The Co-Evolution of Land Use and Road Networks

Transportation and land use are interdependent shapers of urban form. First, changes in land use alter travel demand patterns, which determine traffic flows on transportation infrastructure. Second, changed traffic flows drive the improvement of transportation facilities. Third, new transportation facilities change the accessibility pattern, which drives the re-location of activities and land uses. During this process, both transportation and land use are evolving constantly, leading to salient spatial transformations such as agglomeration and centralization over space and transportation networks. For example, as cities evolved in the first half of the 20th century, we saw a concentration of activities and development at the centers of cities. As freeways were constructed from the 1960s, roads also became more differentiated with regard to their functional designs and running speeds (certainly in the pre-auto era most unpaved streets were equally slow, with paved streets and highways and then freeways, some roads got much faster). Urban agglomeration and differentiated highway networks are referred to as hierarchical systems in this study.In the context of the co-evolution of land use and road networks, this paper in particular examines the degree to which the dynamics of land use is reinforcing or counteracting hierarchies of road networks. By this we ask will a more hierarchical distribution of activities lead to a more or less hierarchical road network? Observation of historical evidence does not lead to a clear conclusion, as the development of a hierarchy of transit systems during the streetcar/subway era was accompanied with a concentration of development (especially employment) in the center of cities (from an undeveloped state), while the development of a hierarchical road network (from an underdeveloped and largely undifferentiated street system) occurred when those same cities were decentralized from a highly developed state. This paper aims to examine this question in a simulation environment with controlled initial conditions and quantitative measurements of spatial hierarchy.The remainder of this paper is organized as follows: the next section presents a review of related literature, which is followed by an introduction to the simulation model developed for this study. Then the experiments are outlined, and results are reported, and some sensitivity analyses conducted. The conclusions summarize the findings and suggest future directions for research.