URBAN FORM
2.2.2.3. The Radial System
In this urban form there is a single dominant focus which is centrally placed in the region with a series of major paths of circulation which lead into it. These paths are ribbons of development and between these are large wedges of open space. These paths are connected by a circumferential path, and at the point of connection a smaller centre, or node, is formed. As part of a hierarchical structure, these centres
Page | 24 are less important than the major centre toward which all paths run in this form.
The radial paths are linear sequences which all end in the major centre but the distance covered is scaled by the rhythm of passing through the minor centres on the circumferential path. The radial pathways pushing outward eventually lose momentum and the opportunity for satellite communities exist at the ends of these.
This type of urban form can take the shape of a star, and it generally grows outward along its rays of radial paths, although as the observer moves further from the major centre, development is linear in form and becomes isolated from the other radial paths. Lynch says that the major centre, or other important centres, can grow together by
“rolling” along the path which connects them.
There are several problems relating to the Radial Form. One is that it becomes difficult to maintain a sense of direction on the
circumferential paths due to its endlessly curving nature. There is also the problem of a lack of ability to adapt due to the large focus of energy on the major centre. Problems in accessibility arise from the inherent principle of convergence, although this feature allows mass transit systems to operate very efficiently due to the high density of people living and working close to the radial paths (Banerjee, 1990:
79-80).
Figure 14: The radial system involves a single major centre. Minor centres occur at intersections of the major routes which lead into the major centre, and the minor routes which encircle the major centre.
Page | 25 2.2.2.4. The Grid System
This system is based on the general rectangular grid of major paths and performs best in terms of efficiency and of sensing direction. The spacing within the grid may vary, but the principle is that paths run parallel and perpendicular to one another and these two sets of paths are distinguishable from each other. There can be hierarchical ranking to a certain degree among the paths, with the dominant path being the most important.
There is a recurrent rhythmic sequence which occurs along these paths by those which are perpendicular to the direction the observer is travelling which gives a sense of scale.
The Grid System is a very basic form which has clarity and indefinite coverage whilst being able to organise a complex and large
environment, together with being able to adapt to changes in function and circulation very well. The centres in the system can be varied in their relation to the grid; they have diverse characters and functions whilst they are not isolated from one another.
Foci are found at the intersections of paths, but do not straddle them.
The location and hierarchical rank of the foci depend on the crossing of major paths. There is a difficult relationship between the foci and gridlines because the centres have to lie beside the lines so as to not to interrupt the path flow. Major circulation works more efficiently if access to the major centres occurs between the major intersections, rather than at them. This causes a sense of isolation between the grid
Figure 15: The grid system functions on logic and efficiency of space.
Page | 26 and the rest of the spatial structure. As with the radial form, densities decrease as the distance from the foci increases.
The grid system has its positives and negatives surrounding it. The major positives are that it relates well to growth and change, functionality is very flexible, flow changes can be accommodated, and the form allows for very efficient use of land. The negative is that “it is an endless, repetitive form, rather than centrally oriented”
(Banerjee, 1990: 81-2).
Many cities are made up of a composition of two or more of the above urban forms, but Lynch proposes how best to utilise each form to impact positively on any existing city – not considering the costs involved. The following are a few of his proposals (see figure 16):
a) A rectangular grid of limited-access freeways. These would pass near, but not through, existing centres. It would be important to maintain visual contact of the centres and open spaces from the freeway. Transit lines would run on the same grid at the freeways, and these would loop off the grid to pass through the centres.
b) Arterial streets in the existing city would be gradually relocated and improved. These streets would run from centre to centre and along them would be a concentration of special non-central uses.
c) Dispersion of central functions would be encouraged, but only to other central locations. Where necessary, new multi-purpose centres would be supported, and would be aligned to the arterial street network. It would be important, however, to maintain the integrity of the original centre because its degree of specialisation would be desirable. All centres in the regional system would maintain their concentration, mixed use would be encouraged, and each centre would have its own local movement system. Each centre would have its own recognisable identity complete with landmarks, entrances and focal points.
d) Densities are recommended to be kept relatively low, but not uniform, with an increase along the arterial streets and particularly near the centres. Central functions would be encouraged to remain in
Page | 27 clusters and access-oriented functions would be located on arterials, whilst other uses would be allowed to be placed freely. Diversity and individual action would be most encouraged (Banerjee, 1990: 83-85).
The above proposals show that Lynch encourages cities to possess multiple centres of great diversity, but it also shows that he is not afraid of the highway and the freedom of movement of the motor car. Although his system does involve centre-to-centre movement of mass transit, this network would run side-by-side with highways which is noble, but the superior travel times of the private car to mass transit may have the upper hand in an apparent
competition.
Lewis Mumford agrees with Lynch’s embracement of the highway, although he says that they must be designed correctly and sympathetically toward the existing urban fabric. It is clear from his writings that he feels that the highway is destroying the urban landscape, however he does make some interesting points. He says that the “motorway has taken the most valuable recreation space the city possesses,” not only by using land which could be used for other things, but also by cutting off urban features (Mumford, 1964:
183).
Figure 16: This diagram is based on the above mentioned theories of Kevin Lynch. The scheme is anchored on the freeway and railway grid.
Page | 28 Mumford draws a comparison between train and private vehicle traffic
crossing London Bridge. He says that the railroad could carry 50 000 people across the bridge in one hour, whereas the best freeways can allow 4 000 to 6 000 cars to pass a single point per hour. Freeways take up a much larger space than a railway does, but cannot compete with the rate at which the railway can carry passengers (Mumford, 1964: 186).
Mumford draws another comparison, this time between pedestrians and cars.
He says that moving 100 000 pedestrians could be moved from point A to point B in half an hour, but it is unknown how long it would take to move the same number of people travelling in cars between the same points (Mumford, 1964: 186).
It is clear from these comparisons how the issue of congestion in city centres arises.