Modelling Pedestrian Accessibility Using GIS Techniques to Assess Development Sustainability
J Colclough, AECOM, UK; E Owens, West Northamptonshire Development Corporation, UK
A GIS pedestrian accessibility model was developed to provide added sophistication to traditional methods of assessing journey times. This has helped assess the sustainability of proposed developments.
West Northamptonshire Development Corporation oversees development in their jurisdiction, with the aim of ensuring new homes are delivered sustainably. A key aspect of this role is to minimise the potential impact of additional trips generated from the proposed developments. An effective method of achieving this aim is to promote walking as a means of transport by ensuring each site has adequate accessibility to key facilities. This has traditionally been undertaken by mapping a two kilometre buffer around the destination using Euclidean distance. Whilst this provides a quick and easy assessment, advancements in technology (principally through the development of Geographical Information Systems), has provided the means to add sophistication to this analysis. This was particularly important for the assessment in West Northamptonshire due to the topology of the development sites and the subsequent impact on walk speed. In addition, the demographic profile of walkers was significantly different for certain destinations, changing the speed profile and thus journey time. Therefore, a model was created that considered these two main factors.
Faber Maunsell developed an innovative GIS pedestrian accessibility model using ESRI ArcGIS software. The model consisted of a footpath network that was comprised of individual links that were attributed a walk speed for both directions. This was achieved by calculating the gradient of each link using Ordnance Survey data. A review of the literature identified one study in particular by Finnis and Walton (2007) that quantified the relationship between gradient and walk speed. This information was validated on site by walking a series of routes to determine the average walk speed. The GIS software was customised using ArcObjects and VBA to automate the calculation of the gradient for each link. Finnis and Walton also provide a summary of average walk speed by demographic group. This was used in conjunction with the speed-gradient relationship to determine a link speed by demographic profile. The model was then used to calculate walking isochrones to each destination based on the trip purpose. The isochrones were drawn at key threshold times, identified from the National Travel Survey (NTS). Each destination was assessed to determine the percentage of dwellings that were within each five minute isochrone. An additional isochrone was added that signified a reasonable walk time threshold, as identified using the NTS. The destinations were ranked based on the percentage of dwellings within the threshold walk time. This provided an overall assessment of the pedestrian accessibility levels.
Through the use of innovative GIS modelling techniques, sophistication was added to the assessment of pedestrian accessibility. This improved the accuracy of the results in comparison with traditional methods. The results of this study have been used by WNDC to assess the potential sustainability of development sites in West Northamptonshire with the aim of reducing the number of car trips from the site. This has informed discussions regarding land use and public transport provision.
Association for European Transport