Destination Pairs Research Articles

Trajectory Generation of Ultra-Low-Frequency Travel Routes in Large-Scale Complex Road Networks

Trajectory generation can help predict the future road network state and properly deal with the privacy issues of trajectory data usage. To solve the problem that routes with very few journeys (ultra-low-frequency journey routes) are difficult to generate in the large-scale complex road network scenarios, the study designs a framework focusing on ultra-low-frequency route generation, ULF-TrajGAIL, and proposes an original trajectory-augmentation method called the combined expansion method. The specific original trajectory-augmentation method is determined by the pre-trajectory-generation experiment, and high-quality synthetic trajectories with higher diversity and similarity are output based on the final generation experiments which take the augmented trajectories as references. Based on the real trajectories of a complex road network in a region of Guangzhou, the quality of synthetic trajectories under different original trajectory-augmentation methods from the route, link and origin and destination pairs levels has been compared. The results show that the method can generate more ultra-low-frequency routes and help improve the overall diversity of routes and the similarity between routes and the number of journeys as well.

TTS2016R: A data set to study population and employment patterns from the 2016 Transportation Tomorrow Survey in the Greater Golden Horseshoe area, Ontario, Canada

This paper describes and visualises the data contained within the {TTS2016R} data package created in R, the statistical computing and graphics language. {TTS2016R} contains home-to-work commute information for the Greater Golden Horseshoe area in Canada retrieved from the 2016 Transportation Tomorrow Survey (TTS). Included are all Traffic Analysis Zones (TAZ), the number of people who are employed full-time per TAZ, the number of jobs per TAZ, the count of origin destination (OD) pairs and trips by mode per origin TAZ, calculated car travel time from TAZ OD centroid pairs and associated spatial boundaries to link TAZ to the Canadian Census. To illustrate how this information can be analysed to understand patterns in commuting, we estimate a distance-decay curve (i.e. impedance function) for the region. {TTS2016R} is a growing open data product built on R infrastructure that allows for the immediate access of home-to-work commuting data alongside complimentary objects from different sources. The package will continue expanding with additions by the authors and the community at-large by requests in the future. {TTS2016R} can be freely explored and downloaded in the associated Github repository where the documentation and code involved in data creation, manipulation and all open data products are detailed.

Finding an energy efficient path for plug-in electric vehicles with speed optimization and travel time restrictions

Transportation is one of the main factors when global total energy consumption is considered and is a significant contributor to emissions of harmful gases including carbon dioxide (CO2). Due to their lower tailpipe CO2 emissions compared to the vehicles with internal combustion engines, electric vehicles provide an opportunity to reduce environmental impacts of transportation. In this direction, a problem for plug-in electric vehicles (PEVs) is studied where the aim is to find an energy efficient path. Given an origin–destination pair over a directed network, this problem involves determining a path joining origin and destination, the speed of the PEV on each road segment, i.e., arc, along the path, the charging stations the PEV will stop by, and how much to recharge at each stop so as to minimize the total amount energy consumption. There are speed limits on each road segment, and PEV has to arrive at the destination on or before a given total time limit. For this problem, firstly, a mixed-integer second order cone programming formulation (MISOCP) is proposed. Secondly, to be able to solve larger size instances, a matheuristic is developed. Lastly, an iterated local search (ILS) algorithm is designed for this problem. Solution quality and computation times of the heuristics and the exact algorithm are compared on different instances. Differently from the literature, the speed values of the PEV on the arcs are considered as continuous decision variables in all proposed solution approaches. Moreover, consideration of the speed limits which can be legal limits or limits imposed by congestion makes our problem more realistic. The analysis of the results of the computational experiments gives the user an insight to select the proper solution approach based on the instance settings. MISOCP formulation becomes inadequate for larger instances. On the other hand, the heuristic solution approaches can solve such instances within reasonable computational times and therefore they have the potential to be integrated in some software to dynamically find energy efficient paths.

Low Cost Online Network Traffic Measurement With Subspace-Based Matrix Completion

Traffic Matrix (TM) is important for network operation and management. However, it is hard to measure the complete TM due to the high measurement cost. Few recent studies propose using sparse measurement with only a subset of origin and destination pairs (OD pairs) while the other OD pairs are reconstructed through matrix completion. Although effective, current sparse network monitoring schemes can hardly support online network monitoring which requires scheduling the sample taking adaptively in each new time slot one by one. To meet the online network monitoring scenario, we propose a sparse network monitoring scheme by exploiting subspace-based matrix completion. Several novel techniques are proposed in our scheme. First, to capture the dynamic rank feature, we design the scheme based on sliding window and propose an algorithm to estimate the rank of current window even though we don't know the data of the upcoming time slot. Secondly, based on the rank estimated, we propose an adaptive sampling scheduling algorithm. Finally, we propose a lightweight algorithm to speed up the reconstruction process by reusing the matrix calculation results in the previous time slot. The experimental results demonstrate that our scheme guarantees the high precision of network-wide TM monitoring while significantly reducing the measurement cost.

Tripartite Graph Aided Tensor Completion For Sparse Network Measurement

Network measurements provide critical inputs for a wide range of network management. Existing network-wide monitoring methods face the challenge of incurring a high measurement cost. Some recent studies show that network-wide measurement data such as end-to-end latency and flow traffic, have hidden spatio-temporal correlations and thus low-rank features. Taking advantage of the low-rank feature, enlightened by tensor model's strong capability of information representation and extracting, this paper studies a novel sparse measurement scheduling problem which selects a proportion of Origin and Destination (OD) pairs to take measurements in the future time slots, while ensuring the data of the remaining un-measured OD pairs be accurately inferred through tensor completion. It is challenging to find the optimal sampling points (OD pairs) without knowing the structure of the future data and also infer the un-measured data in the presence of noise in the measurement samples. To conquer the challenges, we propose several techniques: a tripartite graph to illustrate the relationship between sample locations and tensor factorization, a graph-based sample selection algorithm, and a graph-based robust tensor completion algorithm. We have conducted extensive experiments based on two real network latency monitoring traces (PlanetLab and Harvard) and two other network monitoring traces (including a traffic trace Abilene and a throughput trace WS-Dream). Our results demonstrate that, even with a sampling ratio of less than 5%, our scheme can accurately obtain the complete network-wide monitoring data by inferring the missing ones based on the samples taken. To achieve similar recovery performance, the best peer tensor completion algorithm needs a significantly larger number of samples, with the sampling ratio up to 25-150 times ours.

Transshipment network design for express air cargo operations in China

We introduce a novel multimodal (ground and air transportation) network design model with transshipments for the transport of express cargo with heterogeneous service classes (i.e., next morning delivery, and next day delivery). We formulate this problem using a novel path-based mixed-integer program which seeks to maximize the demand (weight) served. We investigate the value of the proposed transshipment network under various operational conditions and by benchmarking against a direct shipment network and a network with a single transshipment point which mimics a classical star-shaped hub-and-spoke network. Our extensive computational study with real-world data from ShunFeng (SF) Express reveals that the integration of ground and air transportation improves the coverage and that transshipment enables serving a large number of origin–destination pairs with a small number of cargo planes. Importantly, we show that by simplifying handling, i.e., employing cross-docking rather than time-consuming sortation, a transshipment network can transport express cargo fast enough to meet demanding delivery deadlines. Finally, we find that increasing the efficiency of intra-city operations and extending the nightly operating time window are the most effective operational adjustments for further improving the performance of the proposed transshipment network.

Two new mixed‐integer programming models for the integrated train formation and shipment path optimization problem

AbstractRailcars are known as the heart of the freight rail transportation industry. Hence, any improvements in their operations can lead to sharp reductions in various operating costs. One of the most critical operations on railcars is blocking and routing their transportation. Railway companies face continuous challenged about what blocks should be formed to carry shipments across different origin–destination pairs (O–D pairs) and reclassify them in intermediate yards to minimize transportation reclassification costs. In addition, it is necessary to determine train service between O–D pairs and the number of trains. Along with the shipment routing plans, this problem is called train formation and shipment path optimization (TFSP). In TFSP, some substructure and rail network operational constraints should be considered, including link capacity, classification capacity, the number of sorting tracks, and path length. This paper presents two arc‐based mixed‐integer linear programming (MILP) models to formulate the TFSP problem. To the best of the authors' knowledge, no MILP arc‐based model has been published for the problem that does not need any preprocess before solving. Computational results of solving models on the datasets showed that the first model could obtain a feasible solution with a maximum 0.05% gap up to 48 yards instance. The second model also could find a solution with a small gap compared to the optimal solution in a reasonable time for instances up to 128 yards. Also, the proposed models were compared to the best methods in the literature, and their superiority was shown.

Wind-optimal lateral trajectories for a multirotor aircraft in urban air mobility

The primary motivation for this paper is to quantify the operational benefits (energy consumption and flight duration) of flying wind-optimal lateral trajectories for short flights (less than 60 miles) anticipated in the urban environment. The optimal control model presented includes a wind model for quantifying the effect of wind on the lateral trajectory. The optimal control problem is numerically solved using the direct collocation method. Energy consumption and flight duration flying wind-optimal lateral trajectories are compared with corresponding values obtained flying great-circle paths between the same origin and destination pairs to determine the operational benefits of wind-optimal routing for short flights. The flight duration results for different scenarios are validated using a simulation tool designed and developed at NASA for exploring advanced air traffic management concepts. This research study suggests that for short flights in an urban environment, operational benefits of the wind-optimal lateral trajectories over the corresponding great-circle trajectories in terms of energy consumption and flight duration per flight are dependent on: i) wind field’s spatial variability, ii) wind magnitude, iii) the direction of route relative to the wind field, and iv) cruise segment length. The operational benefits observed in realistic flyable wind scenarios are less than 2.5%; these could be translated to an equivalent of a maximum of 2 min of cruise flight duration savings in the urban air mobility environment. As expected, headwinds and tailwinds along the flight route most significantly impact energy consumption and flight duration.

A mean-CVaR approach to the risk-averse single allocation hub location problem with flow-dependent economies of scale

The hub location problem (HLP) is a fundamental facility planning problem with various applications in transportation, logistics, and telecommunication systems. Due to strategic nature of the HLP, considering uncertainty and the associated risks is of high practical importance in designing hub networks. This paper addresses a risk-averse single allocation HLP, where the traffic volume between the origin–destination (OD) pairs is considered to be uncertain. The uncertainty in demands is captured by a finite set of scenarios, and a flow-dependent economies of scale scheme is used for transportation costs, modeled as a piece-wise concave function of flow on all network arcs. The problem is cast as a risk-averse two-stage stochastic problem using mean-CVaR as the risk measure, and a novel solution approach combining Benders decomposition and scenario grouping is proposed. An extensive set of computational experiments is conducted to study the effect of different input parameters on the optimal solution, and to evaluate the performance of the proposed solution algorithm. Managerial insights are derived and presented based on the obtained results.

Secured Data Transmission Over Insecure Networks-on-Chip by Modulating Inter-Packet Delays

As the network-on-chip (NoC) integrated into an SoC design can come from an untrusted third party, there is a growing risk that data integrity and security get compromised when supposedly sensitive data flows through such an untrusted NoC. We thus introduce a new method that can ensure secure and secret data transmission over such an untrusted NoC. Essentially, the proposed scheme relies on encoding binary data as delays between packets travelling across the source and destination pair. The maximum data transmission rate of this inter-packet-delay (IPD)-based communication channel can be determined from the analytical model developed in this article. To further improve the undetectability and robustness of the proposed data transmission scheme, a new block coding method and communication protocol are also proposed. Experimental results show that the proposed IPD-based method can achieve a packet error rate (PER) of as low as 0.3% and an effective throughput of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\boldsymbol {2.3\times 10^{5}}$ </tex-math></inline-formula> b/s, outperforming the methods of thermal covert channel, cache covert channel, and circuit-based encryption and, thus, is suitable for secure data transmission in unsecure systems.

Analyzing connectivity reliability and critical units for highway networks in high-intensity seismic region using Bayesian network

It is important to evaluate the connectivity reliability of highway networks for the emergency response and rehabilitation of transportation systems in high-intensity seismic regions. Given the complexity and uncertainty of seismic damages of highway networks in high-intensity seismic region, this paper describes a Bayesian network (BN) model for evaluating the network connectivity reliability and identifying critical units. The empirical prediction method is employed to compute the connectivity probability of highway units based on the structural damage of units under earthquakes. A success tree is used to construct the network connectivity graph. Then, the network connectivity graph is converted into the BN model by BN method with the connectivity probability of highway units as prior probability. Sensitivity analysis and Bayesian updating are performed in BN to identify critical units and dynamically assess the connectivity reliability of highway network. The proposed model is applied to a highway network composed of G213 and S9 in the Wenchuan Earthquake. The results show that the BN model integrates the structural damage of units with the functional performance of the highway network in high-intensity seismic region. Bayesian updating allows the posterior probability of segments and origin–destination pairs to be computed, providing an online evaluation of the functional performance of the highway network. The identification of critical units at each stage enables seismic reinforcement priority, thus contributing to the rehabilitation on connectivity reliability of network system.

How to trade thirty thousand products: A wholesale market design for road capacity

One of the core reasons for urban traffic congestion is the mispricing of the traffic’s main resource, the scarce road capacity. Recent proposals suggest a two-stage market for road capacity similar to other major utilities markets such as those for electricity. In such markets an Independent System Operator (ISO) provides road infrastructure which multiple Service Providers (SP) then resell to end consumers. The size of such markets in terms of the number of traded items, road segments per hour, is exceptional. A road network in a city consists of tens of thousands different road segments and it is unclear how a wholesale market for service providers should be designed to keep it tractable for buyers and sellers. Three problems arise in this context: First, how can a service provider express preferences for so many products. Second, the optimization problem is very large and it is far from obvious that problems of this size can be solved. Finally, the allocation problem is non-convex and finding competitive equilibrium prices on such markets is impossible in general. We suggest a parsimonious bid language based on origin–destination pairs and introduce a mixed-integer optimization problem to maximize welfare on such markets. Based on the MATSim traffic simulator, we show that one can solve realistic problems based on traffic data for the city of Berlin to optimality within 15 minutes. Importantly, we approximate competitive equilibrium prices which require only negligible side-payments as the allocation problem is “almost” convex. Overall, the paper provides a tangible proposal for wholesale markets for road capacity.

Bi-level clustering of vehicle trajectories for path choice set and its nested structure identification

Path choice set identification is essential for route choice modelling and travel behaviour studies. Recent advancements in data collection techniques have gained attention towards a data-driven choice set identification process. However, empirical vehicle trajectory datasets result in several path observations compared to the traditional algorithms, complicating the route choice modelling process. This study proposes a bi-level vehicle trajectory clustering framework where the output of the upper-level clustering provides a representative path choice set for simple/mixed logit modelling (MNL), whereas the lower-level clustering provides a nested or cross-nested representation of the paths based on hard and soft clustering, respectively.As proof of concept, the proposed methodology is applied on real Bluetooth-based trajectories from Brisbane, where 62 unique paths were observed from a one-year trajectory data for an origin–destination pair. The results of the MNL model for the representative paths provide desirable magnitude with negative coefficients for the distance and travel time path attributes. Further, the results of the (cross) nested modelling appropriately identified the (cross) nested structure for the path choice set.

Bus travel time reliability incorporating stop waiting time and in-vehicle travel time with AVL data

Improving bus travel time reliability can attract more commuters to use bus transit, and therefore reduces the share of cars and alleviates traffic congestion. This paper formulates a new bus travel time reliability metric that jointly considers two stochastic processes: the in-stop waiting process and in-vehicle travel time process, and the bus travel time reliability function is calculated by the convolution of independent events’ probabilities. The new reliability metric is defined as the probability when bus travel time is less than a certain threshold and can be used in both conditions with and without bus transfer. Next, Automatic Vehicle Location (AVL) data of the city of Harbin is used to demonstrate the applicability of the proposed method. Results show that factors such as weather, day of the week, departure time, travel distance, and the distance from the boarding stop to the bus departure station can significantly affect the travel time reliability. Then, a case with low bus departure frequency is analyzed to show the impact of travelers’ arrival distribution on their bus travel time reliability. Further, it is demonstrated that the travel time reliabilities of two bus transfer schemes of the same Origin–Destination (O–D) pair can have significantly different patterns. Understanding the bus travel time reliability pattern of the alternative bus routes can help passengers to choose a more reliable bus route under different conditions. The proposed bus travel time reliability metric is tested to be sensitive to the effect of different factors and can be applied in bus route recommendation, bus service evaluation, and optimization.

Transfer Penalty Estimation of Bus Passengers Considering Travel Frequency in Chengdu, China

The paper aims to examine bus passengers’ route choice behavior in the context of transfer penalty estimation. Methodologically, it leverages passengers’ stop-level trip information inferred from automatic vehicle location (AVL) and automated fare collection (AFC) data and compares the stop-level origin–destination (O-D) pairs with direct paths and transfer paths. The route choice models were established with the inclusion of normalized travel frequency as a key variable. A case study was performed using the trip data of adult card holders from the bus systems in Chengdu, China. The results show that the normalized travel frequency is a variable that makes an informative contribution to the explanation of passenger route choices. Specifically, passengers with higher travel frequency prefer to choose the transfer path. Moreover, the transfer penalty function in the context of the monthly travel frequency was obtained and shows that the travel frequency can reduce a passenger’s transfer penalty. Finally, the stabilities of the normalized travel frequency function and transfer penalty function were assessed using the trip data from the weekdays in four weeks with the results showing that the normalized travel frequency function is similar in shape. In addition, the relationship between a passenger’s monthly travel frequency and their familiarity with the bus network was discussed using the second derivative of the normalized travel frequency function.

Hub location problem considering spoke links with incentive-dependent capacities

This study proposes a hub-and-spoke (HS) network in which the capacity of a spoke link depends on the incentive provided to the transporters. The incentives influence the capacities of the spoke links, which in turn affect the hub selections and flow assignment. A mixed integer convex programming model is developed to optimize the proposed HS network. The model minimizes total transport cost by locating p hubs, routing flows between origin–destination (OD) pairs and determining the incentives on spoke links. A customized outer-approximation algorithm is presented to provide exact solutions to the developed model, which is difficult to solve optimally within acceptable computational times for large-scale instances. An approximation algorithm based on the stepwise linearization method is then developed to provide suboptimal solutions. The developed model and algorithms are validated in computational experiments with different problem scales. The experiments demonstrate that the proposed HS network tends to route the flows on more spoke links, balance the transport costs on the potential paths between OD pairs and serve more demands with lower transport costs, when compared with the HS network with fixed capacities.

Proactive Resilience Building through Route Diversity: A Close Look at the Metro System from the Travelers’ Perspective

Travel demand plays a moderate role in the resilience impact assessment of public transport network disruptions. We analyze how travelers can proactively build transport resilience by responding to adverse events using alternative routes. We consider route diversity (i.e., the numbers of alternative routes for all origin–destination (OD) pairs) as a measure of the network’s capability to accommodate route choice behavioral change and look for potential proactive travelers from the spatial distribution of OD pairs with alternative routes in the Beijing subway network. We further investigate how proactive resilience can be built by choosing alternative routes with the least extra time cost.

Route choice estimation in rail transit systems using smart card data: handling vehicle schedule and walking time uncertainties

Several cities around the world rely on urban rail transit systems composed of interconnected lines, serving massive numbers of passengers on a daily basis. Accessing the location of passengers is essential to ensure the efficient and safe operation and planning of these systems. However, passenger route choices between origin and destination pairs are variable, depending on the subjective perception of travel and waiting times, required transfers, convenience factors, and on-site vehicle arrivals. This work proposes a robust methodology to estimate passenger route choices based only on automated fare collection data, i.e. without privacy-invasive sensors and monitoring devices. Unlike previous approaches, our method does not require precise train timetable information or prior route choice models, and is robust to unforeseen operational events like malfunctions and delays. Train arrival times are inferred from passenger volume spikes at the exit gates, and the likelihood of eligible routes per passenger estimated based on the alignment between vehicle location and the passenger timings of entrance and exit. Applying this approach to automated fare collection data in Lisbon, we find that while in most cases passengers preferred the route with the least transfers, there were a significant number of cases where the shorter distance was preferred. Our findings are valuable for decision support among rail operators in various aspects such as passenger traffic bottleneck resolution, train allocation and scheduling, and placement of services.

Topological Approach for Optimizing Railroad Freight Network Restoration after Disruptions

A topology-based method is proposed for optimizing the restoration sequence of damaged components in a disrupted rail freight network. Formulated as a demand-weighted average of reciprocal shortest path lengths, network efficiency is used as an indicator of overall connectivity for origin–destination (OD) pairs having freight demand. With the fixed demand matrix, a given network configuration, and a given disruption scenario, the cumulative loss of network efficiency during the restoration process is computed for each evaluated restoration sequence, using network efficiency values in intermediate network states as well as the duration of each restoration phase (i.e., restoration plus access time). This cumulative loss is treated as a measure of post-disruption network resilience, and is minimized with a simple genetic algorithm (GA) that finds the corresponding optimized restoration sequence, which also determines the optimized restoration schedule. The proposed method is demonstrated in a synthesized numerical case of a small network and a disruption scenario. The GA can find the globally optimal restoration sequence relatively fast, with its effectiveness further verified through exhaustive enumeration for three additional disruption scenarios. Sensitivity analysis results indicate that higher topological centrality and freight throughput of damaged nodes or disruption-induced isolation of some nodes are responsible for higher minimized loss of cumulative efficiency. The optimized restoration sequence tends to prioritize nodes and adjacent links with relatively high freight throughput in normal operation.

Investigating Factors Related to Criminal Trips of Residential Burglars Using Spatial Interaction Modeling

This study used spatial interaction modeling to examine whether origin-specific and destination-specific factors, distance decay effects, and spatial structures explain the criminal trips of residential burglars. In total, 4041 criminal trips committed by 892 individual offenders who lived and committed residential burglary in Tokyo were analyzed. Each criminal trip was allocated to an origin–destination pair created from the combination of potential departure and arrival zones. The following explanatory variables were created from an external dataset and used: residential population, density of residential burglaries, and mobility patterns of the general population. The origin-specific factors served as indices of not only the production of criminal trips, but also the opportunity to commit crimes in the origin zones. Moreover, the criminal trips were related to the mobility patterns of the general population representing daily leisure (noncriminal) trips, and relatively large origin- and destination-based spatial spillover effects were estimated. It was shown that considering not only destination-specific but also origin-specific factors, spatial structures are important for investigating the criminal trips of residential burglars. The current findings could be applicable to future research on geographical profiling by incorporating neighborhood-level factors into existing models.