Testing a gravity-based accessibility instrument to engage stakeholders into integrated LUT planning

In this paper we present the results of a structured-workshop involving private and public stakeholders to test usability of gravity-based accessibility measures (GraBaM) to assess integrated land-use and transport policies. The research is part of the COST Action TU1002 “Accessibility Instruments for Planning Practice” during which different accessibility instruments where tested for different case studies. Here we report on the empirical case study of Rome In the first part of the paper, the accessibility measure adopted and the tool in which these are implemented (i.e. GraBaM) are presented. The used accessibility measure is defined in literature as “gravity-based”, since it can be derived from “gravity-type” trip distribution model (Hansen, 1959). In particular two types of accessibility have been considered, referred to as “active” and “passive” accessibility (Cascetta, 2009). The active accessibility of a given zone i is a proxy of the ease of reaching the activities/opportunities located in different zones j of the study area for a given purpose (e.g. workplace, shopping) moving from i. On the other hand, the passive accessibility is a proxy of the opportunity of an activity located in a given zone i to be reached from the potential “consumers” coming from all the other zones j of the study area for a given purpose. Such definitions do consider the accessibility of a given zone as a sum of the generalized travel costs between zones itself and the other zones of the study area, weighted by an attraction term representing either the opportunities to be reached in the other zones (in the case of the active accessibility) or the potential “consumers” of the opportunity located in the given zone (in the case of the passive accessibility). The tool integrates the calculus of these accessibility measures with the production of accessibility maps, allowing easily changing parameters and visualizing the outputs, with the use of GIS, which provides easily spatial data entry, management, retrieval, analysis and visualization. In particular the accessibility maps represent for each traffic zone in which the study area is divided, the accessibility measure, also allowing overlapping it with other geographical data. The GraBAM (Papa and Coppola, 2012) tool can be integrated in comprehensive Land Use Transport Interaction (LUTI) modelling architecture, simulating the impacts of changing accessibility on the spatial distribution of residential and economic activity as well as on dwelling prices (Coppola and Nuzzolo, 2011). In doing so it can also assist urban planners in identifying optimal locations for new development areas and can support the analysis of the real estate market dynamics due to changing land-use and transport variables. In the second part of the research the accessibility tool have been tested within a structured workshop involving public and private stakeholders, according to a four-step protocol (te Brömmelstroet et al, 2014 ) defined within the COST Action. The main goal was to evaluate usability and applicability of the tool in the current practice of the practitioners involved in the experiment, and, at the same, time to generate an experiential learning-cycle process within the group of people (researchers and practitioners) involved. The experiment was set in Rome, and involved a panel of experts in the fields of Land Use and Transport planning. Different backgrounds guaranteed different perspectives on the usability of the instrument, both transport and urban planners from the private sector (consulting), public sector (municipal planning offices) and academia were involved. The heterogeneity of the group was a key factor for the success of the workshop. Nevertheless, this required a more complex preliminary activity to organize ‘customized’ pre-workshops with selected groups of participants. The paper describes the experience and give answers to the following questions enriching the final outputs of the COST Action: what the tool’s developers learned and how the tool has been improved after the test; what practitioners learned from the experience, also in relations to their background and to which extent the test had a direct impact on the local context and on the ongoing planning processes.