Flowstrates: An Approach for Visual Exploration of Temporal Origin‐Destination Data

Many origin‐destination datasets have become available in the recent years, e.g. flows of people, animals, money, material, or network traffic between pairs of locations, but appropriate techniques for their exploration still have to be developed. Especially, supporting the analysis of datasets with a temporal dimension remains a significant challenge. Many techniques for the exploration of spatio‐temporal data have been developed, but they prove to be only of limited use when applied to temporal origin‐destination datasets. We present Flowstrates , a new interactive visualization approach in which the origins and the destinations of the flows are displayed in two separate maps, and the changes over time of the flow magnitudes are represented in a separate heatmap view in the middle. This allows the users to perform spatial visual queries, focusing on different regions of interest for the origins and destinations, and to analyze the changes over time provided with the means of flow ordering, filtering and aggregation in the heatmap. In this paper, we discuss the challenges associated with the visualization of temporal origin‐destination data, introduce our solution, and present several usage scenarios showing how the tool we have developed supports them.     

The Electric Vehicle Shortest-Walk Problem With Battery Exchanges

Electric vehicles (EV) have received much attention in the last few years. Still, they have neither been widely accepted by commuters nor by organizations with service fleets. It is predominately the lack of recharging infrastructure that is inhibiting a wide-scale adoption of EVs. The problem of using EVs is especially apparent in long trips, or inter-city trips. Range anxiety, when the driver is concerned that the vehicle will run out of charge before reaching the destination, is a major hindrance for the market penetration of EVs. To develop a recharging infrastructure it is important to route vehicles from origins to destinations with minimum detouring when battery recharging/exchange facilities are few and far between. This paper defines the EV shortest-walk problem to determine the route from a starting point to a destination with minimum detouring; this route may include cycles for detouring to recharge batteries. Two problem scenarios are studied: one is the problem of traveling from an origin to a destination to minimize the travel distance when any number of battery recharge/exchange stops may be made. The other is to travel from origin to destination when a maximum number of stops is specified. It is shown that both of these problems are polynomially solvable and solution algorithms are provided. This paper also presents another new problem of finding the route that minimizes the maximum anxiety induced by the route.     

Optimal facility location with random throughput costs

In this paper we consider the optimal location and size of facilities where the throughput costs for each facility are random. Given a set of origins and a set of destinations, we want to determine the optimal location and size of a set of intermediate facilities in order to minimize the expected total generalized transportation cost. The generalized transportation cost of a freight unit from an origin to a destination passing through a facility is the sum of two terms: the transportation cost from the origin to the destination through the facility and the throughput cost of the facility. While the first term is deterministic, the second one is stochastic with a Gumbel probability distribution. Looking for the expected value of the optimal solution, a mixed deterministic nonlinear problem for the optimal location of the facilities is derived. Two heuristics, which give very good approximations to the optimum, are proposed.     

Access to urban parks: Comparing spatial accessibility measures using three GIS-based approaches

Urban parks are essential components of urban ecosystems, providing recreation and relaxation places to residents. Measuring the spatial accessibility to urban parks serves as an initial step in urban planning and developing urban development strategies to improve social and environmental justice. This study aims to evaluate measures of spatial accessibility to urban parks by comparing three geographic information systems (GIS)-based approaches, accounting for network complexity, transport modes, distance thresholds, and destination choices. Taking Ipswich City (Australia) and Enschede (the Netherlands) as two testbeds, we examine the spatial patterns of a total of 21 accessibility measures in the two cities and conduct a correlation and principal component analysis to unravel the interrelationship between these measures. The results suggest that among all measures under the three approaches, the selection of distance thresholds and transport modes matter more to accessibility measures than the destination choices. Furthermore, when distance threshold and transport mode are held constant, the network-based and entrance-based methods provide more realistic accessibility measures than other methods. We also discuss the generality of the entrance-based method we propose and suggest ways to choose the most appropriate accessibility measure for use in different contexts.     

Network-based Accessibility Measures for Vulnerability Analysis of Degradable Transportation Networks

Accessibility is a fundamental concept in transportation analysis and urban planning. Typically, accessibility refers to the ‘ease’ of reaching opportunities for activities and services and can be used to assess the performance of a transportation and urban system. In this paper, we present network-based accessibility measures for assessing vulnerability of degradable transportation networks. The network-based accessibility measures consider the consequence of one or more link failures in terms of network travel time or generalized travel cost increase as well as the behavioral responses of users due to the failure in the network. To model different dimensions of travel behavioral responses, a combined travel demand model is adopted to estimate the long-term equilibrium network condition due to network disruptions. Numerical examples are conducted to demonstrate the feasibility of the proposed vulnerability measures for assessing degradable transportation networks. The results indicate that the accessibility measures derived from the combined travel demand model are capable of measuring the consequences of both demand and supply changes in the network and have the flexibility to reflect the effects of different travel choice dimensions on the network vulnerability.     

Public transport accessibility measure based on weighted door to door travel time

Providing accessibility by public transportation is one of the main concerns in sustainable transportation development. An appropriate accessibility index should not only take transportation and land use into account but also the people who want to attend activities via the transport system. Travel time as the most common variable is used to indicate the role of transportation. A trip with public transport includes different parts: walking from the origin point to the bus stop or from the bus stop to the destination point, waiting for the bus to arrive, and in-vehicle time. These different parts have different weight values for passengers which affect their tendency towards traveling by public transportation. In this paper, a GIS-based multimodal gravity model is developed based on the weighted door to door travel time to compute accessibility by public transportation. Five main distinct urban activities including employment, education, healthcare, shop, recreation opportunities, and services are considered and the accessibility of the target population at the census block level to these destinations through public transportation is computed. In the next step, in order to consider all activities together and report a single unique index, the five computed accessibility indices are integrated into a composite index using a principal component analysis (PCA). The integrated accessibility measure helps to get an insight into the relative distribution of the benefits of public transportation and its interaction with the land use. The proposed method is applied to the City of Isfahan in Iran. The results indicate where places, for each activity and in overall, would benefit from the better land use and public transportation interaction and where regions would suffer from low accessibility level. This work provides a methodological framework as a tool for measuring the performance of public transportation and its interaction with the land use pattern.     

Multi-route railroad blocking problem by improved model and ant colony algorithm in real world

In rail freight transportation, general merchandise freight cars may pass through many classification stations on their route from origin to destination. The Railroad Blocking Problem (RBP) is to reclassify inbound traffic from various origins in the classification stations and put them on outbound trains with the same or close destinations, the objective of the RBP is to minimize the total operating costs of delivering all traffic on the railway network while satisfying the resource and capacity constraints at the stations and the priority constraints for shipments. In this paper, we introduce a new mathematic model which can comprehensively describe the blocking strategy and various combinations of multi-route O–D pairs in large scale railway network. Furthermore, we propose an improved Ant Colony (AC) algorithm for RPB, and a computational experiment derived from the real life instances of coal heavy haul rail network in north China is given. Experimental results verified the validation of the model and effectiveness of the algorithm.     

Where were you? Development of a time-geographic approach for activity destination re-construction

With the use of individual-level travel survey datasets describing the detailed activities of households, it is possible to analyze human movements with a high degree of precision. However, travel survey data are not without quality issues. Potential exists for origins and destinations of reported trips not to be geo-referenced, perhaps due to misreported information or inconsistencies in spatial address databases, which can limit the usefulness of the survey data. From an analytical standpoint, this is a serious problem because a single unreferenced stop in a trip record in effect renders that individual’s data useless, especially in cases where analyzing chains of activity locations is of interest. This paper presents a framework and basic computational approach for exploring unlocatable activity locations inherent to travel surveys. Derived from recent work in developing a network-based, probabilistic time geography, the proposed methods are able to estimate the likely locations of missing trip origins and destinations. The methods generate probabilistic potential path trees which are used to visualize and quantify potential locations for the unreferenced destinations. The methods are demonstrated with simulated survey data from a smaller metropolitan area.     

Learning beyond books—strategies for ambient media to improve libraries and collaboration spaces as interfaces for social learning

With the advent of digital media and online information resources, public libraries as physical destinations for information access are being increasingly challenged. As a response, many libraries follow the trend of removing bookshelves in order to provide more floorspace for social interaction and collaboration. Such spaces follow a Commons 2.0 model: they are designed to support collaborative work and social learning. The acquisition of skills and knowledge is facilitated as a result of being surrounded by and interacting with a community of likeminded others. Based on the results of a case study on a Commons 2.0 library space, this paper describes several issues of collaboration and social learning in public library settings. Acknowledging the significance of the architectural characteristics of the physical space, we discuss opportunities for ambient media to better reflect the social attributes of the library as a place; i.e. amplify the sense of other co-present library visitors and provide opportunities for shared encounters and conversations, which would remain invisible otherwise. We present the design of a user check-in system for improving the library as a physical destination for social learning, sharing, and inspiration for and by the community.     

Su una estensione di un particolare modello (non lineare) per trasporti interni industriali

Recently, by using the method of dynamic programming, M. Volpato determined a policy of minimized costs to supply many destinations from a single source, the transport costs being functions (linear or not linear) which satisfy only the condition of inferior semi-continuity. Among the feasible policies he admitted also the indireact shipping from source to destination (i.e. a policy, where a larger quantity than required is sent to certain destination, and the surplus is delivered to a destination which follows it in a given order). In this paper the problem is studied for the case in which there is more than one source, and the availability of every source is limited. In this case it is possible to consider the problem as a multi-stage process, and to solve again it by the method of dynamic programming.

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Lavoro eseguito nell'ambito del Gruppo di ricerca matematica n. 38 (Ca' Foscari, Venezia) del C.N.R. per l'anno accademico 1964–65.     

Travel times and transfers in public transport: Comprehensive accessibility analysis based on Pareto-optimal journeys

Efficient public transport (PT) networks are vital for well-functioning and sustainable cities. Compared to other modes of transport, PT networks feature inherent systemic complexity due to their schedule-dependence and network organization. Because of this, efficient PT network planning and management calls for advanced modeling and analysis tools. These tools have to take into account how people use PT networks, including factors such as demand, accessibility, trip planning and navigability. From the PT user perspective, the common criteria for planning trips include waiting times to departure, journey durations, and the number of required transfers. However, waiting times and transfers have typically been neglected in PT accessibility studies and related decision-support tools. Here, we tackle this issue by introducing a decision-support framework for PT planners and managers, based on temporal networks methodology. This framework allows for computing pre-journey waiting times, journey durations, and number of required transfers for all Pareto-optimal journeys between any origin–destination pair, at all points in time. We visualize this information as a temporal distance profile, covering any given time interval. Based on such profiles, we define the best-case, mean, and worst-case measures for PT travel time and number of required PT vehicle boardings, and demonstrate their practical utility to PT planning through a series of accessibility case studies. By visualizing the computed measures on a map and studying their relationships by performing an all-to-all analysis between 7463 PT stops in the Helsinki metropolitan region, we show that each of the measures provides a different perspective on accessibility. To pave the way towards more comprehensive understanding of PT accessibility, we provide our methods and full analysis pipeline as free and open source software.     

Formulating and solving splittable capacitated multiple allocation hub location problems

It is only recently that good formulations and properties for the basic versions of the hub location problem have become available. Now, versions closer to reality can be tackled with greater guarantees of success. This article deals with the case in which the capacity of the hubs is limited. The focus is on the following interpretation of this capacity: there is, for each hub, an upper bound on the total flow coming directly from the origins. Our problem has the so-called multiple allocation possibility, i.e., there is no hub associated to each node; on the contrary, flows with, say, the same origin but different destinations, can be sent through different routes. Moreover, it is assumed that the flow between a given origin–destination pair can be split into several routes; if this is not the case, the problem becomes quite different and cannot be approached by means of the techniques used in this paper.Tight integer linear programming formulations for the problem are presented, along with some useful properties of the optimal solutions which can be used to speed up the resolution.The computational experience shows that instances of medium size can be solved very efficiently using the new method, which outperforms other methods given in the literature.     

The Role of Transport and Population Components in Change in Accessibility: the Influence of the Distance Decay Parameter

Investment in transport infrastructure is the main factor responsible for decreasing origin-destination travel times, which are then implemented into a potential accessibility measure. This measure uses population size as a proxy for a destination’s attractiveness. Thus, changes in population distribution as well as the development of the transport infrastructure are mutually responsible for changes in accessibility. The potential accessibility measure is applied to assess change in accessibility in Poland over a twenty year period of time (1995–2015). During this time Poland has experienced a significant change in population distribution. At the same time, accession to the European Union provided an opportunity to use the structural funds and has resulted in an unprecedented development of the transport infrastructure, in particular the road network. The coexistence of both phenomena provides perfect conditions to investigate the complex interrelationship of both components of accessibility, namely transport and land-use. This leads towards a change in the level of accessibility and its spatial pattern, resulting in a transformation of the level of territorial cohesion. However, the selection of the particular impedance parameters greatly influences the importance assigned to an element of infrastructure or a component of population accessibility. Thus, several impedance functions are applied in order to capture their influence on the balance between the infrastructure and population components of accessibility change.     

Unicast-based fault-tolerant multicasting in wormhole-routed hypercubes

A unicast-based fault-tolerant multicasting method is proposed for hypercubes, which can still work well when the system contains enough faults. A multicast message may be unable to reach a destination if Hamming distance between the destination and the multicast source is large enough. A multicast message fails if any one of the destinations is unreachable from the source. An effective destination ordering scheme of the destinations is proposed for one-port systems first, it is extended to all-port systems for unicast-based fault-tolerant multicasting. Unreachable destinations from the source based on the local safety information are forwarded to a reachable destination, where the multicast message can be routed reliably. Destination ordering is completed based on Hamming distance. A multiple round p-cube routing scheme is presented for a deadlock-free fault-tolerant routing for each unicast step in hypercubes, where the same virtual channel is used for each round of p-cube routing. Sufficient simulation results are presented by comparing with the previous methods.     

A prototype store choice and location modelling system using Dempster–Shafer theory

This paper concerns the study of destination choice modelling, more specifically identifying within some area (e.g. a city) the region where a particular store is the most favourable to be visited by individuals. An influence measure is constructed for each individual, which incorporates the modern technique known as Dempster–Shafer theory. Based on the evidence of the shopping destinations of individuals, geographical regions are found for levels of largest belief and plausibility (within Dempster–Shafer theory) for specific stores being the most favourable to visit. Additionally, this method may be used to identify the possible position of new stores, based on regions of most uncertainty or conflict in store choice. A prototype choice modelling system is introduced to enable the series of associated results to be easily visualized and analysed.     

Accessibility and Network Structures in the German Commuting

A great deal of attention has recently been paid to the analysis of the structure and evolution of (complex) networks, starting from pioneering contributions in the physical and social sciences—and more recently in the regional and transportation sciences—mainly concerning the relevance of highly connected nodes (hubs). The presence of hubs identifies a network as Scale-Free (SF), because of its intrinsic characteristic of exhibiting power-law distributions in its connectivity structure, and thus highly heterogeneous patterns. The focus of this paper is to explore the homogeneous vs. heterogeneous characteristics of the German commuting network, by focusing on the role of accessibility. The concept of accessibility has a long tradition in the transport economics literature, starting with the fundamental works by Hansen in the 1950’s and later on by Weibull in the 1980’s. These authors defined accessibility as the potential of opportunities for spatial interaction. Accessibility conceived in this manner should also capture spatial structure effects and thus the network configuration properties, such as connectivity. This conventional accessibility function—in the light of the related economic activities—is be used as a suitable instrument to identify the major German hub/attraction nodes. As the functional form in this potential accessibility, the power-decay function will be considered—in addition to the negative exponential function—in order to explore the spatial configuration patterns, i.e. whether people perceive commuting cost in log-like way. The connectivity network analysis will then be developed as a benchmark to testing the results emerging from the spatial-economic analysis. In our application we consider home-to-work commuters travelling between 439 German districts, for the year 2002. The final results seem to highlight the tendency, in Germany, towards a multi-nodality network, where accessibility can play a fundamental role.     

Modeling interregional commodity flows with incorporating network autocorrelation in spatial interaction models: An application of the US interstate commodity flows

Spatial interaction models are frequently used to predict and explain interregional commodity flows. Studies suggest that the effects of spatial structure significantly influence spatial interaction models, often resulting in model misspecification. Competing destinations and intervening opportunities have been used to mitigate this issue. Some recent studies also show that the effects of spatial structure can be successfully modeled by incorporating network autocorrelation among flow data. The purpose of this paper is to investigate the existence of network autocorrelation among commodity origin–destination flow data and its effect on model estimation in spatial interaction models. This approach is demonstrated using commodity origin–destination flow data for 111 regions of the United States from the 2002 Commodity Flow Survey. The results empirically show how network autocorrelation affects modeling interregional flows and can be successfully captured in spatial autoregressive model specifications.     

Web popularity: an illusory perception of a qualitative order in information

Using a psychotechnological perspective, this study discusses the current model of information ranking by search engines, based on quantitative Web Popularity (WP), which binds users to a cognitive adaptation to the rank-system restrictions. This phenomenon gives rise to a “rich-get-richer” effect on the Web. This paper claims that such an effect could be limited or reversed by the introduction of quality factors in ranking, and addresses the case of accessibility as a fundamental such factor. A study is reported which, through introducing an accessibility factor in a well-known popularity ranking algorithm, demonstrates that this transformation allows a qualitative rearrangement, without modifying or weighing on the properties of the rank. The overall approach is grounded on two development factors: the analysis of accessibility through specific tools and the employment of this analysis within all components used to build up the ranking. The results show that it is important to reconsider WP as including not only on the number of inbound and outbound links of a website, but also on its level of accessibility for all users, and on users’ judgment of the website use as efficient, effective, and satisfactory.     

Models and solution methods for the uncapacitated r‐allocation p‐hub equitable center problem

Hub networks are commonly used in telecommunications and logistics to connect origins to destinations in situations where a direct connection between each origin–destination (o‐d) pair is impractical or too costly. Hubs serve as switching points to consolidate and route traffic in order to realize economies of scale. The main decisions associated with hub‐network problems include (1) determining the number of hubs (p), (2) selecting the p‐nodes in the network that will serve as hubs, (3) allocating non‐hub nodes (terminals) to up to r‐hubs, and (4) routing the pairwise o‐d traffic. Typically, hub location problems include all four decisions while hub allocation problems assume that the value of p is given. In the hub median problem, the objective is to minimize total cost, while in the hub center problem the objective is to minimize the maximum cost between origin–destination pairs. We study the uncapacitated (i.e., links with unlimited capacity) r‐allocation p‐hub equitable center problem (with) and explore alternative models and solution procedures.