Estimating the spatial distribution of industry within an urban Region

Abstract

It has become the practice of traffic engineers to base the design of transportation facilities upon predictions of future land use. Although the relationship between traffic generation and land use has been well established, techniques for the accurate prediction of land use are much less reliable. The planning sequence usually follows this pattern: i) future land use is predicted, 2) the traffic generating and attracting characteristics of the predicted land uses are calculated, 3) the traffic generated or attracted is "assigned" to destinations or points of origin, 4) facilities are designed to handle the predicted traffic. The United States Department of Commerce, Bureau of Public Roads, has established a complete "transportation planning package" including supporting traffic analysis programs that follows this basic sequence of operations. 2 Some of the computer programs used in this process are now quite detailed and sophisticated. For instance, provision is made for simulating vehicular movement over the entire future highway system including allowance for differential delays for vehicles making right or left turning movements. However, none of this elaboration should obscure the difficulties in making the prediction process reliable. The land use forecast is the fundamental structure to which the elaborate filigree of the transportation planner's artis applied. Several years ago the predicted land use patterns "put into the traffic models" were the official General Plans of the municipal governments. Although this is still being done in some places, the official plans are notoriously unreliable indicators of urban development. Norton E. Long has termed them "civic New Year's resolutions." It is now becoming common to create these basic predictions of land use through the use of mathematical models of urban development. Generally the task of modeling urban land use change is broken down into land use components such as "Residential," "Commercial, " "Industrial," etc. In programs that take this approach the model process is usually ordered in such a manner as to locate industrial lands first. This is not simply a matter of convenience; the location of industrial land plays a significant role in such models. The location of residences is thought to be greatly influenced by the location of work sites. In some model schemes the "journey-to-work" assumes an almost metaphysical significance in that it becomes the sole determinate of residential location. The residential locations may be in turn asserted to "cause" commercial locations. The model system being developed for Santa Clara County, California, follows this general ordering of events, although the relative significance of any one type of land use upon the location of any other will be established analytically. Still, it is thought that the location of industrial land (jobs) will profoundly influence the subsequent forecasts for other land uses. The location of future industry will also affect the transportation planning