Chapter 3 – Part four: A central metropolitan block

The ‘module’ of the network

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In theory, the smaller the module or basic dimension of the grid (when it is square or nearly so) the greater is the capacity of the grid to distribute or accept vehicles to or from the areas. This is simply because, with a small grid, there is a greater length of primary road for each acre of area that is served. But, for two main reasons, there is a limit to the smallness of the grid. In the first place the amount of traffic that can be transferred between area and grid is governed by the number and capacity of the interchange ramps, and there are certain minimum distances apart that these can be placed for reasons of flow and safety. The second reason is concerned with the fact that an area also generates local trips, and the smaller the grid the more these local journeys tend to be thrown onto the grid, until there comes a point when the additional load outweighs the gain in capacity.