A Discrete-Time Stochastic Traffic Assignment Model

A discrete time stochastic traffic assignment model is proposed. The model provides a discrete time description of the variations of flows on a road network during a day or a peak period. The congestion effect at links and link junctions are taken into account. The first in first out principle is enforced on all links at all periods of the day. A stochastic user equilibrium assignment is achieved when the tripmaker is unable to find better travel alternatives. A computational procedure is also presented.

Direct computing methods for turn flows in traffic assignment

Two methods based on a slight modification of the regular traffic assignmentalgorithms are proposed to directly compute turn flows instead of estimating them from link flows orobtaining them by expanding the networks. The first one is designed on the path-turn incidencerelationship, and it is similar to the computational procedure of link flows. It applies to thetraffic assignment algorithms that can provide detailed path structures. The second utilizes thelink-turn incidence relationship and the conservation of flow on links, a law deriving from thisrelationship. It is actually an improved version of Dial's logit assignment algorithm. The proposedapproaches can avoid the shortcomings both of the estimation methods, e. g. Furness's model andFrator's model, and of the network-expanding method in precision, stability and computation scale.Finally, they are validated by numerical examples.

Lazy loading algorithm for traffic assignment of road networks under fixed charge condition

The measures of path charge are important considerations in traffic assignment of road networks. Factors, such as travel time, fixed charge and traffic congestion which affect road users＇ choices of trip paths, are analyzed. Travelers usually decide their trip paths based on their personal habits, preferences and the information at hand. By considering both deterministic and stochastic factors which affect the value of time （VOT） during the process of path choosing, a variational inequality model is proposed to describe the problem of traffic assignment. A lazy loading algorithm for traffic assignment is designed to solve the proposed model, and the calculation steps are given. Numerical experiment results show that compared with the all-or-nothing assignment, the proposed model and the algorithm can provide more optimal traffic assignments for road networks. The results of this study can be used to optimize traffic planning and management.

Research on traffic congestion mechanism and countermeasures based on dynamic traffic assignment

Traffic congestion is widely distributed around a network. Generally, to analyze traffic congestion, static traffic capacity is adopted. But dynamic characteristics must be studied because congestion is a dynamic process. A Dynamic Traffic Assignment modeling fundamental combined with an urban congestion analysis method is studied in this paper. Three methods are based on congestion analysis, and the stochastic user optimal DTA models are especially considered. Correspondingly, a dynamic system optimal model is suggested for responding congestion countermeasures and an ideal user optimal model for predicted congestion countermeasure respectively.

Air Route Network Generation Based on Traffic Assignment

Air route network is the carrier of air traffic flow,and traffic assignment is a method to verify the rationality of air route network structure.Therefore,air route network generation based on traffic assignment has been becoming the research focus of airspace programming technology.Based on link prediction technology and optimization theory,a bi-level programming model is established in the paper.The model includes an upper level of air route network generation model and a lower level of traffic assignment model.The air route network structure generation incorporates network topology generation algorithm based on link prediction technology and optimal path search algorithm based on preference,and the traffic assignment adopts NSGA-Ⅲalgorithm.Based on the Python platform NetworkX complex network analysis library,a network of 57 airports,383 nodes,and 635 segments within China Airspace Beijing and Shanghai Flight Information Regions and 187975 sorties of traffic are used to simulate the bilevel model.Compared with the existing air route network,the proposed air route network can decrease the cost by 50.624%,lower the flight conflict coefficient by 33.564%,and reduce dynamic non-linear coefficient by 7.830%.

Traffic Assignment Forecast Model Research in ITS

As an important role in the development of ITS, traffic assignment forecast is always the research focus. Based on the analysis of classic traffic assignment forecast models, an improved traffic assignment forecast model, multi-ways probability and capacity constraint (MPCC) is presented. Using the new traffic as- signment forecast model to forecast the traffic volume will improve the rationality and veracity of traffic as- signment forecast.

A Trip-Chain Based User Equilibrium Traffic Assignment Model with Flexible Activities Scheduling Order

This study developed a user equilibrium traffic assignment model based on trip-chains with flexible activity scheduling order and derived the corresponding optimality conditions. We based on the gradient projection method to develop a solution algorithm, the accuracy of which was verified using the test network of UTown. This model could be used to estimate the transportation demands with and without activities scheduling restriction between OD （origin-destination） pairs based on trip-chains, as well as based on trips. Thus, the proposed model is more generalization than conventional trip based or trip-chain based traffic assignment models.

A Temporal Domain Decomposition Algorithmic Scheme for Large-Scale Dynamic Traffic Assignment

With emergent interest of Simulation-Based Dynamic Traffic Assignment(SBDTA)in the field of transportation network modeling,deployment of SBDTA models for traffic operations and transportation planning have increased significantly in recent years.In parallel,research and development of innovative approaches of the SBDTA model have enhanced the quality of both the assignment component,i.e,improvement of convergence quality of the Dynamic User Equilibrium(DUE)problem,and the traffic simulation element.However,computational requirement remains to be one of the great challenges for DTA implementations on large-scale networks with a long analysis period.This paper presents a temporal decomposition scheme for large spatial-and temporal-scale dynamic traffic assignment,in which the entire analysis period is divided into Epochs.Vehicle assignment is performed sequentially in each Epoch,thus improving the model scalability and confining the peak run-time memory requirement regardless of the total analysis period.A proposed self-turning scheme adaptively searches for the run-time-optimal Epoch setting during iterations regardless of the characteristics of the modeled network.Extensive numerical experiments confirm the promising performance of the proposed algorithmic schemes.

Bus frequency optimization in a large-scale multi-modal transportation system:integrating 3D-MFD and dynamic traffic assignment

A properly designed public transport system is expected to improve traffic efficiency.A high-frequency bus service would decrease the waiting time for passengers,but the interaction between buses and cars might result in more serious congestion.On the other hand,a low-frequency bus service would increase the waiting time for passengers and would not reduce the use of private cars.It is important to strike a balance between high and low frequencies in order to minimize the total delays for all road users.It is critical to formulate the impacts of bus frequency on congestion dynamics and mode choices.However,as far as the authors know,most proposed bus frequency optimization formulations are based on static demand and the Bureau of Public Roads function,and do not properly consider the congestion dynamics and their impacts on mode choices.To fill this gap,this paper proposes a bi-level optimization model.A three-dimensional Macroscopic Fundamental Diagram based modeling approach is developed to capture the bi-modal congestion dynamics.A variational inequality model for the user equilibrium in mode choices is presented and solved using a double projection algorithm.A surrogate model-based algorithm is used to solve the bi-level programming problem.

A topology-based bounded rationality day-to-day traffic assignment model

This paper analyzes the day-to-day adjustment process of users’behaviors in a transport network which is affected by relevant alterations such as disruptions due to critical events which cause the impossibility to use one or more links.For representing the progressive adjustment of the flows on the network to reach a new equilibrium,a dayto-day discrete-time model is proposed,based on the idea that people are bounded rational in their choices,i.e.they often do not behave according to the optimal solution but they accept solutions they consider satisfying.Users,in their choice process,are influenced by the topological similarity between the route they are currently using and others.This means that they tend to prefer the solutions that are more similar to the one they are already using.In parallel,users exhibit a myopic behavior,i.e.,they tend to overestimate the goodness of a route if,when using it,they suddenly experience a significant reduction in travel time compared to what they are used to.In the paper it is shown that such route choice behaviour implies that the steady state of the system corresponds to a Bounded Rational User Equilibrium,i.e.,a state that does not diverge from the user equilibrium more than a certain value which increases when the relative importance given to the topological similarity grows.The model also assumes that these biases vanish,at least with respect to those routes that are most frequently used by users,after a sufficient amount of time.Under certain conditions,it is then shown that the steady state can eventually collapse into a User Equilibrium.The effectiveness of the proposed model is assessed via simulation results in which two test networks are analyzed in detail to show the evolution of the users’behaviour in a transport network after a disruption.

Behaviours in a dynamical model of traffic assignment with elastic demand

This paper investigates the dynamical behaviour of network traffic flow. Assume that trip rates may be influenced by the level of service on the network and travellers are willing to take a faster route. A discrete dynamical model for the day-to-day adjustment process of route choice is presented. The model is then applied to a simple network for analysing the day-to-day behaviours of network flow. It finds that equilibrium is arrived if network flow consists of travellers not very sensitive to the differences of travel cost. Oscillations and chaos of network traffic flow are also found when travellers are sensitive to the travel cost and travel demand in a simple network.

A Skew Gradient-Based Newton Method for Traffic Assignment with Side Constraints

In this paper we describe how the capacitated user equilibrium can be approximated by sequential uncapacitated models by the use of a penalty function. The efficiency of the method is governed by the algorithmic performance of the uncapacitated model. A skew gradient-based Newton method is used to solve the capacitated user equilibrium within the feasible region of path flows. In the path-flow region, the straight gradient is defined as the derivative of the objective function with respect to the flow of the corresponding path, while the skew gradient is defined for each particular origin destination pair and is characterized by the average cost of all the paths for that pair. Instead of movement of flow toward the shortest path, in the equilibration procedure path flows below the average decrease and path flows above the average increase. The characteristics of the Newton method with the column generation procedure are combined to achieve the efficient determination of the equilibrium point. Numerical experiments demonstrate the excellent performance of the proposed method and highlight its potential applications.

Modified origin-based algorithm for traffic equilibrium assignment problems

Key tactics of origin-based user equilibrium (OUE) algorithm was studied,which involved the algorithm procedure and several implementation issues.To speed up the convergence,update policies of flows,costs and bushes were proposed.The methods of step-size searching and bush construction are proved to be practical.The modified OUE algorithm procedure was also optimized to take the advantage of multi-thread process.Convergence performances were compared with those of other algorithms by different sizes of urban transportation networks.The result shows this modified OUE algorithm is more efficient and consumes less time to achieve the reasonable relative gap in practical applications.

Simulation model based on Monte Carlo method for traffic assignment in local area road network

For a local area road network,the available traffic data of traveling are the flow volumes in the key intersections,not the complete OD matrix.Considering the circumstance characteristic and the data availability of a local area road network,a new model for traffic assignment based on Monte Carlo simulation of intersection turning movement is provided in this paper.For good stability in temporal sequence,turning ratio is adopted as the important parameter of this model.The formulation for local area road network assignment problems is proposed on the assumption of random turning behavior.The traffic assignment model based on the Monte Carlo method has been used in traffic analysis for an actual urban road network.The results comparing surveying traffic flow data and determining flow data by the previous model verify the applicability and validity of the proposed methodology.

Trasfugen:Traffic assignment of urban network by an approximation fuzzy genetic algorithm

This paper proposes the Trasfugen method for traffic assignment aimed at solving the user equilibrium problem.To this end,the method makes use of a genetic algorithm.A fuzzy system is proposed for controlling the mutation and crossover rates of the genetic algorithm,and the corrective strategy is exploited for handling the equilibrium problem constraints.In the model,an approximation algorithm is proposed for obtaining the paths between the origin–destination pairs in the demand matrix.Unlike the traditional deterministic algorithm that has exponential time complexity,this approximation algorithm has polynomial time complexity and is executed much faster.Afterward,the Trasfugen method is applied to the urban network of Tehran metropolitan and the efficiency is investigated.Upon comparing the results obtained from the proposed model with those obtained from the conventional traffic assignment method,namely,the Frank–Wolfe method;it is shown that the proposed algorithm,while acting worse during the initial iterations,achieves better results in the subsequent iterations.Moreover,it prevents the occurrence of local optimal points as well as early/premature convergence,thus producing better results than the Frank–Wolfe algorithm.

An ADMM-based parallel algorithm for solving traffic assignment problem with elastic demand

Efficiently solving the user equilibrium traffic assignment problem with elastic demand(UE-TAPED)for transportation networks is a critical problem for transportation studies.Most existing UE-TAPED algorithms are designed using a sequential computing scheme,which cannot take advantage of advanced parallel computing power.Therefore,this study focuses on model decomposition and parallelization,proposing an origin-based formulation for UE-TAPED and proving an equivalent reformulation of the original problem.Furthermore,the alternative direction method of multipliers(ADMM)is employed to decompose the original problem into independent link-based subproblems,which can solve large-scale problems with small storage space.In addition,to enhance the efficiency of our algorithm,the parallel computing technology with optimal parallel computing schedule is implemented to solve the link-based subproblems.Numerical experiments are performed to validate the computation efficiency of the proposed parallel algorithm.

Dynamical evolution processes of traffic flow and travel cost in urban transportation networks

Considering such a fact that travellers dynamically adjust their routes and the resultant link traffic flows in a network evolve over time, this paper proposes a dynamical evolutionary model of the traffic assignment problem with endogenous origin-destination （OD） demands. The model＇s stability is analysed and the resultant user equilibrium （UE） state is shown to be stable under certain conditions. Numerical results in a grid network indicate that the model can generate convergent flow patterns and finally terminates at the UE state. Impacts by the parameters associated with OD demand function and link cost function are also investigated.

Integration control for traffic corridors considering guidance information

The problem of designing integration traffic strategies for traffic corridors with the use of ramp metering, speed limit, and route guidance is considered in this paper. As an improvement to the previous work, the presented approach has the following five features： 1） modeling traffic flow to analyze traffic characteristics under the influence of variable speed limit, on-ramp metering and guidance information; 2） building a hierarchy model to realize the integration design of traffic control and route guidance in traffic corridors; 3） devising a multi-class analytical dynamic traffic assignment （DTA） model for traffic corridors, where not only the route choice process will be different for each user-class, but also the traffic flow operations are user-class specific because the travel time characteristic for each user-class is considered; 4） predicting route choice probabilities adaptively with real-time traffic conditions and route choice behaviors corresponding to variant users, rather than assuming as pre-determined; and 5） suggesting a numerical solution algorithm of the hierarchy model presented in this paper based on the modified algorithm of iterative optimization assignment （IOA）. Preliminary numerical test demonstrates the potential of the developed model and algorithm for integration corridor control.

Combinatorial Model Involving Mixed Deterministic Freight Volume Distribution and User's Equilibrium Assignment

Considering characteristics of Chinese urban mixed traffic,the author develops a combinatorial model involving the mixed deterministic traffic volume distribution and user's equilibrium (UE) assignment on the basis of symmetrical link travel time function (or deterrence).Its uniqueness and equivalance to the Wardropian principle of UE are also proved.Finally,we give the algorithm of model.

面向动态交通分配的城市道路网络分区研究

提出了城市道路网络的动态可分配性概念,以衡量对特定城市道路网络实施动态分配研究的有效性.并将这个概念用于面向动态交通分配的城市道路网络子区划分,考虑了道路网络的动态变化特性,不仅在空间上,也在时间上对道路网络进行了分区研究.该研究可为动态交通分配的建模研究提供合理的背景和对象.