Tools for addressing transport inequality: A novel variant of accessibility measurement

Accessibility is widely thought the most appropriate reference point when assessing transport inequality, a fundamental consideration of the liveable city. But definitions of accessibility vary and often either trivialise or overcomplicate the concept, with the result that decision makers lack a representation of it that is sufficiently accurate and at the same time sufficiently straightforward. A response is offered in this paper: the Index of Personal Travel Impact (IPTI). IPTI is an estimate at the individual level of the relative impact of desired travel, reflecting the time taken and real financial effect, and is expressed as an amount per unit distance. It is calculated using the journeys an individual would like to make (as opposed to those they actually make or those that an authority might assume “important”) and reflects the specific characteristics of the individual (e.g. car availability or mobility impairment) and of the journey (e.g. the need to arrive by a given time). It therefore serves as a good individual-level representation of the relative ease/difficulty of travelling.The rationale for IPTI's formulation is described in detail and the measure's strengths and weaknesses discussed. The practical feasibility of calculating IPTI is explored through description of a small pilot which produced encouraging results, and through a discussion of the potential efficiencies offered by the increasing availability of large data sources and online journey-planning tools. IPTI's potential applications are then discussed: first, it could provide an intelligible way of demonstrating the differing extent to which people face mobility barriers, which could be useful where an attempt is being made to address inequality. Second, IPTI could inform the appraisal process by showing the distributional effects of a given scheme upon individuals' relative capacity to travel. The paper concludes with recommendations for further research.