The paper highlights the shortcomings of current procedures and proposes a way forward which accommodates the transferred and pass-by trips created by a competing, retail market. The paper briefly describes the history of retail development as a three stage process of firstly large, one-stop shopping foodstores, secondly non-food, retail warehousing and thirdly the current large, multi-use retail centres. The shortcomings of current methods to cope with the changing scene are highlighted with respect to the influence of catchment area characteristics and interacting, competing catchment areas. The concept of a finite but dynamically evolving food market is discussed and the implication of this on retail trips. It is argued that there are three basic trip types: new, transferred and pass-by. Transferred and pass-by trips are not new to the network and must be treated differently. Research work in the United States of America, which supports this view, is discussed. These three trip types are a simplification of the actual patterns which include, for example, pass- by trips diverted from other routes. The pass- by trips may also be transferred trips from other retail centres. The effects of pass-by diverted and undiverted and transferred trips on traffic impact analysis methodology is discussed. The percentages of transferred and pass-by trips are high and the effects on the highway network are significant. It is suggested that the analysis can be broken down into two basic parts: the micro-network and the macro-network. The Micro-network analysis involves a better understanding of these effects on local turning movements and the consequent effects on local junction capacity. The macro-network analysis involves appraising the benefits and disbenefits on the area-wide urban network. The net effect of the proposed development may be a net reduction in journey costs with a subsequent improvement in accident rates. The macro-network analysis requires a strategic area model matching retail trips generated at the zonal level to retail centre arrivals. Current research at Napier Polytechnic of Edinburgh indicates this is achievable. Underlying this development work is the building of better trip generation databases to include catchment area characteristics, store characteristics and information on trip types. Napier Polytechnic is currently developing an existing trip generation database, in collaboration with Scottish local authorities, to include these factors. In addition work is being carried out relating to the reappraisal of traffic impact analysis in line with the concepts proffered in this paper
Abstract