Static Road Network Research Articles

Real-Time Insertion Operator for Shared Mobility on Time-Dependent Road Networks

One of the most important challenges in shared mobility services ( e.g. , ride-sharing and parcel delivery) is planning routes for workers by considering real road conditions. To tackle this challenge, the "insertion operator", which computes the optimal route for the worker to serve ( i.e. , insert) the newly appeared delivery request, has been acted as the fundamental operation in existing solutions. However, existing works implicitly assume a static road network, hence are hard to fulfill the real-world scenario, where travel time between two locations is not constant at different times of a day. By contrast, we focus on the insertion operator over time-dependent road networks that capture the periodic pattern of road conditions. We also show that the time complexity of existing solutions would degrade into cubic time and hence such solutions can no longer satisfy the real-time requirement under this real-world setting. To satisfy the need for real-time computation, we propose a data summary to model the time-dependent travel time functions between pairs of vertices in the route. Based on the data summary, we design an efficient solution that can enumerate the best insertion position in linear time while satisfying complex spatiotemporal constraints. Finally, extensive experiments are conducted on real datasets from several applications of shared mobility. The results show that our solution is up to 44.5X faster than the state-of-the-art solution.

Fully Dynamic Contraction Hierarchies with Label Restrictions on Road Networks

In the real world, road networks with weight and label on edges can be applied in several application domains. The shortest path query with label restrictions has been receiving increasing attention recently. To efficiently answer such kind of queries, a novel index, namely Contraction Hierarchies with Label Restrictions (CHLR), is proposed in the literature. However, existing studies mainly focus on the static road networks and do not support the CHLR maintenance when the road networks are dynamically changed. Motivated by this, in this paper, we investigate the CHLR maintenance problem in dynamic road networks. We first devise a baseline approach to update CHLR by recomputing the potential affected shortcuts. However, many shortcuts recomputed in baseline do not change in fact, which leads to unnecessary overhead of the baseline. To overcome the drawbacks of baseline, we further propose a novel CHLR maintenance algorithm which can only travel little shortcuts through an update propagate chain with accuracy guarantee. Moreover, an optimization strategy is presented to further improve the efficiency of index maintenance. Considering the frequency of edge changes, we also propose a batch index maintenance algorithm to handle batch edge changes which can process a large number of edge changes at once. Furthermore, a parallel method is proposed to further accelerate calculations. Extensive and comprehensive experiments are conducted on real road networks. The experimental results demonstrate the efficiency and effectiveness of our proposed algorithms.

Decentralized multi-agent approach based on A* algorithm for on-demand transport problem

The on-demand transport (ODT) systems have developed worldwide as they have significant social, environmental, and economic benefits. Even with those benefits, it’s still important to gain popular acceptance. The acceptance key is the reactivity of the system in providing fast and reliable solutions whilst respecting vehicles’ and clients’ constraints. This paper presents a decentralized multi-agent approach to model and solve the ODT problem in a static road network. The agents interact with each other using the A* algorithm to find an optimal solution for each transport demand. The optimal solution is expressed by the fastest trajectory taken by the cheapest vehicles. We utilize factual data from a Lebanese city to do experiments evaluating the proposed approach.

Coordinating Multiple Cooperative Vehicle Trajectories on Shared Road Networks

This paper addresses the problem of planning trajectories for multiple cooperative agents along specified paths through a static road network. Vehicle trajectories are coupled through interactions at shared areas, including intersections and road segments. A motion model is presented that includes the combined trajectories of all vehicles. The trajectories are optimized for travel time by solving a Mixed Integer Linear Program (MILP) that incorporates constraints to ensure collision avoidance. To improve the computation time of solving the MILP, two model modifications are introduced related to interactions: 1) The use of binary variables is reduced by grouping them at targeted travel times. 2) The relative travel order of interacting vehicles is constrained, guided by a heuristic solver. To further reduce computation time, an iterative method solves a sequence of smaller MILPs by targeting essential vehicle interactions with an algorithm that predicts interactions. Experiments are run on a simulated road network based on a real surface mine and haul truck trips. The proposed MILP methods are shown to significantly reduce solution costs compared to a reactive approach based on common driving practices. The MILP modifications significantly reduce computation time, trading off marginal solution quality. The reduction is extended by the iterative MILP scheme without degradation of solution quality.

Efficient kNN query for moving objects on time-dependent road networks

In this paper, we study the Time-Dependent k Nearest Neighbor (TD-kNN) query on moving objects that aims to return k objects arriving at the query location with the least traveling cost departing at a given time t. Although the kNN query on moving objects has been widely studied in the scenario of the static road network, the TD-kNN query tends to be more complicated and challenging because under the time-dependent road network, the cost of each edge is measured by a cost function rather than a fixed distance value. To tackle such difficulty, we adopt the framework of GLAD and develop an advanced index structure to support efficient fastest travel cost query on time-dependent road network. In particular, we propose the Time-Dependent H2H (TD-H2H) index, which pre-computes the aggregated weight functions between each node to some specific nodes in the decomposition tree derived from the road network. Additionally, we establish a grid index on moving objects for candidate object retrieval and location update. To further accelerate the TD-kNN query, two pruning strategies are proposed in our solution. Apart from that, we extend our framework to tackle the time-dependent approachable kNN (TD-AkNN) query on moving objects targeting for the application of taxi-hailing service, where the moving object might have been occupied. Extensive experiments with different parameter settings on real-world road network show that our solutions for both TD-kNN and TD-AkNN queries are superior to the competitors in orders of magnitude.

Multi-View Spatial–Temporal Graph Neural Network for Traffic Prediction

Abstract Spatial–temporal graph neural network has drawn more and more attention in recent years and is widely used to various real-world applications. However, learning the spatial–temporal graph neural network structure presents unique challenges including: (i) the dynamic spatial correlation; (ii) the dynamic temporal correlation. Even the existing methods take into account the spatial correlation, they still learn the static road network structure information, which cannot reflect the dynamic of road relations. Some of the works has focused on modeling the long-term time series, but the improvements have been limited tightly. To overcome these challenges, we proposed a novel approach called Multi-View Spatial–Temporal Graph Neural Network. Differ from the existing research, we designed a multi-view temporal transformer module to extract dynamic temporal correlation and enhance the expression of medium and long-term temporal features. We propose a multi-view spatial structure and a corresponding multi-view graph convolutional module, which are capable of simultaneously combining the features of static road network structure and dynamic changes. Compared with 11 baselines, our proposed model has achieved significant improvement in the accuracy of prediction.

Scenic Tourist Route Planning Algorithm Based on Mobile Computing and Grey Entropy Decision Model

Since the concept of “Smart Earth” was put forward, countries have attached great importance to the research and introduction of smart tourism. With the increasing updating of information technology, the tourism industry is also constantly trying to transform intelligently, and the personalized recommendation of its travel routes has become the most important development in smart tourism, one of the hot topics. Tourism agencies create traditional travel itineraries based on the preferences of the majority of people and the characteristics of tourist attractions. These lines are primarily used for team travel. People’s expectations for travel route planning are increasing as their living standards rise, and the traditional route planning algorithm based on a static road network data model has struggled to describe the complex and changing scenic environment. The improved random walk algorithm suggests suitable travel routes to users, allowing for more accurate route recommendations and effectively addressing the problem of new route recommendation difficulty. This paper proposes a scenic tourist route planning algorithm using the grey entropy decision-making model and mobile computing. The content of the recommended results is more closely related to the target recommendation user’s tendency after personalized adjustment, which has a better effect on the personalization of the recommended results.

Path planning of scenic spots based on improved A* algorithm

Traditional scenic route planning only considers the shortest path, which ignores the information of scenic road conditions. As the most effective direct search method to solve the shortest path in static road network, A* algorithm can plan the optimal scenic route by comprehensively evaluating the weights of each expanded node in the gridded scenic area. However, A* algorithm has the problem of traversing more nodes and ignoring the cost of road in the route planning. In order to bring better travel experience to the travelers, the above factors are taken into account. This paper presents a path planning method based on the improved A* algorithm. Firstly, the heuristic function of the A* algorithm is weighted by exponential decay to improve the calculation efficiency of the algorithm. Secondly, in order to increase the practicality of the A* algorithm, the impact factors that road conditions is introduced to the evaluation function. Finally, the feasibility of the improved A* algorithm is verified through simulation experiments. Experimental results show that the improved A* algorithm can effectively reduce the calculation time and road cost.

Efficient Processing of All Nearest Neighbor Queries in Dynamic Road Networks

The increasing trend of GPS-enabled smartphones has led to the tremendous usage of Location-Based Service applications. In the past few years, a significant amount of studies have been conducted to process All nearest neighbor (ANN) queries. An ANN query on a road network extracts and returns all the closest data objects for all query objects. Most of the existing studies on ANN queries are performed either in Euclidean space or static road networks. Moreover, combining the nearest neighbor query and join operation is an expensive procedure because it requires computing the distance between each pair of query objects and data objects. This study considers the problem of processing the ANN queries on a dynamic road network where the weight, i.e., the traveling distance and time varies due to various traffic conditions. To address this problem, a shared execution-based approach called standard clustered loop (SCL) is proposed that allows efficient processing of ANN queries on a dynamic road network. The key concept behind the shared execution technique is to exploit the coherence property of road networks by clustering objects that share common paths and processing the cluster as a single path. In an empirical study, the SCL method achieves significantly better performance than competitive methods and efficiently reduces the computational cost to process ANN queries in various problem settings.

Spatio-Temporal Reachable Area Calculation Based on Urban Traffic Data

The spatio-temporal reachable area that can be reached by driving vehicles from a specific starting location at starting time during a given time period is widely used in urban applications, such as the online ride-hailing service and the charging station seeking by an electric car. Existing studies on this issue usually utilize the static road network, which implies the spatial features, whereas the temporal characteristics of the dynamic urban traffic have not been explored in depth. In this article, we propose a spatio-temporal reachable area calculation scheme, named STRC, based on a tremendous amount of vehicle trajectory data. In STRC, the objective trajectory fragments are extracted according to the starting node and the query time period, and then mapped to reachable nodes to reduce the computational complexity. From those reachable road segments having reachable nodes on, a boundary segment is selected in each sector area by using the arrival-based one segment policy for time-sensitive applications or the arrival-and-distance-based k -segment policy for distance-related applications. The experiments based on large-scale trajectory data from 34 040 taxis in Beijing for one month show that STRC outputs more accurate reachable area, which covers the trajectory points with much smaller area, than compared schemes.

Identification of critical roads in urban transportation network based on GPS trajectory data

This study proposes a novel identification method of critical roads based on the combination of GPS trajectory data and directed weighted complex network. First, with both the static road network topology and the dynamic traffic flow characteristics taken into account simultaneously, a new spatial temporal model of urban transportation, namely a directed weighted complex network, is proposed. Then, combining the structure of road network with the strength influence of traffic between adjacent roads, a mixed influence-based identification algorithm of critical roads is proposed. Finally, we analyze taxi-GPS trajectory data collected in Lanzhou, China. We perform a comprehensive analysis to visualize the spatial–temporal changes of taxi services, critical roads, and critical intersections. Moreover, the correlation coefficient has been used to evaluate the performance of the identification algorithm of critical roads. The results show that the new identification algorithm is more effective and practical than traditional congestion index analysis. Our investigation should be helpful in urban traffic management and the residential choice of alternative routes.

Direction-aware KNN queries for moving objects in a road network

Recently more and more people focus on k-nearest neighbor (KNN) query processing over moving objects in road networks, e.g., taxi hailing and ride sharing. However, as far as we know, the existing k-nearest neighbor (KNN) queries take distance as the major criteria for nearest neighbor objects, even without taking direction into consideration. The main issue with existing methods is that moving objects change their locations and directions frequently over time, so the information updates cannot be processed in time and they run the risk of retrieving the incorrect KNN results. They may fail to meet users’ needs in certain scenarios, especially in the case of querying k-nearest neighbors for moving objects in a road network. In order to find the top k-nearest objects moving toward a query point, this paper presents a novel algorithm for direction-aware KNN (DAKNN) queries for moving objects in a road network. In this method, R-tree and simple grid are firstly used as the underlying index structure, where the R-tree is used for indexing the static road network and the simple grid is used for indexing the moving objects. Then, it introduces the notion of “azimuth” to represent the moving direction of objects in a road network, and presents a novel local network expansion method to quickly judge the direction of the moving objects. By considering whether a moving object is moving farther away from or getting closer to a query point, the object that is definitely not in the KNN result set is effectively excluded. Thus, we can reduce the communication cost, meanwhile simplify the computation of moving direction between moving objects and query point. Comprehensive experiments are conducted and the results show that our algorithm can achieve real-time and efficient queries in retrieving objects moving toward query point in a road network.

A Novel Index Method for K Nearest Object Query over Time‐Dependent Road Networks

K nearest neighbor (kNN) search is an important problem in location-based services (LBS) and has been well studied on static road networks. However, in real world, road networks are often time‐dependent; i.e., the time for traveling through a road always changes over time. Most existing methods for kNN query build various indexes maintaining the shortest distances for some pairs of vertices on static road networks. Unfortunately, these methods cannot be used for the time‐dependent road networks because the shortest distances always change over time. To address the problem of kNN query on time‐dependent road networks, we propose a novel voronoi‐based index in this paper. Furthermore, we propose a novel balanced tree, named ‐, which is a secondary level index on voronoi‐based index to make our querying algorithm more efficient. Moreover, we propose an algorithm for preprocessing time‐dependent road networks such that the waiting time is not necessary to be considered. We confirm the efficiency of our method through experiments on real‐life datasets.

Mobile Edge Computing-Enhanced Proximity Detection in Time-Aware Road Networks

Given a set of moving objects as well as their friend relationships, a time-aware road network, and a time threshold per friend pair, the proximity detection problem in time-aware road networks is to find each pair of moving objects such that the time distance (defined as the shortest time needed for two moving objects to meet each other) between them is within the given threshold. The problem of proximity detection is often encountered in autonomous driving and traffic safety related applications, which require low-latency, real time proximity detection with relatively low communication cost. However, (i) most existing proximity detection solutions focus on the Euclidean space which cannot be used in road network space, (ii) the solutions for road networks focus on static road networks and do not consider time distance and thus cannot be applied in time-aware road networks, and (iii) there are no works aiming to simultaneously reduce the communication cost, the communication latency, and computational cost. Motivated by these, we first design a low-latency proximity detection architecture based on Mobile Edge Computing (MEC) with the purpose of achieving low communication latency, then propose a proximity detection method including a client-side algorithm and a server-side algorithm, aiming at reducing the communication cost, and subsequently propose server-side computational cost optimization techniques to reduce the computational cost. Experimental results show that our MEC enhanced proximity detection architecture, our proximity detection method, and the server-side computational cost optimization techniques can reduce the communication latency, the communication cost, and the computational cost effectively.

Supporting Continuous Skyline Queries in Dynamically Weighted Road Networks

The paper focuses on the design of an optimum method for handling the continuous skyline query problem in road networks. Existing studies on processing the continuous skyline query focus exclusively on static road networks, which are limited because the state of roads in road networks is constantly changing. Therefore, to apply current methods for dynamically weighted road networks, a distributed skyline query method based on a grid partition method has been proposed in this paper. The method adopts the concepts of a distributed computing framework and road network preprocessing computations in which multiple parallel computing nodes are allocated and organized in grids. Using this approach, the road network map is simplified to a hub graph with much smaller scale such that the query load of the central node can be significantly reduced. The theoretical analysis and experimental results both indicate that, by using the proposed method, the system can achieve quick response time for users as well as a good balance between response times and accuracy. Therefore, it can be concluded that using the proposed method is beneficial for handling continuous skyline queries in a dynamically weighted road network.

Effective Urban Structure Inference from Traffic Flow Dynamics

Mobility in a city is represented as traffic flows in and out of defined urban travel or administrative zones. While the zones and the road networks connecting them are fixed in space, traffic flows between pairs of zones are dynamic through the day. Understanding these dynamics in real time is crucial for real time traffic planning in the city. In this paper, we use real time traffic flow data to generate dense functional correlation matrices between zones during different times of the day. Then, we derive optimal sparse representations of these dense functional matrices, that accurately recover not only the existing road network connectivity between zones, but also reveal new latent links between zones that do not yet exist but are suggested by traffic flow dynamics. We call this sparse representation the time-varying effective traffic connectivity of the city. A convex optimization problem is formulated and used to infer the sparse effective traffic network from time series data of traffic flow for arbitrary levels of temporal granularity. We demonstrate the results for the city of Doha, Qatar on data collected from several hundred bluetooth sensors deployed across the city to record vehicular activity through the city's traffic zones. While the static road network connectivity between zones is accurately inferred, other long range connections are also predicted that could be useful in planning future road linkages in the city. Further, the proposed model can be applied to socio-economic activity other than traffic, such as new housing, construction, or economic activity captured as functional correlations between zones, and can also be similarly used to predict new traffic linkages that are latently needed but as yet do not exist. Preliminary experiments suggest that our framework can be used by urban transportation experts and policy specialists to take a real time data-driven approach towards urban planning and real time traffic planning in the city, especially at the level of administrative zones of a city.

Within Skyline Query Processing in Dynamic Road Networks

The continuous within skyline query is an important type of location-based query, which can provide useful skyline object information for the user. Previous studies on processing the continuous within skyline query focus exclusively on a static road network, where the object attributes and the conditions of roads remain unchanged. However, in real-world applications, object attributes and road conditions inevitably vary with time, which severely limits the applicability of previous studies in practice. Therefore, in this paper, we address the issue of efficiently processing the continuous within skyline query in dynamic road networks with time-varying information. We design three elaborate data structures, the object attribute dominating matrix (OADM), the road distance sorted list (RDSL) and the skyline object expansion tree (SOET), to maintain the information of objects and the road network. Combined with OADM, RDSL and SOET, we develop an efficient algorithm, namely the within skyline object updating algorithm, to provide real-time processing of the time-varying information. Finally, a thorough experimental evaluation is conducted to show the merits of the proposed approaches.

Constrained energy-efficient routing in time-aware road networks

Routing problems find applications in many location-based services. Existing works which answer route queries mainly focus on static road networks rather than time-aware road networks. Observe the fact that (i) the same road segment may be driven with different speeds during different time intervals, and (ii) users usually prefer driving on a route that consumes minimum energy within a travel time budget. Motivated by this, this paper proposes the Constrained Energy-Efficient Time-Aware Routing problem, denoted as CEETAR. We take time factor into consideration and utilize a time-aware speed model and a time-aware polynomial energy cost model. To solve CEETAR, we propose a dynamic programming solution, and then propose an approximation algorithm which uses the branch and bound, and scaling strategy with provable approximation bounds to answer the query of CEETAR in real-world dense road networks. In addition, we also propose a greedy route planning algorithm. Experimental results demonstrate that our approximation algorithms can efficiently answer CEETAR queries with high accuracy.

Research on Dynamic Path Selection Improved Dijkstra Algorithm

Dynamic path selection algorithm is one of the most important researches in Intelligent Transportation System (ITS). After comparing in this article, we select Dijkstra algorithm as the optimal path algorithm. The traditional algorithm applies only to the static road network, the improved algorithm obtained optimal path planning program in the dynamic path selection. Finally, the combination of a numerical example, the improved algorithm for real-time, dynamic, effectiveness is verified through computer simulation. The accuracy of the prediction of the traffic flow plays a key role in the path planning, and the fusion forecast information dynamic path selection problem has important practical significance.

A collaborative approach to moving [formula omitted]-nearest neighbor queries in directed and dynamic road networks

In this paper, we investigate a new approach to moving k-nearest neighbor (MkNN) queries in directed and dynamic road networks, where each road segment has a particular orientation and its travel time changes depending on traffic conditions. An MkNN query continuously finds the k nearest neighbors (NNs) of a moving query object. Most existing studies have focused on MkNN queries in undirected and static road networks, where each road segment is bidirectional and its travel time does not change over time. However, little attention has been paid to MkNN queries in directed and dynamic road networks. In this research, we propose COMET, a collaborative approach to Moving k nEaresT neighbor queries in directed and dynamic road networks, where query processing is performed through collaboration between the server and query objects. In addition, we conduct extensive experiments to show that COMET substantially outperforms a conventional method in terms of query response time, bandwidth usage, and energy consumption.