Wei Hua Lin

Interests

Teaching

Transportation engineering, traffic flow theory, traffic operation, logistics, statistical analysis of transportation data, operations research and computer applications in transportation, and transportation network analysis.

Research

Traffic flow modeling, information technologies in transportation, transportation data analysis, transportation network, analysis and modeling, freeway incident management, application of advanced technologies in transit operations, and application of computer simulation to transportation analysis.

Courses

Scholarly Contributions

Journals/Publications

• Xue, Z., Lin, W., Miao, L., & Zhang, C. (2014). Local container drayage problem with tractor and trailer operating in separable mode. Flexible Services and Manufacturing Journal, 1-20.
  More info

  Abstract: In recent years, the Local Container Drayage Problem (LCDP) has received lots of studies in research as part of container transportation. This paper examines the LCDP under a special operation mode in which tractors and trailers can be separated, i.e., tractors can be assigned to a new task at another location while trailers are waiting for packing or unpacking. The problem is formulated as a vehicle routing and scheduling problem with temporal constraints. The resulting formulation can be used to solve small-scale problems. For large-scale problems, we develop a max-min Ant colony optimization algorithm to reduce the computation time. Numerical experiments with randomly generated instances are performed to demonstrate the performance of the algorithm. © 2014 Springer Science+Business Media New York.
• Xue, Z., Zhang, C., Lin, W., Miao, L., & Yang, P. (2014). A tabu search heuristic for the local container drayage problem under a new operation mode. Transportation Research Part E: Logistics and Transportation Review, 62, 136-150.
  More info

  Abstract: This paper examines the Local Container Drayage Problem (LCDP) under an operation mode in which a tractor can be detached from its companion trailer and assigned to a new task. We have incorporated a set of temporal constraints into the classical VRP to realize this operation by utilizing the idle time available to tractors and coordinating the empty containers moving between customers. A tabu search algorithm is proposed. Some numerical experiments are conducted to assess the performance of the proposed algorithm, quantify the benefit of the new operation mode, and identify the conditions under which the mode is effective. © 2013 Elsevier Ltd.
• Chen, C., Liu, Z., Lin, W., Shuangshuang, L. i., & Wang, K. (2013). Distributed modeling in a mapreduce framework for data-driven traffic flow forecasting. IEEE Transactions on Intelligent Transportation Systems, 14(1), 22-33.
  More info

  Abstract: With the availability of increasingly more new data sources collected for transportation in recent years, the computational effort for traffic flow forecasting in standalone modes has become increasingly demanding for large-scale networks. Distributed modeling strategies can be utilized to reduce the computational effort. In this paper, we present a MapReduce-based approach to processing distributed data to design a MapReduce framework of a traffic forecasting system, including its system architecture and data-processing algorithms. The work presented here can be applied to many traffic forecasting systems with models requiring a learning process (e.g., the neural network approach). We show that the learning process of the forecasting model under our framework can be accelerated from a computational perspective. Meanwhile, model fusion, which is the key problem of distributed modeling, is explicitly treated in this paper to enhance the capability of the forecasting system in data processing and storage. © 2000-2011 IEEE.
• Cheng, Y., Tan, J., & Lin, W. (2013). Allocating the cost of empty railcar miles in a dynamic railroad network. International Journal of Shipping and Transport Logistics, 5(3), 350-366.
  More info

  Abstract: In a multi-level railcar system, the formation of coalitions among railcar companies can potentially lead to a reduction in the total empty mile cost, an important part of the variable cost of the railcar system. In order to maintain a sustainable coalition, it is important to ensure that the costs incurred in the coalition will be fairly allocated to participating companies in the coalition. This paper proposes a cost allocation scheme based on game theory that allocates the cost of empty car miles to participating companies in a coalition for a railcar system. The method can ensure fairness and enhance stability of a coalition since it explicitly considers the level of contribution from each company in the coalition. The properties important for fairness in cost allocation and stability for the coalition are discussed. We have also demonstrated in the paper that the proposed cost allocation scheme can be coupled with a generalised optimisation model for empty car distribution in a dynamic railroad network. Copyright © 2013 Inderscience Enterprises Ltd.
• Lei, C., Lin, W. H., & Miao, L. (2013). The stochastic emergency service vehicle re-routing problem. Proceedings of the 18th International Conference of Hong Kong Society for Transportation Studies, HKSTS 2013 - Travel Behaviour and Society, 625-632.
  More info

  Abstract: This paper considers the emergency service vehicle re-routing problem (ESVRP) under uncertainty. We develop a stochastic programming model for ESVRP, aiming at adjusting the original routing and scheduling plan to reposition ESVs when some ESVs in the fleet become temporarily unavailable in response to service calls. The purpose of the model is to optimize the system-wide performance throughout the planning horizon while treating both the service needs and the return times of "busy service vehicles" as random variables. A comparative analysis of different strategies in dealing with the busy ESVs is performed to assess the performance of the proposed model. The results indicate that our modelling approach is effective in handling uncertainty.
• Lei, C., Lin, W., Miao, L., & Mingyao, Q. i. (2013). Stochastic mobile facility routing and scheduling problem. IEEE Conference on Intelligent Transportation Systems, Proceedings, ITSC, 1823-1828.
  More info

  Abstract: We consider the mobile facility routing and scheduling problem with stochastic demand (MFRSPSD). MFRSPSD simultaneously determines the route and schedule of a fleet of mobile facilities which serve customers with uncertain demand in order to minimize the total cost generated over the planning horizon. The problem is formulated as a two-stage stochastic programming model, in which the first stage decision deals with the temporal and spatial movement of the MFs and the second stage handles how MFs serve customer demands. An algorithm based on the multicut version of L-shaped method is developed. The computational results show that the algorithm yields high quality upper and lower bounds within reasonable computation time for medium scale problems. © 2013 IEEE.
• Lo, H. K., Kun, A. n., & Lin, W. (2013). Ferry service network design under demand uncertainty. Transportation Research Part E: Logistics and Transportation Review, 59, 48-70.
  More info

  Abstract: This paper develops a formulation for ferry service network design with stochastic demand via the notion of service reliability (SR). The problem is formulated as a two-phase stochastic program in which the schedule of regular and ad hoc services are derived sequentially. An example is presented to illustrate the formulation. We then apply the proposed method to the case of ferry network design in Hong Kong. In terms of solution quality and computational efficiency, the SR-based approach shows promising results as compared with existing methods. Moreover, the approach leads to substantial cost savings as compared with deterministic methods under demand uncertainty. © 2013 Elsevier Ltd.
• Tong, D., Lin, W., & Stein, A. (2013). Integrating the Directional Effect of Traffic into Geostatistical Approaches for Travel Time Estimation. International Journal of Intelligent Transportation Systems Research, 11(3), 101-112.
  More info

  Abstract: With the direct linkage to a travel map system, geostatistical techniques have been recently adopted for urban travel time estimation. Some important traffic characteristics of urban transportation networks, however, have not been adequately addressed in these studies. As an improvement over the existing studies, this study incorporates the directional effect of traffic into several commonly used geostatistical models for travel time estimation. We show that model performance can be significantly enhanced when flow specific properties are explicitly considered in constructing the associated interpolation models. The developed methodology is applied to a set of traffic data collected in the city of Tucson, Arizona during the rush hours. Results demonstrate an average of 20 % reduction in RMSE compared with those by the traditional approaches. © 2013 Springer Science+Business Media New York.
• Xue, Z., Zhang, C., Miao, L., & Lin, W. (2013). An ant colony algorithm for yard truck scheduling and yard location assignment problems with precedence constraints. Journal of Systems Science and Systems Engineering, 22(1), 21-37.
  More info

  Abstract: This paper examines the yard truck scheduling, the yard location assignment for discharging containers, and the quay crane scheduling in container terminals. Taking into account the practical situation, we paid special attention to the loading and discharging precedence relationships between containers in the quay crane operations. A Mixed Integer Program (MIP) model is constructed, and a two-stage heuristic algorithm is proposed. In the first stage an Ant Colony Optimization (ACO) algorithm is employed to generate the yard location assignment for discharging containers. In the second stage, the integration of the yard truck scheduling and the quay crane scheduling is a flexible job shop problem, and an efficient greedy algorithm and a local search algorithm are proposed. Extensive numerical experiments are conducted to test the performance of the proposed algorithms. © 2013 Systems Engineering Society of China and Springer-Verlag Berlin Heidelberg.
• Mingyao, Q. i., Lin, W., Nan, L. i., & Miao, L. (2012). A spatiotemporal partitioning approach for large-scale vehicle routing problems with time windows. Transportation Research Part E: Logistics and Transportation Review, 48(1), 248-257.
  More info

  Abstract: For VRP with time windows (VRPTW) solved by conventional cluster-first and route-second approach, temporal information is usually considered with vehicle routing but ignored in the process of clustering. We propose an alternative approach based on spatiotemporal partitioning to solving a large-scale VRPTW, considering jointly the temporal and spatial information for vehicle routing. A spatiotemporal representation for the VRPTW is presented that measures the spatiotemporal distance between two customers. The resulting formulation is then solved by a genetic algorithm developed for k-medoid clustering of large-scale customers based on the spatiotemporal distance. The proposed approach showed promise in handling large scale networks. © 2011 Elsevier Ltd.
• Wangtu, X. u., Miao, L., & Lin, W. (2012). Stochastic user equilibrium assignment in schedule-based transit networks with capacity constraints. Discrete Dynamics in Nature and Society, 2012.
  More info

  Abstract: This paper proposes a stochastic user equilibrium (SUE) assignment model for a schedule-based transit network with capacity constraint. We consider a situation in which passengers do not have the full knowledge about the condition of the network and select paths that minimize a generalized cost function encompassing five components: (1) ride time, which is composed of in-vehicle and waiting times, (2) overload delay, (3) fare, (4) transfer constraints, and (5) departure time difference. We split passenger demands among connections which are the space-time paths between OD pairs of the network. All transit vehicles have a fixed capacity and operate according to some preset timetables. When the capacity constraint of the transit line segment is reached, we show that the Lagrange multipliers of the mathematical programming problem are equivalent to the equilibrium passenger overload delay in the congested transit network. The proposed model can simultaneously predict how passengers choose their transit vehicles to minimize their travel costs and estimate the associated costs in a schedule-based congested transit network. A numerical example is used to illustrate the performance of the proposed model. © 2012 Wangtu Xu et al.
• Lin, W., & Tong, D. (2011). Vehicle re-identification with dynamic time windows for vehicle passage time estimation. IEEE Transactions on Intelligent Transportation Systems, 12(4), 1057-1063.
  More info

  Abstract: A simple method for vehicle re-identification to generate vehicle passage times with loop data is developed. The method departs from other existing methods for vehicle passage time estimation: 1) It handles vehicle signatures one at a time and evaluates each vehicle observed only once. 2) The commonly used prespecified time window is replaced by a dynamic list of vehicles to be matched. 3) Vehicle matching is based on a combined estimation model that integrates spot traffic data with spatial vehicle data. The performance of the algorithm was tested with field data. Furthermore, to examine the effect of some of the assumptions on the performance of the algorithm, we compared the result with that obtained from an offline optimization model based on a spatial constraint that considers as many vehicles as possible for matching. The proposed method is particularly suitable for real-time applications since it can be easily implemented with little calibration effort and is computationally efficient. © 2011 IEEE.
• Lin, W., Lo, H. K., & Xiao, L. (2011). A quasi-dynamic robust control scheme for signalized intersections. Journal of Intelligent Transportation Systems: Technology, Planning, and Operations, 15(4), 223-233.
  More info

  Abstract: Conventional vehicle-actuated traffic signal control attempts to achieve system optimum by ending a phase as soon as queues served during that phase vanish. In this article, the authors extend this logic to intersections where a stable cycle length is desirable (e.g., for signal coordination or other considerations). The proposed control scheme dynamically updates green allocation to keep queues on all approaches well balanced. Different from fully dynamic control strategies, the proposed quasi-dynamic scheme is based on a finite set of fixed timing plans with a common cycle length. The decision of switching from one plan to another is made at the beginning of each cycle based on the queue state in the previous cycle. Our experimental results showed that the performance of the proposed scheme is robust with respect to random fluctuation, systematic changes in demand, and input data quality. Although the proposed scheme does not attempt to minimize total system delay directly, it provides a good solution for reducing total system delay compared with the signal timing plan optimized for system delay. The preservation of a stable cycle length in the proposed signal timing plan has made it possible to incorporate the proposed scheme into the development of control strategies for an arterial where signal coordination is essential to the performance of the system. © 2011 Copyright Taylor and Francis Group, LLC.
• Zhang, J., Wang, F., Wang, K., Lin, W., Xin, X. u., & Chen, C. (2011). Data-driven intelligent transportation systems: A survey. IEEE Transactions on Intelligent Transportation Systems, 12(4), 1624-1639.
  More info

  Abstract: For the last two decades, intelligent transportation systems (ITS) have emerged as an efficient way of improving the performance of transportation systems, enhancing travel security, and providing more choices to travelers. A significant change in ITS in recent years is that much more data are collected from a variety of sources and can be processed into various forms for different stakeholders. The availability of a large amount of data can potentially lead to a revolution in ITS development, changing an ITS from a conventional technology-driven system into a more powerful multifunctional data-driven intelligent transportation system (D2ITS): a system that is vision, multisource, and learning algorithm driven to optimize its performance. Furthermore, D2ITS is trending to become a privacy-aware people-centric more intelligent system. In this paper, we provide a survey on the development of D2ITS, discussing the functionality of its key components and some deployment issues associated with D2ITS. Future research directions for the development of D2ITS is also presented. © 2011 IEEE.
• Gan, M., & Lin, W. (2010). The effect of demand representation on locating facilities in a supply chain network. Proceedings of 2010 IEEE International Conference on Service Operations and Logistics, and Informatics, SOLI 2010, 189-194.
  More info

  Abstract: The objectives of a typical facility location problem is either to maximize the coverage with a given number of facilities or to minimize the number of facilities used to cover a given area. In recent years, it has been found that how demand is characterized in a facility location model can significantly affect the performance of facility location models. In a supply chain network the goal is often to maximize the demand coverage and minimize the total costs (construction, transaction, operation, etc.) subject to a set of constraints. In this paper, we explored the importance of demand representation in the context of a supply chain network and examined how a realistic representation of demand in a supply chain network would affect the network design. We fIrSt analyzed the general definition and characteristics of the facility location problem in a supply chain. We then examined the various objectives and constraints associated with the demand representation and formulated a multi-objectives model to address the facility location problem in a supply chain network. The overlap function of ArcGIS 9.3 was utilized and a solution procedure to the proposed problem was developed. Finally a numerical example was generated to examine the performance of the proposed model and its solution algorithm. © 2010 IEEE.
• Lin, W., & Liu, H. (2010). Enhancing realism in modeling merge junctions in analytical models for system-optimal dynamic traffic assignment. IEEE Transactions on Intelligent Transportation Systems, 11(4), 838-845.
  More info

  Abstract: The existing analytical system-optimal dynamic traffic assignment (SO-DTA) model formulated with the linear programming (LP) approach usually assumes system control over vehicles in the entire network. This property would give rise to unreasonable priorities at merge junctions that are sometimes physically impossible to realize for the given roadway configuration. In this paper, we demonstrate that models with and without considering the merge-priority ratio would exhibit very different traffic patterns and route-choice behavior. To realistically model traffic flow on a transportation network, one should properly distinguish the level of control by drivers, roadway geometry, and system providers. This paper also attempts to develop an LP module that explicitly considers the merge-priority ratio of a merge junction and can potentially be incorporated into the existing LP formulation of the SO-DTA problem based on the cell-transmission model. By more realistically modelling the behavior of vehicles at merge junctions, the obtained solution can be used as a benchmark to compare control strategies developed without explicitly considering the merge-priority ratio at merge junctions or strategies developed with heuristic approaches. © 2006 IEEE.
• Qing, H. e., Lin, W., Liu, H., & Head, K. L. (2010). Heuristic algorithms to solve 0-1 mixed integer LP formulations for traffic signal control problems. Proceedings of 2010 IEEE International Conference on Service Operations and Logistics, and Informatics, SOLI 2010, 118-124.
  More info

  Abstract: In this paper, three heuristic solution algorithms, (the Dive-and-Fix method, the Ratio-cluster method, and the Cumulative-departure method) are specially designed to solve the traffic signal control problem formulated as a 0-1 mixedinteger linear programming problem with cell transmission model. These three solution algorithms are based on two fundamental approaches. First, the 0-1 mixed-integer linear program is solved via linear relaxation (LR). Second, the noninteger solutions obtained from the LR are converted into the integer solutions by taking advantage of the underlying physical mechanism embedded in the LR solutions that lead to the optimal signal control. In particular, proportional capacities for different approaches and the cumulative exit flow at each intersection obtained from the LR solutions are utilized to determine green time allocation for each approach. It is demonstrated that the near-optimal solutions obtained with these algorithms are very close to the optimal solutions under both uncongested and congested traffic conditions. © 2010 IEEE.
• Tong, D., Lin, W., MacK, J., & Mueller, D. (2010). Accessibility-based multicriteria analysis for facility siting. Transportation Research Record, 128-137.
  More info

  Abstract: Maximizing accessibility is often an important consideration in the location of a facility. This paper describes the development of a planning procedure based on a geographic information system (GIS) to assist decision makers in site selection when various accessibility criteria are considered. The procedure is illustrated in the context of siting a new women's and children's community center in Tucson, Arizona. First, suitable sites are identified as candidates on the basis of constraints related to transportation, land use, zoning, and so forth. Then a GIS-based decision support system is designed to assess the optimality of the candidate sites on the basis of accessibility by different population groups modeled, with the use of a multiobjective mathematical programming approach. Although this analysis focuses on a single facility, the methodology discussed, including the use of visual assessment tools and the development of the optimization model, can be used for multiple site selection and easily extended to other applications in which accessibility is a key component.
• Lin, W., & Lo, H. K. (2009). Investigating Braess' paradox with time-dependent queues. Transportation Science, 43(1), 117-126.
  More info

  Abstract: In the 1960s, Braess showed that the overall system performance of a transportation network can be degraded when a new link is added to the network, given that travelers choose their routes based on the user equilibrium (UE) principle. This phenomenon is often referred to as Braess' paradox (BP). The original five-link BP network has been studied extensively with static link performance functions. In this paper, we revisit the original BP network with a dynamic point-queue model and examine whether the results from the static model would hold for the case with time-dependent queues. For this purpose, we solve the BP problem with the consideration of dynamic queuing that leads the system to a steady state while satisfying the dynamic user equilibrium (DUE) condition at every instant. Our results indicate that the locations of congestion, or "hot spots," of the system are sensitive to the capacity of each link in an intricate manner. The "surprising result" reported in previous studies with link performance functions, that a system can spontaneously grow out of Braess' paradox if the demand is sufficiently high, does not occur with time-dependent queues. Instead, we show that queues in different stages have different impacts on the system performance. The implication of this result is discussed in the context of developing proactive dynamic traffic control strategies that can eliminate the negative impact of BP while keeping the system operating at the DUE condition. Even though this study focuses on the original five-link network, the results illustrate the potential pitfalls of extending insights developed from a static framework for dynamic traffic and the importance of studying the problem with a dynamic framework for real-time traffic control. © 2009 INFORMS.
• Liu, H., Balke, K. N., & Lin, W. (2008). A reverse causal-effect modeling approach for signal control of an oversaturated intersection. Transportation Research Part C: Emerging Technologies, 16(6), 742-754.
  More info

  Abstract: A novel approach is presented in which signalized intersections are treated as normal highway bottlenecks for improved computational efficiency. It is unique in two ways. First, it treats the signalized intersections as common freeway bottlenecks by a reversed cause and effect modeling approach. Both traffic arrivals and departures are modeled by smooth continuous functions of time as if there were no interruptions to traffic flows from signals. The use of smooth continuous functions for departure curves instead of commonly used step functions makes it easy to apply differential calculus in optimization and future extension to a system of intersections. Second, a dynamic linear programming (LP) model is then developed to maximize the total vehicular output from the intersection during the entire period of congestion subject to prevailing capacity and other operational constraints. The continuous optimal departure flow rate (the effect) is then converted to signal timing parameters (the cause) that can be readily implemented. Two numerical examples are presented to demonstrate the properties of the proposed algorithm and examine its performance. © 2008 Elsevier Ltd. All rights reserved.
• Liu, H., Lin, W., & Tan, C. (2007). Operational strategy for advanced vehicle location system-based transit signal priority. Journal of Transportation Engineering, 133(9), 513-522.
  More info

  Abstract: Future deployments of transit signal priority (TSP) in the United States depend largely on improving TSP strategies to better accommodate transit vehicles while at the same time minimizing the negative impacts on the vehicles of the nonprioritized approaches. Advanced vehicle location (AVL) technology holds great potential in this regard. This paper develops a methodology that incorporates the predicted bus arrival time information into an AVL based TSP system to improve its performance. It is demonstrated analytically that the time to trigger the traffic signal for priority operation, especially Early Green, is of particular importance to both transit and passenger vehicles. A theoretical model is developed to identify the optimal time to place a priority call based on the predicted bus arrival time information. A simulation analysis is conducted to verify the theoretical approach and further identify the optimal call-time points for general cases. The research is focused on operation of TSP under moderately congested and congested traffic conditions wherein the concern about the adverse impact of TSP exists. It shows that in general, starting the priority operation when the bus is about 20-30s away from the intersection produces good results for both bus and general traffic. The findings of the research can be easily integrated into an AVL based TSP system and may potentially enhance the performance of such a system. © 2007 ASCE.
• Li, L., Li, L., Lin, W. -., Lin, W. -., Liu, H., & Liu, H. (2006). Type-2 fuzzy logic approach for short-term traffic forecasting. IEE Proceedings: Intelligent Transport Systems, 153(1), 33-40.
  More info

  Abstract: The performance of many components in intelligent transportation systems depends heavily on the quality of short-term traffic forecasts. We propose a new method for forecasting traffic based on type-2 fuzzy logic. Type-2 fuzzy logic is powerful in handling uncertainties, including uncertainties in measurements and data used to calibrate the parameters. In our formulation, the value of a membership function corresponding to a particular traffic state is no longer a crisp value. Rather, it is associated with a range of values that can be characterised by a function that reflects the level of uncertainty. Day-to-day traffic information is combined with real-time traffic information to construct fuzzy rules. The performance of the prediction procedure based on type-2 fuzzy logic is encouraging. The mean relative error is in the neighbourhood of 12 for occupancies and 5 for flows. A distinct advantage of a type-2 fuzzy logic-based traffic forecasting approach is that it can produce prediction intervals as a by-product of the fuzzy reduction process. Another desirable property of the proposed model is that the fuzzy engine formulated is usually tractable at every step, making it easy to incorporate site-specific information into the model-building process to obtain more accurate results.
• Lin, W., Kulkarni, A., & Mirchandani, P. (2006). Response to "comment on 'short-term arterial travel time prediction for advanced traveler information systems' by Wei-Hua Lin, Amit Kulkarni, and Pitu Mirchandani. Journal of Intelligent Transportation Systems: Technology, Planning, and Operations, 10(1), 45-47.
  More info

  Abstract: The discussion given in this note is in response to the comments by the discussant, T. Tsekeris.
• Cheng, Y., & Lin, W. (2005). Comparison of methods for allocating costs of empty railcar movements in a railcar pooling system. Transportation Research Record, 88-95.
  More info

  Abstract: Allocating the cost of empty railcar miles to partners in a railcar pooling system is an important pricing problem in railway management. Recently, the authors of this paper proposed a cost allocation scheme for empty railcar movements based on game theory that explicitly considers the level of participation and contribution from each partner, the costs generated before and after cooperation, and the overall benefit obtained by each partner because of cooperation. This paper compares the performance of the model with three other cost allocation models with respect to fairness, stability, and computational efficiency. The comparison is made with two scenarios adapted from examples documented in the literature. The results indicate that the cost allocation scheme based on game theory outperforms other methods in ensuring fairness and enhancing stability in a coalition. Most remarkably, it yields reasonable results even in situations in which other models behave poorly. Computationally, it is manageable for practical problems.
• Lefei, L. i., Lin, W., & Liu, H. (2005). Traffic signal priority/preemption control with colored petri nets. IEEE Conference on Intelligent Transportation Systems, Proceedings, ITSC, 2005, 694-699.
  More info

  Abstract: A Colored Petri Net (CPN) model for traffic signal priority/preemption is described. The model incorporates the priority/preemption request of transit vehicles into traffic signal control. Compared with 'uncolored' Petri Nets (PN), CPN provides a broader modeling capability for traffic signal priority control. A simple priority evaluation procedure is proposed to provide different priorities to multiple priority requests. An example for the queue jump phase modeled with CPN is presented. © 2005 IEEE.
• Lin, W., & Liu, H. (2005). A mathematical programming module for merge control in system optimal dynamic traffic assignment. IEEE Conference on Intelligent Transportation Systems, Proceedings, ITSC, 2005, 103-108.
  More info

  Abstract: This paper attempts to enhance the existing linear programming (LP) formulation of the system optimal dynamic traffic assignment SO-DTA problem by treating the priority ratio of a merge junction with a linear programming module equivalent to the non-linear merge component in the cell transmission model. The proposed formulation preserves the proper merge priority rule and can be readily embedded into an LP formulation of the SO-DTA problem for a single destination. It is capable of distinguishing control governed by the roadway geometry and control imposed by the system provider. The other contribution of the paper is that the model proposed also provides an alternative graphical interpretation of the merge rule described in the cell transmission model. © 2005 IEEE.
• Cheng, Y., & Lin, W. (2004). A network-based scheme for allocating the cost of empty railcar movements in railway systems. Conference Proceeding - IEEE International Conference on Networking, Sensing and Control, 2, 844-849.
  More info

  Abstract: In the freight industry, allocating the cost of empty miles of rail cars to partners in coalition is an important pricing problem. This paper proposes an empty car movement cost allocation scheme based on the game theory that explicitly considers the level of participation and contribution from each partner, the costs generated before and after cooperation, and the overall benefits obtained by each partner due to cooperation. Characterization of cost at each level of cooperation is considered based on the empty miles generated or reduced through cooperation. Compared with other existing models, the proposed cost allocation scheme consistently yields reasonable results, even under the situation in which other models behave poorly. We also show that the proposed pricing scheme can enhance the stability of a coalition such that the subgroup of a coalition will not be better off if the members of the subgroup choose to break away from the coalition.
• Lin, W., & Bertini, R. L. (2004). Modeling schedule recovery processes in transit operations for bus arrival time prediction. Journal of Advanced Transportation, 38(3), 347-365.
  More info

  Abstract: Many existing algorithms for bus arrival time prediction assume that buses travel at free-flow speed in the absence of congestion. As a result, delay incurred at one stop would propagate to downstream stops at the same magnitude. In reality, skilled bus operators often constantly adjust their speeds to keep their bus on schedule. This paper formulates a Markov chain model for bus arrival time prediction that explicitly captures the behavior of bus operators in actively pursuing schedule recovery. The model exhibits some desirable properties in capturing the schedule recovery process. It guarantees provision of the schedule information if the probability of recovering from the current schedule deviation is sufficiently high. The proposed model can be embedded into a transit arrival time estimation model for transit information systems that use both real-time and schedule information, It also has the potential to be used as a decision support tool to determine when dynamic or static information should be used.
• Lin, W., & Wang, C. (2004). An enhanced 0-1 mixed-integer LP formulation for traffic signal control. IEEE Transactions on Intelligent Transportation Systems, 5(4), 238-245.
  More info

  Abstract: An enhanced 0-1 mixed-integer linear programming formulation based on the cell-transmission model is proposed for the traffic signal optimization problem. This formulation has several features that are currently unavailable in other existing models developed with a similar approach, including the components for handling the number of stops, fixed or dynamic cycle length and splits, and lost time. The problem of unintended vehicle holding, which is common in analytical models, is explicitly treated. The formulation can be utilized in developing strategies for adaptive traffic-control systems. It can also be used as a benchmark for examining the convergence behavior of heuristic algorithms based on the genetic algorithm, fuzzy logic, neural networks, or other approaches that are commonly used in this field. The discussion of extending the proposed model to capture traffic signal preemption in the presence of emergency vehicles is given. In terms of computational efficiency, the proposed formulation has the least number of binary integers as compared with other existing formulations that were developed with the same approach.
• Lin, W., Dahlgren, J., & Huo, H. (2004). Enhancement of vehicle speed estimation with single loop detectors. Transportation Research Record, 147-152.
  More info

  Abstract: Traffic data from single loop detectors are a dominant data source widely used in traffic operation centers and traveler information systems. Speed estimation from single loop detectors is based mainly on occupancy data, a conversion factor from occupancy to density (which is related to vehicle length), and the assumed relationship between flow, speed, and density. The discrepancy between the speed estimated with single loops and the speed measured directly from double loops was investigated. It was found that the inaccuracy of speed estimation done with single loops was caused mainly by the irregular behavior of vehicle pace. Under congested or unstable traffic conditions, the distribution of vehicle pace within a given time interval often exhibits a large variance accompanied by a strong skewness. Accuracy in speed estimation can be improved by computing occupancy in a different way - by using median vehicle passage time over the detector - instead of mean vehicle passage time, often used in the conventional method. The performance of the enhanced speed estimation method is very encouraging. The use of the median vehicle passage time reduces the skewness of pace data.
• Lin, W., Kulkarni, A., & Mirchandani, P. (2004). Short-term arterial travel time prediction for advanced traveler information systems. Journal of Intelligent Transportation Systems: Technology, Planning, and Operations, 8(3), 143-154.
  More info

  Abstract: While vehicular flows on freeways are often treated as uninterrupted flows, flows on arterials are conceivably much more complicated because vehicles traveling on arterials are not only subject to queuing delay but also to signal delay. Prediction of travel time is potentially more challenging for arterials than for freeways. This article proposes a simple model for arterial travel time prediction. The proposed approach decomposes total delay on an arterial into link delay and intersection delay. Intersection delay in the context of arterial travel time prediction is very different from the average delay at an intersection. The proposed approach reduces the delay at each intersection, a non-negative continuous variable, into two distinctive states, a state of zero-delay and a state of nominal delay, coupled with a one-step transition matrix that relates the delay to a through vehicle at an intersection to its delay status at the adjacent upstream intersection. The parameters of the transition matrix are based on three key factors: the flow condition, the proportion of net inflows into the arterial from the cross streets, and the signal coordination level. Comparison of predicted delay with simulated delay indicates that the model can yield predictions with a reasonable degree of accuracy under various traffic conditions and signal coordination levels.
• Lin, W., & Lo, H. K. (2003). A theoretical probe of a German experiment on stationary moving traffic jams. Transportation Research Part B: Methodological, 37(3), 251-261.
  More info

  Abstract: Kerner and Rehborn (Phys.Rev.E 53 (2) (1996)) reported on the observation of two stationary moving jams that lasted for about an hour on a 13 km long German highway section. They attributed the phenomenon to intrinsic characteristics of traffic flow, something that would arise spontaneously within the traffic stream due to drivers' driving behavior. We show in this paper that these moving jams are not particularly peculiar but can be explained with the hydrodynamic theory of traffic flow, or the Lighthill-Whitham-Richards model, and the merge and diverge models in the cell transmission model. In fact, we demonstrate that this stationary jam phenomenon can be replicated with a simple two-wave velocity (or triangular) flow-density relationship in conjunction with the hydrodynamic theory. This finding provides some evidence to support that a triangular flow-density relationship is a good approximation of field observations and that a simple first-order hydrodynamic theory is capable of explaining complex traffic phenomenon. © 2003 Elsevier Science Ltd. All rights reserved.
• Lin, W. (2002). Quantifying delay reduction to buses with signal priority treatment in mixed-mode operation. Transportation Research Record, 100-106.
  More info

  Abstract: The benefits of the signal priority system to buses in terms of delay reduction in mixed-mode operation have been quantitatively assessed. Analytical expressions were derived to quantify the benefits. Delay reduction under a signal priority system is bounded by signal delay but independent of queuing delay; delay reduction has a high variance/mean ratio, which suggests that sufficient slack time should be built into a bus schedule to maintain reliable service, even for buses that receive priority treatment; the benefits are more significant for buses traveling on cross streets than for those on main streets because the red phase for the cross street typically is much longer than the minimum red required for pedestrian crossing.
• Lin, W., & Padmanabhan, V. (2002). Simple procedure for creating digitized bus route information for intelligent transportation system applications. Transportation Research Record, 78-84.
  More info

  Abstract: The development of procedures for creating bus route information is discussed as part of a Global Positioning System (GPS)-based bus inventory database in urban transit systems for intelligent transportation system applications. In the past, bus route information was usually entered into the database through geographic information system tools. Procedures involved in data entry were often very tedious. This study utilizes GPS technology to automate the process of generating data inventory for bus route information. An efficient algorithm was developed in this study for capturing the route information on the basis of a sequence of vehicle location data. ThE algorithm can be readily implemented with computer programs. The route information obtained from the algorithm is compared with the field bus trajectory data collected in Blacksburg, Virginia. In particular, comparison was made for different digitizing intervals and different bus routes. The results show that the route map created is sufficiently accurate for many applications. The route map information obtained from this study is particularly useful for the development of transit information systems to (a) predict arrival time of the next bus and (b) track schedule adherence of individual buses.
• Lin, W., Qingying, L. u., & Dahlgren, J. (2002). Dynamic procedure for short-term prediction of traffic conditions. Transportation Research Record, 149-157.
  More info

  Abstract: Many existing models for forecasting traffic conditions are based on traffic flows. Field data are used here to show that these traffic conditions may not fluctuate from day to day in the same manner as does the traffic flow. Consequently, flow data are inappropriate for predicting traffic conditions because the same flow level may correspond to either a congested or a free-flow traffic state, a phenomenon that can be easily explained with the flow-density relationship. Occupancy, which is proportional to density, is a better indicator of traffic condition. A simple dynamic model based on occupancy data is proposed. The model utilizes occupancy and occupancy increments in an integrated way and treats them as two random variables represented by two normal distribution functions. It is shown that flow data, which are more stable than occupancy data, can be used indirectly to improve the performance of the proposed model. Self- and cross-validation efforts are made to examine the performance of the model. The results are promising. The expected absolute deviance for predicted occupancy (ranging from 0 to 100%) is about 1.25 %, which is accurate enough for most applications. The model requires little effort in calibration and computation and is exceedingly simple to implement in the field.
• Lin, W. -. (2001). A Gaussian maximum likelihood formulation for short-term forecasting of traffic flow. IEEE Conference on Intelligent Transportation Systems, Proceedings, ITSC, 150-155.
  More info

  Abstract: Traffic counts are key data generated by traffic surveillance systems. In predicting traffic flows, it is commonplace to assume that traffic at a given location repeats itself from day to day and the change in traffic happens gradually rather than abruptly. Consequently, many existing models for short-term traffic flow forecasting use historical traffic information, real-time traffic counts, or both. This paper proposes a new model based on the Gaussian maximum likelihood method, which explicitly makes use of both historical information and real-time information in an integrated way. The model considers flows and flow increments jointly and treats them as two random variables represented by two normal distribution functions. Each assumption made in the model is verified against the field data. The physical structure of the model is easy to interpret. Computationally, the model is simple to implement and little effort is required for model calibration. The performance of the proposed model is compared with four other models using field data. The proposed model consistently yields predictions with the smallest absolute deviance and the smallest mean square error.
• Lin, W. -. (2001). An enhanced 0-1 mixed integer LP formulation for the traffic signal problem. IEEE Conference on Intelligent Transportation Systems, Proceedings, ITSC, 189-194.
  More info

  Abstract: An enhanced 0-1 mixed integer linear programming formulation is proposed for the traffic signal optimization problem based on the cell transmission model. The formulation has several new features that are unavailable in other existing models. The formulation handles physical queues, the number of stops, fixed or dynamic cycle length and splits, and lost time. The unintended vehicle holding problem, common in many existing analytical models, is eliminated in the proposed formulation. The formulation can be used for developing strategies for adaptive traffic control systems. Since the formulation is exact, it can also be used as a benchmark for examining the convergence behavior of existing heuristic algorithms based on the genetic algorithm, fuzzy logic, neural network or other approaches. The formulation can be solved using standard math programming optimizers. The number of 0-1 integers used in the formulation is equal to the total number of intersections multiplied by the length of the entire optimization period.
• Lin, W., & Lo, H. K. (2000). Are the objective and solutions of dynamic user-equilibrium models always consistent?. Transportation Research Part A: Policy and Practice, 34(2), 137-144.
  More info

  Abstract: Existing dynamic user-equilibrium traffic assignment (DUETA) models are mostly expanded from the static user-equilibrium traffic assignment model by introducing the time dimension along with a group of additional constraints. Whereas the equivalency between the solution to the traffic assignment model and the user-equilibrium condition as defined by Wardrop is well established in the static case, the same may not be true for the dynamic case. This paper examines the general form of DUETA models as proposed in previous research and shows that, if queuing behavior is represented in the model at a minimal level, the solution to conventional DUETA models with an objective function of the form adopted by most existing formulations may not necessarily converge to or approximate the Wardropian user-equilibrium condition in the dynamic sense as defined by many researchers.
• Lin, W., & Zeng, J. (1999). Experimental study of real-time bus arrival time prediction with GPS data. Transportation Research Record, 101-109.
  More info

  Abstract: Bus headway in a rural area usually is much larger than that in an urban area. Providing real-time bus arrival information could make the public transit system more user-friendly and thus enhance its competitiveness among various transportation modes. As part of an operational test for rural traveler information systems currently ongoing in Blacksburg, Virginia, an experimental study has been conducted on forecasting the arrival time of the next bus with automatic vehicle location techniques. The process of developing arrival time estimation algorithms is discussed, including route representation, global positioning system (GPS) data screening for identifying data quality and delay patterns, algorithm formulation, and development of measures of performance. Whereas GPS-based bus location data are adopted in all four algorithms presented, the extent to which other information is used in these algorithms varies. In addition to bus location data, information relevant to the performance of an algorithm includes scheduled arrival time, delay correlation, and waiting time at time-check stops. The performance of an algorithm using different levels of information is compared against three criteria: overall precision, robustness, and stability. Results show that at the site where the study is being conducted, the dwell time at time-check stops is most relevant to the performance of an algorithm.
• Cao, J., & Lin, W. (1998). Optimal operation for rail transit systems under advanced information. Transportation Planning and Technology, 22(2), 109-123.
  More info

  Abstract: Rail transit is normally operated on a fixed train schedule (timetable), designed based on data from typical days. In practice, however, unexpected fluctuations in passenger flow and/or in facilities may occur, making the original schedule unrealizable or non-optimal. This calls for a real-time Decision Support System (DSS) which can assist transit operators to effectively adjust the train schedule on the real-time basis when the operation environment changes markedly. Such a system can be made possible by the latest developments in intelligent transportation technologies. As the theoretical part of an operational DSS, this paper presents an optimization model, based on information available from the advanced surveillance technologies (e.g. the current situation of facilities, the short-term prediction of passenger flow, etc.), to optimize the real-time train schedule for a specific time horizon. An approximation algorithm for this model is proposed and some computational results are reported.
• Daganzo, C. F., Lin, W., & M., J. (1997). A simple physical principle for the simulation of freeways with special lanes and priority vehicles. Transportation Research Part B: Methodological, 31(2), 103-125.
  More info

  Abstract: This paper presents a simple physical principle that can be used to solve the kinematic wave problem for freeways with special lanes and priority vehicles. The principle is shown to yield the flows for all possible 'Riemann problems' arising in a homogeneous highway, so that its application in a simulation is equivalent to the Godunov 'classic' finite difference approximation method. The principle is appealing because its physical basis, unlike purely mathematical formulae, suggests a natural way in which boundary conditions for practical problems may be treated. Perhaps the IT principle will prove useful for solving general problems, e.g. involving multicommodity networks. This issue deserves more study. As an illustration of this potential the paper shows that an IT simulation of the finite highway problem solved in the companion paper (Daganzo, Transportation Research B, 31, 83-102, 1997) matches rather well the exact solution. Additional tests using other boundary conditions for the same problem also revealed a good match, © 1997 Elsevier Science Ltd. All rights reserved.
• Lin, W., & Daganzo, C. F. (1997). A simple detection scheme for delay-inducing freeway incidents. Transportation Research Part A: Policy and Practice, 31(2), 141-155.
  More info

  Abstract: This paper describes a freeway incident detection scheme that does not rely on complicated theories. The procedure compares the occupancy information recorded by two neighboring loop detectors to determine whether an incident has occurred in the intervening segment, using a recipe that is directly related to an intrinsic property of delay-inducing incidents. The method, which can also signal the termination of a detected incident, assumes that any significant bottlenecks are located outside the segment in question; i.e. that the segment is "homogeneous". Independent of complicated theories, the proposed method can be applied with little calibration to any site despite the presence of detector errors and statistical fluctuations. It is also possible to use site-independent (default) parameters, although one should then expect a somewhat inferior performance. Tests with five sets of 30 s data from three different sites in the United States, Canada, and the Netherlands, using the recommended default parameters, were encouraging. The resulting graphical displays included in this paper clearly illustrate the scheme's effectiveness in distinguishing non-recurrent from recurrent congestion. Copyright © 1997 Elsevier Science Ltd.