
The high land prices along the corridor ensures a wide range of competitive activities;
Facilitates a symbiotic relationship between large and small activities where larger enterprises are the primary generators of movements and are located at more accessible locations whilst
the smaller activities locate at interceptor locations and feed off the larger which makes corridors play an incubator function for micro-enterprises;
They discourage monopolisation of larger activities;
Adapts to growth and change of uses quickly and easily;
Promotes equity by providing access to various activities through the use of public transportation that is channelled through the corridor;
Benefits the principle of urban integration i.e. local areas and land uses (i.e. residential, commercial, recreation) that promotes convenience; and
Combats fragmentation and increases integration i.e. ties many local areas into an integrated system.
An evaluative study undertaken by the Ekurhuleni Metropolitan Municipality (2004) into development corridors indicated that the main elements of a development corridor are: a distinct road hierarchy;
mobility spines; activity spines; open space system; connected nodes (varying in types and sizes), and defined start and end as graphically depicted in Figure 28 above. The concept reinforces the importance of the fact that it occurs over a period of time, which depends on critical factors such as; anticipated timeframes together with phasing of developments; the availability of infrastructure services; the rate at which development occurs; prioritising of linking roads with transportation and mobility and the supporting of these roads with strong nodes. In addition, the PPDC report (2008) also highlights generic space types that can be found in corridor initiatives namely:-
Major Metropolitan Gateways;
Secondary Gateways;
Pinch Points;
Activity Street;
Dual Access Boulevard;
Interchanges;
Station squares;
Structures public transport stops;
Sports or recreational forecourts;
Public or civic forecourts; and,
Structured non-motorised transport (NMT).