Integrating people and place: A density-based measure for assessing accessibility to opportunities
28 Jul 2014-Journal of Transport and Land Use (Journal of Transport and Land Use)-Vol. 7, Iss: 2, pp 23-40
TL;DR: The goal here is to understand the magnitude and nature of the opportunities a mobile object had access to, given known location points and a time budget for its movement.
Abstract: Mobile object analysis is a well-studied area of transportation and geographic information science (GIScience). Mobile objects may include people, animals, or vehicles. Time geography remains a key theoretical framework for understanding mobile objects' movement possibilities. Recent efforts have sought to develop probabilistic methods of time geography by exploring questions of data uncertainty, spatial representation, and other limitations of classical approaches. Along these lines, work has blended time geography and kernel density estimation in order to delineate the probable locations of mobile objects in both continuous and discrete network space. This suite of techniques is known as time geographic density estimation (TGDE). The present paper explores a new direction for TGDE, namely the creation of a density-based accessibility measure for assessing mobile objects' potential for interacting with opportunity locations. As accessibility measures have also garnered widespread attention in the literature, the goal here is to understand the magnitude and nature of the opportunities a mobile object had access to, given known location points and a time budget for its movement. New accessibility measures are formulated and demonstrated with synthetic trip diary data. The implications of the new measures are discussed in the context of people-based vs. placed-based accessibility analyses.
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TL;DR: Results show that individual and place-based differences in food accessibility may be delineated with the metrics, and possible ‘deserts’ or areas of inaccessibility may be identified through a bottom-up analysis of the travel and mobility experience of a representative sample of individuals.
72 citations
TL;DR: In this paper, the authors investigated the accessibility of the older population to potential activities in a smaller metropolitan area in the state of Florida, using highly disaggregate spatial data containing the locations of populations and possible activities, and implemented accessibility models in a Geographic Information Systems (GIS) environment.
Abstract: Accessibility is facilitated by well-organized transportation systems that move people efficiently, and it is improved as more activities are reachable to people given the means of available travel. As the current population ages, it will ultimately challenge those who manage transportation systems in their attempts to satisfy the older population’s basic needs. Scanning the literature, accessibility has not been fully explored in relation to aging and older populations. We construct a systematic quantitative analysis of the older population’s accessibility to potential activities. Given their residential patterns and the prevailing transportation system, we ask whether they have as much potential accessibility to activities as their younger counterparts. Our study area is a smaller metropolitan area in the state of Florida. Using highly disaggregate spatial data containing the locations of populations and possible activities, we implement accessibility models in a Geographic Information Systems (GIS) environment, accounting for mode of transportation. Scenarios and activities analyzed are informed by a review of the broader literature as well as our own analysis of the 2009 National Household Travel Survey. We find that the potential accessibility of the aging population varies by activity type and differs with other age group cohorts. When we look in detail at subgroups within the aging population, the oldest group (those 85+) tends to have higher levels of accessibility.
61 citations
TL;DR: In this article, the authors highlight the impact of addressing competition for different urban services in the cumulative opportunities measure and show that considering competition changes the spatial patterns of accessibility and its equity.
51 citations
TL;DR: In this paper, the authors examined six income groups in the Los Angeles metropolitan area and found that job accessibility affects the employment status of medium-to-low income groups (household income between US$25,000 and US$75,000).
Abstract: Improving job accessibility can increase the probability for individual persons to be employed and reduce their commutes. Empirical research suggests that the relationship between job accessibility and employment outcomes differ across income groups, but no research has investigated the difference or explored which income groups benefit the most from job accessibility improvements. This research fills the gap by examining six income groups in the Los Angeles metropolitan area. Results show that job accessibility affects the employment status of medium-to-low income groups (household income between US$25,000 and US$75,000). For the lowest-income group (household income lower than US$25,000), owning a car significantly improves their chances to be employed, but job accessibility has no effect. On the other hand, higher job accessibility is associated with shorter commuting distance for the other five income groups, but not for the lowest-income group. These results suggest that transportation and land use policies need to address the specific needs of distinct population groups and underscore the importance of spatial access for the middle-class, which tends to be overlooked in the literature on transportation equity.
44 citations
TL;DR: The results of the case study show that the proposed location-based space-time accessibility measures can well capture the temporal variation of accessibility, due to the dynamics both of traffic conditions and of individuals' intensities in performing activities at different times of day.
41 citations
References
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TL;DR: The potential path area is used, which is the projection of a space–time prism onto a plane, to determine an individual’s destination choice set given their spatio-temporal constraints, and this set is a more realistic representation of the shopping alternatives available to the individual.
76 citations
TL;DR: This paper starts with the standard assumption of time geography (no further knowledge), and develops the appropriate probability distribution by three equivalent approaches.
Abstract: Time geography uses space---time volumes to represent the possible locations of a mobile agent over time in a x---y---t space A volume is a qualitative representation of the fact that the agent is at a particular time t i inside of the volume's base at t i Space---time volumes enable qualitative analysis such as potential encounters between agents In this paper the qualitative statements of time geography will be quantified For this purpose an agent's possible locations are modeled from a stochastic perspective It is shown that probability is not equally distributed in a space---time volume, ie, a quantitative analysis cannot be based simply on proportions of intersections The actual probability distribution depends on the degree of a priori knowledge about the agent's behavior This paper starts with the standard assumption of time geography (no further knowledge), and develops the appropriate probability distribution by three equivalent approaches With such a model any analysis of the location of an agent, or relations between the locations of two agents, can be improved in expressiveness as well as accuracy
70 citations
TL;DR: In this paper, the authors used a dataset from the U.S. Census known as Longitudinal Employer-Household Dynamics (LEHD) to explore temporal commuting-land-use relationships.
64 citations
TL;DR: In this article, the authors evaluated the effects of the I-35W bridge collapse on road-users in the Minneapolis-St Paul, Minnesota Twin Cities metropolitan area and concluded that the failure of the bridge resulted in an economic loss of US$71,000 to US$220,000 a day, depending on how flexible road users in the system adjusted their trip destinations in response to the bridge closing.
Abstract: This study evaluates the effects of the I-35W bridge collapse on road-users in the Minneapolis-St Paul, Minnesota Twin Cities metropolitan area. We adopted the Twin Cities Seven-County travel demand model developed in previous research, re-calibrated it against July 2007 loop detector traffic data, and used this model to carry out an evaluation of economic loss incurred by increased travel delay in alternative scenarios before and after the bridge collapse. We conclude that the failure of the I-35W bridge resulted in an economic loss of US$71,000 to US$220,000 a day, depending on how flexible road-users in the system adjusted their trip destinations in response to the bridge closing. We also estimate that the major traffic restoration projects Minnesota Department of Transportation has implemented in quick response to the bridge collapse can save road-users US$9500–17,500 a day. This translates into a benefit–cost ratio of 2.0–9.0, suggesting these projects are highly beneficial in an economic sense. In t...
63 citations
14 Sep 2010
TL;DR: The main advantages of this time-geographic method of density estimation for moving point objects are that positive intensities are only assigned to locations within a moving object's potential path area and that it avoids arbitrary parameter selection as the amount of smoothing is controlled by the object's maximum potential velocity.
Abstract: This research presents a time-geographic method of density estimation for moving point objects. The approach integrates traditional kernel density estimation (KDE) with techniques of time geography to generate a continuous intensity surface that characterises the spatial distribution of a moving object over a fixed time frame. This task is accomplished by computing density estimates as a function of a geo-ellipse generated for each consecutive pair of control points in the object's space-time path and summing those values at each location in a manner similar to KDE. The main advantages of this approach are: (1) that positive intensities are only assigned to locations within a moving object's potential path area and (2) that it avoids arbitrary parameter selection as the amount of smoothing is controlled by the object's maximum potential velocity. The time-geographic density estimation technique is illustrated with a sample dataset, and a discussion of limitations and future work is provided.
60 citations
"Integrating people and place: A den..." refers background or methods in this paper
...Downs (2010) fused time geography and kernel density estimation by developing time-geographic density estimation (TGDE), a technique that may be used to estimate mobile objects’ probable locations in continuous space given a time budget between known control points (Downs 2010)....
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...…with this thrust, Downs (2010) fused time geography and kernel density estimation by developing time-geographic density estimation (TGDE), a technique that may be used to estimate mobile objects’ probable locations in continuous space given a time budget between known control points (Downs 2010)....
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...In Euclidean space, the space-time path is generated by connecting consecutive locations with straight lines; in network space, it is modeled by connecting them with shortest paths along the network (Downs 2010)....
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...Consistent with this thrust, Downs (2010) fused time geography and kernel density estimation by developing time-geographic density estimation (TGDE), a technique that may be used to estimate mobile objects’ probable locations in continuous space given a time budget between known control points…...
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...For a fuller accounting on the basic motivations and aims of TGDE, readers are referred to Downs (2010), Downs and Horner (2012), and Horner et al. (2012) for additional discussion of possible parameterizations of PPT* and the factor sij....
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