Quantifying the Contextual Influences on Road Design

This article describes the COSMA (COntext Sensitive Multimodal Assessment) method that uses contextual information to develop road infrastructure recommendations for the purpose of improved road design. The method uses a GIS-based Spatial Multi-criteria Analysis (SMCA) that is combined with statistical clustering techniques to identify contextually similar areas along arterials. The context is defined in terms of a range of land use, socioeconomic, environmental, and transportation information, presented spatially, which are used as inputs to the SMCA. The results of this analysis describe the relative suitability of different modes of transport to locations along an arterial route. Clustering the output of this analysis allows for sections of the route with similar contexts to be identified. The attributes of these clusters are then used to derive descriptive statements of contextually appropriate operational conditions for each mode in a particular section of the route in terms of access, right of way, and independence of movement. These can be used by road designers to develop proposals for road infrastructure design. We demonstrate the workings of the method for an arterial road in Cape Town, South Africa. The method described is explicitly multimodal and sensitive to the variations in local context. It can be used by planners and roads authorities to provide additional perspective on road user needs and facility provision, and introduces quantification, and the concomitant benefits thereof, to the largely qualitative field of Context Sensitive Design.