Household Space-time Accessibility Measures: a New Theoretical and Application Framework
O Ashiru, Imperial College London / Takedo International, UK; J Polak, Imperial College London, UK
An innovative new theoretical application framework is presented for evaluating individual and household space-time accessibility, integrating activity, group decision making, space-time geography and econometric theories within a holistic framework.
Space-time accessibility measures are amongst the most powerful and conceptually attractive accessibility measures in existence. Encompassing a number of the multiple dimensions of accessibility, space-time accessibility measures have applications in the areas as diverse as activity/travel behaviour analysis, travel/activity planning, user benefit/consumer welfare analyses, accessibility planning, social, equity and liveability assessments, performance measurement and activity based modelling amongst others.
However despite a number of recent advances in the assessment of space-time accessibility, existing space-time measures neglect a number of important considerations. Space-time accessibility measures have historically tended to neglect consideration of the nature and effect of group decision making on the scheduling of activities and the overall accessibility of groups such as households or firms and the interactive influences of the group decision making processes on the activity/travel behaviour and accessibility of the individuals comprising these groups.
In this paper we present a theoretical framework which extends existing activity based space-time locational and route benefit measures, previously developed by the authors, in two important respects. The first extension is to encompass income and cost considerations, such as the cost of goods, services and travel, in addition to the income derived from activity participation, an important but hitherto neglected element in space-time accessibility. The second extension presented is to extend the family of cost based space-time user benefit and related space-time utility accessibility measures from a primary focus on the individual to encompass multiple individuals interacting within households or firms. The resulting household space-time user benefit and space-time accessibility measures are shown to encapsulate participation in joint and shared activities by household members, and have until now been largely neglected in traditional studies of space-time accessibility.
The paper outlines how recent developments in space-time geography measurement theory can be utilised to identify the necessary spatial-temporal conditions for joint and shared activity participation between two or more household members and subsequently outlines how the proposed family of accessibility measures can be applied to physical and virtual interactions amongst individuals and household members.
We proceed to demonstrate the applicability of the new theoretical and application framework by using a household travel diary dataset previously collated for a major European urban conurbation, to identify a number of distinct household structures, corresponding family of individual and household activity schedules, and utilise stochastic frontier models to identify the temporal location of individual space-time prism vertices and subsequently proceed to estimate model parameters for the underlying individual and household space-time accessibility measures. Several hypothetical applications of the framework are presented utilising; real world household structures; associated individual activity schedules and temporal constraints; a detailed spatially referenced multi-modal transportation network and land use/service network, implemented through a bespoke spatially based decision support software tool developed specifically to support efficient and practical implementation of the framework.
The hypothetical case study application reveals a number of interesting findings most notable being; the impact that different types of household decision making processes have on the individual activity-travel behaviour and on the space-time accessibility of each individual member of the household as well as on the household?s overall space-time accessibility and how these inter-relationships vary spatially over the urban conurbation.
The paper concludes by outlining the strengths, areas for improvement and further research associated with the new theoretical and application framework.
Association for European Transport