Study of the topology and robustness of airline route networks from the complex network approach: a survey and research agenda

Communication via air routes is an important issue in a world organized around a web city network. In this context, the robustness of network infrastructures, e.g. air transport networks, are a central issue in transport geography. Disruption of communication links by intentional causes (e.g., terrorist attack on an airport) or unintentional (e.g., weather inclemency) could be crucial for countries, regions and even the airlines affected themselves. Policymakers and the management of airlines and alliances should be able to reduce the effects of such interruptions in order to ensure good communication through air transport (i.e., maximize the robustness of their network at a reasonable cost). The literature review of the study of air transport route networks through an analysis of complex networks has highlighted a lack of contributions to the study of the topology and the robustness of such networks which contrasts, with advances undertaken for other transport networks or communication systems. This survey suggests areas in which research should be undertaken, based on the existing literature in other areas and from three different perspectives: global route networks, airline alliances, airlines and airports so as to help towards a better understanding of air traffic and, therefore, to be able to assess the potential damage of any airport being inoperative for a continent, country or airline.     

综合维修天窗与列车开行方案的协同优化研究

在提速后的铁路繁忙干线上,旅客列车开行方案比较复杂,需要兼顾包括天窗设置在内的多方面因素.在区段内考虑综合维修天窗与旅客列车的协调主要是优化两者之间的时间关系.运用同余思想分析旅客列车的合理开车范围.通过建立维修天窗与列车开行方案之间的协调优化关系模型,得出理论上的最佳天窗时段就是使概率频数最小的列车合理开车时间段.     

基于满意度分析的高速铁路列车运行调整优化研究

为了研究高速铁路列车在恶劣天气影响下导致区段临时限速情景下的列车运行调整问题,文中选择总晚点时间和晚点列数2个指标,分别转化为列车延误满意度和正点率满意度,建立线性满意度、梯形满意度和传统多目标线性加权模型,通过改变列车到发时刻、运行径路、次序等实现高效、准点的列车运行调整。最后设计一个限速场景,运用软件求解,通过改变总晚点时间和晚点列数的权重,得到模型的帕累托解,结果表明满意度模型的帕累托解优于线性加权模型。此外,算例验证了梯形满意度线性加权模型从计算时间上优于传统多目标线性加权模型,提出的满意优化模型可以辅助调度员在发布限速命令后尽快获得满意的调度方案。     

基于连通可靠性的车辆路径问题

物流配送车辆路径问题(VRP)是一个NP-hard问题,很多求解方法仅考虑路网连通无穷大的情况,将其看成平均旅行时间问题,对于突发事件下造成路网拥堵情况下的车辆路径问题很少涉及,对此结合蚁群算法,对突发事件下各路段的连通可靠性进行比较后选择合适路段通过,用以提高路网的通行能力。     

The impact of hubbing concentration on flight delays within airline networks: An empirical analysis of the US domestic market

This paper explores the relationship between hubbing activities and flight delays in the United States from an airline-specific network perspective. Airline hubbing is measured with the Hubbing Concentration Index. We estimate the impact of hubbing behavior on delays, using three measures of delay, two based on delay against schedule, and the third based on buffer-corrected excess travel times. A significant (and positive) influence of hubbing concentration can only be found for the latter delay indicator. We conclude that airlines use buffer times to mitigate passenger-perceived delays against schedule that would, without buffers, arise from more complex network operations.     

Towards collaborative, intermodal hub networks: A case study in the fast moving consumer goods market

Collaborative hub networks can provide an answer to the need to decrease logistics cost and maintain logistics service levels by shifting consolidated flows to modes that are better suited for handling large volumes (rail, barge, coastal shipping), so economies of scale can be obtained. This necessity has been increased by the tendency of globalization of industries, smaller shipments sizes, high frequencies, and the fragmentation of flows. Through collaboration the necessary synchronization between expensive but fast and flexible means of transport and inexpensive, but slow and inflexible means can be combined in an intermodal hub network. This paper shows the rationale behind these collaborative hub networks, based on the literature on the design of many-to-many hub networks. The resulting methodology is explained through presenting the results of the design and implementation of collaborative hub network for the distribution of fast moving consumer goods using a combination of trucking and inland barges. This concept, first proposed by Vermunt [Vermunt, A.J.M., 1999. Multilognet, the intelligent multimodal logistics network, an important node in the worldwide logistics net, Vermunt Logistiek Advies v.o.f., working paper (in Dutch)], won the European Intermodal Award of the European Intermodal Association in 2003, and after extensive research was launched in The Netherlands as a commercial pilot by logistics service provider Vos Logistics and barge operator Riverhopper in January 2004.     

Explaining changes and trends in the airline industry: Economies of density,multiproduct scale,and spatial scope

Changes in the shape and size of airline networks have not been explained clearly from a cost perspective based on the finding of increasing returns to density for given route structures and constant returns to scale for variable network size. We reassessed the estimates of these economies by using new scale and scope indices, finding savings due to changes in route structures and various types of economies of spatial scope not previously calculated: network size, trunk-local services and domestic-international services. Results contribute new insights on the role of cost incentives in the observed changes and trends in the airline industry.     

Optimal inter-area coordination of train rescheduling decisions

Railway dispatchers reschedule trains in real-time in order to limit the propagation of disturbances and to regulate traffic in their respective dispatching areas by minimizing the deviation from the off-line timetable. However, the decisions taken in one area may influence the quality and even the feasibility of train schedules in the other areas. Regional control centers coordinate the dispatchers’ work for multiple areas in order to regulate traffic at the global level and to avoid situations of global infeasibility. Differently from the dispatcher problem, the coordination activity of regional control centers is still underinvestigated, even if this activity is a key factor for effective traffic management.This paper studies the problem of coordinating several dispatchers with the objective of driving their behavior towards globally optimal solutions. With our model, a coordinator may impose constraints at the border of each dispatching area. Each dispatcher must then schedule trains in its area by producing a locally feasible solution compliant with the border constraints imposed by the coordinator. The problem faced by the coordinator is therefore a bilevel programming problem in which the variables controlled by the coordinator are the border constraints. We demonstrate that the coordinator problem can be solved to optimality with a branch and bound procedure. The coordination algorithm has been tested on a large real railway network in the Netherlands with busy traffic conditions. Our experimental results show that a proven optimal solution is frequently found for various network divisions within computation times compatible with real-time operations.     

Vulnerability assessment and re-routing of freight trains under disruptions: A coal supply chain network application

In this paper, we present a two-stage mixed integer programming (MIP) interdiction model in which an interdictor chooses a limited amount of elements to attack first on a given network, and then an operator dispatches trains through the residual network. Our MIP model explicitly incorporates discrete unit flows of trains on the rail network with time-variant capacities. A real coal rail transportation network is used in order to generate scenarios to provide tactical and operational level vulnerability assessment analysis including rerouting decisions, travel and delay costs analysis, and the frequency of interdictions of facilities for the dynamic rail system.     

Route churn: an analysis of low-cost carrier route continuity in Europe

Discontinuity of air routes is a subject that has been analysed in various ways. For example, the complex network approach focuses on network robustness and resilience due to route interruptions during a relatively short period. Also seasonal interruptions of air routes are a well-documented phenomenon in the context of demand variability. However, only recently discussions emerge on the more permanent cessation of air routes, the route churn. Today, European low-cost carriers frequently apply route churn in their networks. To enable early route churn detection in these networks, a regression model is developed in which route characteristics explain the churning likelihood of individual routes. The results of the econometric analysis show that churn rates are higher during an economic downturn, within the Eastern European market, between the Eastern and the Mediterranean market and between primary airports. In addition, we find that distance and the number of seats offered have a significant negative effect on the churn likelihood. The results also show significant effects of market share, seasonality and route age on the chance of cessation. To conclude, the paper demonstrates substantial differences in churn behaviour amongst specific low-cost carriers.     

Characterization of delay propagation in the air traffic network

We build a delay propagation network based on Bayesian Network approach to study the complex phenomenon of delay propagation within a large network consisting of the 100 busiest airports in the United States. Through topological analysis and probability analysis, we investigate the characterization of delay propagation among airports and the impact of different types of airports on delay propagation. Results indicate that the cumulative degree distribution of the delay propagation network follows an exponential function and flight delays take at most one transhipment to go from each airport to any other airports on average. For each individual airport, the effects of delay propagation are associated with airports size (traffic flow), small airports are easily affected by other airports while large airports are more affecting downstream airports but fewer affected by upstream airports. Finally, we show how the number of affected airports changes as a function of the delayed airports based on different simulation strategies.     

Real-time mobilization decisions for multi-priority emergency response resources and evacuation groups: Model formulation and solution

This paper presents a model formulation and solution for simultaneous mobilization destination, traffic assignment, and departure schedule for multi-priority groups (SMDTS-MPG) for real-time emergency response in no-notice disasters. The presented approach addresses the decision context in which multiple emergency responses and evacuation flow groups with different destinations and varying priorities coexist in the same traffic network, within which simultaneous mobilization strategies must consider this requirement. The proposed modeling technique and the cell transmission model (CTM)-based linear-programming model provides a mechanism to accomplish this goal in an intuitive and coherent manner. The proposed matrix formulation of the SMDTS-MPG model permits the rapid deployment of the model to large networks. Model formulation and numerical examples are presented in detail in this paper.     

A model for taxi pooling with stochastic vehicle travel times

Taxi pooling means the sharing of a taxi by more than one passenger with at least a semi-common route. Currently, a trial-and-error process is adopted, taking into account expected travel times, for taxi pooling, a method which is neither effective nor efficient. This is because stochastic disturbances arising from variations in the taxi travel times that occur in actual traveling are neglected. In the worst case scenario, where vehicle travel times fluctuate wildly during operations, the planned schedule can be disturbed enough to lose its optimality. Therefore, in this study, a network flow technique is used to construct a stochastic taxi pooling model incorporating stochastic vehicle travel times. A solution algorithm is also proposed to efficiently solve the problem. The performance of the proposed models and the use of the solution method in practice are evaluated by executing numerical tests using real data with suitable assumptions. The test results show that the stochastic model and the solution method could be useful references for practice.     

Long-term route traffic forecasts and flight schedule pattern for a medium-sized European airport

This paper develops a methodology for assessing the future route network and flight schedule at a medium-sized European airport. The starting point is the existing origin and destination demand from the base airport across the world. This is expanded using growth rates by country or region for the period up to year 2015. The future origin and destination demand is then converted into route traffic, subject to a threshold for direct service. Where demand falls below this level, traffic is reallocated via various appropriate hubs. A model of frequency and aircraft size is applied to estimate the future air service on each route and a schedule created, allocating these flights to specific times of day. The scenario where the base airport operates as a hub is then investigated. This involves identifying a suitable hub model, considering geographical and competitive issues. The origin and destination demand is increased, resulting in an enlarged network of routes. Flights are then scheduled within the constraints of an optimal wave pattern. The outputs are of considerable interest in long-term airport planning and also offer an insight into future airline network strategies and opportunities.     

On the multi-dimensionality and sampling of air transport networks

Complex network theory is a framework increasingly used in the study of air transport networks, thanks to its ability to describe the structures created by networks of flights, and their influence in dynamical processes such as delay propagation. While many works consider only a fraction of the network, created by major airports or airlines, for example, it is not clear if and how such sampling process bias the observed structures and processes. In this contribution, we tackle this problem by studying how some observed topological metrics depend on the way the network is reconstructed, i.e. on the rules used to sample nodes and connections. Both structural and simple dynamical properties are considered, for eight major air networks and different source datasets. Results indicate that using a subset of airports strongly distorts our perception of the network, even when just small ones are discarded; at the same time, considering a subset of airlines yields a better and more stable representation. This allows us to provide some general guidelines on the way airports and connections should be sampled.     

突发大客流在城市轨道交通网络中的传播机理

根据突发大客流在城市轨道交通车站的作业性质和特点,将城市轨道交通网络中的车站分为发生站、换乘站和中间站。在此基础上,通过站台候车区的乘客密度、到达列车的剩余载客能力、站台候车乘客数和乘客上车效率等因素,构建站台候车区乘客密度影响模型和列车运行延误时间模型,并总结出突发大客流在城市轨道交通网络中的传播机理。从车站服务水平和列车运行影响两个方面对突发大客流传播的影响因素及相应的调整措施进行分析。     

对双向系统编组站无改编折角列车径路的分析

随着路网的发展,双向系统编组站逐渐增多,这种编组站改编能力最大,最适合流水作业．但薄弱环节是如何处理好折角车流。分析无改编折角列车作业与枢纽总图布置及双向系统编组站的关系,探讨解决双向编组站无改编折角列车径路的方式,以利做出更好的设计,为运营创造良好的条件。     

Correlation analysis of day-to-day origin-destination flows and traffic volumes in urban networks

The trip patterns on an urban network can be represented by two main variables: origin-destination flows (OD flows), defined as the number of trips between two locations over a given time period, and traffic volumes, defined as the number of vehicles that cross a street over a given time interval. Past research on the dynamic of traffic assignment and OD estimation suggested that the traveler's decisions vary on a day-to-day basis and that their most recent decisions may affect their current travel decisions. Based on these assumptions, this study analyzed the autocorrelation of a set of day-to-day series of traffic volumes and OD flows generated from a large collection of traffic sensors, identifying the data's correlation structure over different locations and OD pairs in an urban network. To this end, a method for data treatment of the 2017 dataset from the traffic monitoring system of Fortaleza, Brazil, was employed, which consisted in the following major steps: data cleaning due to equipment failure, definition of traffic profiles for typical and atypical months, definition of daily traffic periods, selection of suitable devices to obtain OD flows, and detection of outliers in the time series. The traffic profiles and the daily traffic periods were defined by applying clustering techniques. The analysis of autocorrelation was performed after controlling for seasonal effects in the data by applying regression analysis. This study contributes to understand how the dynamic of trip patterns varies over space due to the spatial distribution of the city's activities and the network's spatial centrality. The analysis of 144 sets of traffic volumes throughout 2017 suggests that the autocorrelation of traffic volumes should be higher in congested central areas where multiple options of route are available. It seems that, for large congested networks, which present many uncertain factors (e.g., accidents, variable weather, multiple paths, etc.), part of the users do not have complete knowledge of the network's performance, and must rely on experience and habit to decide their routes, especially at more centralized locations of the network. The analysis of serial correlation in the series of sample OD flows between regions showed that the city's central area, where more commercial and service-related activities take place, seems to influence the dynamic of OD flows, probably due to the occurrence of more non-commuting trips to the central area of the city.     

Low-cost airlines and airport competition

An important question from the viewpoint of competition analysis in the air transport industry is the extent to which low-cost airlines operating from a secondary airport compete with full-service airlines serving a main airport in a multiple airport region. In this paper we address the issue of the competition between full-service and low-cost airlines serving adjacent airports in the Greater London using econometric estimation of demand structure (own- and cross-price elasticities). Our analysis follows the methodology in (Pels, E., Nijkamp, P., Rietveld, P., 2000. Airport and airline competition for passengers departing from a large metropolitan area. Journal of Urban Economics, 48 (1), 29–45, Pels, E., Nijkamp, P., Rietveld, P., 2003. Access to and competition between airports: a case study for the San Francisco Bay area. Transportation Research Part A: Policy and Practice, 37 (1), 71–83). It is based on the nested logit model which we use to capture three key dimensions of passenger choice: air fare, surface-access costs and frequency. We obtained estimates of the own- and cross-price elasticities, which was the focus of our interest. On the basis of our understanding of the industry dynamics we find these estimates, especially of the cross-price elasticities, to be on the low side.     

Impacts of high-speed rail lines on the city network in China

China's large-scale HSR network has a significant influence on both accessibility and connectivity, but little attention has been paid to its impacts on connectivity. Changes in connectivity largely affect the external relations among cities, thus influencing the structure of the city network. This paper examines the impacts of China's HSR network on the overall connectivity and nodal centrality of the city network, as evaluated by passenger trains from 2003 to 2014. This paper employs the graph index, average path length, clustering coefficient and three indicators of centrality, namely weighted degree centrality (WDC), weighted closeness centrality (WCC) and weighted betweenness centrality (WBC). The results show that the HSR network largely increased overall connectivity according to the increasing Beta index and clustering coefficient, and decreasing average path length. The HSR lines also increased the average centrality of the city network and the inequality of nodal centrality according to the WCC indicator, but they decreased the inequality of nodal centrality with regard to the WDC and WBC indicators. Meanwhile, the growing HSR network led to the centrality tended to intensify in large cities in terms of the WCC indicator, but intensify in small cities according to the WDC and WBC indicators. Spatially, the cities with HSR stations, population over 3 million and GDP over 100 billion RMB saw higher increases in centrality than the others; the cities with high values of WDC and WCC, especially the top 20 cities, tended to concentrate in the populous areas with well-developed economies (e.g., Yangtze River Delta), whereas the cities with high WBC values in 2014 were coupled with the hub cities of regional railway management administration.