Representing Planning Policy in Land-use and Land-use/transport Modelling
A Dobson, D Simmonds, T Simpson, P Minta, David Simmons Consultancy Ltd, UK
This paper considers issues of representing planning policies in land-use modelling. The examples relate to the authors? UK work with the DELTA package, but the issues are general.
This paper considers the range of issues surrounding the representation of planning policies in land-use and land-use/transport interaction modelling. The examples are related to the authors? work in the UK with the DELTA package, but the issues are general and relevant to other models and to other planning systems.
The paper first considers why we need to represent planning policies in modelling, the most common reasons reason being the influence or control it exerts on future development, which is important to assessing future travel demand; but increasing, because there is also a need to test and appraise alternative planning policies. The impacts of planning policy are complex - it is not correct simply to add the occupants of new housing and new employment sites to the existing totals, as has often been done in the past.
The paper then moves on to the critical question: how we represent planning policies? This is mainly through how much development (by zone and type) is either imposed upon the model or allowed to be developed if selected by the choices in the development model. This needs to cover a sequence of different time periods:  the immediate future, where detailed information on current and imminent development proposals should be available;  the short to medium term, where for some land-uses there are fixed allocations of specific sites in published plans;  the medium to long term, where allocations may be less specific, and are subject to review;  the very long term, where even long-term planning documents do not usually allocate development.
Issues arising around this include  the question of representing housing as dwellings, as floorspace or other variables such as number of rooms;  what to do where policies are reactive rather than allocative, and in particular the treatment of redevelopment in modelling and analysis;  the potential requirement to estimate ?additional allocations? of development to ensure that the planning policies in total are compatible with the economic and demographic scenarios used in the modelling; and  the problem that transport planning, and associated environmental calculations, such as projections of carbon emissions from the land transport sector, assume that land-use policy is known. In practice policies are subject to review (perhaps we should forecast how such reviews will respond to future conditions?), and the time horizons of even the most long-term spatial plans are generally closer than the time horizons required for transport and environmental analysis.
Some recent models also consider of quality and public realm effects; we will describe how these are treated and the kind of results that can emerge. We give examples of testing different spatial policy inputs, illustrating the fact that the impacts of transport interventions can be significantly different depending whether the planning policy inputs are sufficiently liberal to allow additional development to follow increases in demand. From the discussion and examples we draw conclusions regarding  the value of trying to represent planning policy;  the importance placed on the (very) long-term in some forms of transport appraisal -especially the UK WebTAG requirements - whilst recognizing the importance of trying to consider the very long-term for environmental reasons; and  likely ways forward to improve the representation of planning in modelling. We will consider these from the point of view of client organizations and local planning authorities as well as from the modelling and analytical perspective.
Association for European Transport