Accessibility, freedom of choice and diversity

Most previous work on accessibility has examined either minimum thresholds of opportunity or quantity of opportunity, often with a social equity perspective. Complementary to both these approaches is the degree (or diversity) of choice offered by alternative opportunities. Several authors have considered access to diversity to be an important aspect of quality of life. However, with a few exceptions, this concept has been overlooked in the transportation planning literature. At the neighbourhood level, the provision of diversity in terms of both land-use and social mix is now a key policy objective. Amongst other things, it is argued that local diversity promotes more sustainable travel patterns by encouraging walking and supporting good public transport connectivity. Measures of diversity have been included as explanatory variables in a number of studies of travel behaviour and evidence in support of these arguments has been found. However, the measures used are, on the whole, based on small-area attributes, (arguably) offer a limited interpretation of diversity and take no account of the diversity of the wider city context. Moreover, these measures only reflect the supply of local opportunities and take no account of the preferences of individuals or the constraints placed upon them. This paper will draw on the extensive literature which exists on the definition and measurement of diversity in fields ranging from economics to ecology to develop quantitative measures of access to diversity. Stirling (2007) identified three dimensions of diversity – variety, balance and disparity – and the extent to which the measures capture each of these dimensions is examined. The access to diversity measures are consistent with and can be employed alongside commonly used measures of accessibility, such as cumulative opportunity, gravity model and utility-based measures