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Browsing by Author "Zou, Xi"

Now showing 1 - 9 of 9
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    Benefit-Cost Analysis for Intersection Decision Support
    (Minnesota Department of Transportation, 2007-10) Corbett, Michael; Levinson, David; Zou, Xi
    The Intersection Decision Support (IDS) system is designed to assist drivers on stop-controlled low-volume rural roads choosing gaps when confronted with busy multiple lane divided-highways, without affecting traffic on the high-volume road. The hope is, that by providing better gap guidance, fewer crashes (and fatalities) will occur. This research develops a framework for analyzing such a new, and presently under-specified technology, and illustrates that framework by comparing that with more conventional engineering approaches, as well as a "do-nothing" base case. The results show that the IDS System may be an effective tool to reduce crash rates at various intersections. More research is needed to address reliability and stability issues, and in determining how cost- effective of a solution the IDS System is compared to other "traditional" alternatives.
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    Detecting the Breakdown of Traffic
    (2006) Zou, Xi; Levinson, David M
    Timely traffic prediction is important in advanced traffic management systems to make possible rapid and effective response by traffic control facilities. From the observations of traffic flow, the time series present repetitive or regular behavior over time that distinguishes time series analysis of traffic flow from classical statistics, which assumes independence over time. By taking advantage of tools in frequency domain analysis, this paper proposes a new criterion function that can detect the onset of congestion. It is found that the changing rate of the cross-correlation between density dynamics and flow rate determines traffic transferring from free flow phase to the congestion phase. A definition of traffic stability is proposed based on the criterion function. The new method suggests that an unreturnable transition will occur only if the changing rate of the cross-correlation exceeds a threshold. Based on real traffic data, detection of congestion is conducted in which the new scheme performs well compared to previous studies.
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    Evaluation of Impacts of Adaptive Cruise Control on Mixed Traffic Flow
    (American Society of Civil Engineers, 2002) Zou, Xi; Levinson, David M
    Evaluation of Impacts of Adaptive Cruise Control on Mixed Traffic Flow Abstract: This paper addresses the impacts of Adaptive (Intelligent) Cruise Control (ACC) laws on traffic flow. Semi-automated vehicles, such as ACC Vehicles, with the capability to automatically follow each other in the same lane, will coexist with manually driven vehicles on the existing roadway system before they become universal. This mixed fleet scenario creates new capacity and safety issues. In this paper, simulation results of various mixed fleet scenarios under different ACC laws are presented. Explicit comparison of two ACC laws, Constant Time Headway (CTH) and Variable Time Headway (VTH), are based on these results. It¹s found that the latter one has better performance in terms of capacity and stability of traffic. Throughput increases with the proportion of CTH vehicles when flow is below capacity conditions. But above capacity, speed variability increases and speed drops with the CTH traffic compared with manual traffic, while the VTH traffic always performs better.
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    Financing and Deploying Automated Freight Systems
    (Edward Elgar Publishers, 2006) Levinson, David M; Zou, Xi
    New technologies are bringing Automated Freight Systems (AFS), which aim to reduce congestion, mitigate environmental impacts and enhance public safety, to fruition. The financing and deployment issues of AFS differ from other Intelligent Transport System applications. This chapter briefly introduces major concepts of AFS. The financing strategies for these concepts are discussed, in which the government subsidies play an important role through the use of public-private partnership. Economies of scale and externalities of the current and new systems are discussed. In the discussion of the deployment of AFS, it is suggested that deployment schemes are highly correlated with financing strategies.
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    A Framework for Analyzing the Effects of Spring Load Restriction
    (2004) Levinson, David M; Li, Ning; Zou, Xi; Smalkoski, Brian
    Spring Load Restrictions (SLR) impose load restrictions on heavy trucks during the spring thaw period. Although the policies have been implemented for many years, we are still unsure of their economic effects on truckers. This paper overviews practices around the world and sets up a framework to estimate the Benefit/Cost of the SLR policy. A freight demand model in Minnesota was built to estimate the impacts of SLR on the freight transportation pattern. The model allows various policy scenarios to be tested before being tested in practice. A preliminary result of the freight demand model shows the SLR policy increased truck Vehicle Kilometers of Travel (VKT) in Lyon County, Minnesota by about 13 percent.
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    Modeling Pipeline Driving Behaviors: A Hidden Markov Model Approach
    (Transportation Research Board, 2006) Zou, Xi; Levinson, David M
    Driving behaviors at intersection are complex because drivers have to perceive more traffic events than normal road driving and thus are exposed to more errors with safety consequences. Drivers make real-time responsesin a stochastic manner. This paper presents our study using Hidden Markov Models (HMM) to model driving behaviors at intersections. Observed vehicle movement data are used to build up the model. A single HMM is used to cluster the vehicle movements when they are close to intersection. The re-estimated clustered HMMs provide better prediction of the vehicle movements compared to traditional car-following models. Only through vehicles on major roads are considered in this paper.
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    A Multi-Agent Congestion and Pricing Model
    (Hong Kong Society for Transportation Studies, 2006) Zou, Xi; Levinson, David M
    A multi-agent model of travelers competing to utilize a roadway in time and space is presented in this paper to illustrate the effect of congestion and pricing on traveler behaviors and network equilibrium. To realize the spillover effect among travelers, N-player games are constructed in which the strategy set include (N+1) strategies. We solve the discrete N-player game (for N less than 8) and find Nash equilibria if they exist. This model is compared to the bottleneck model. The results of numerical simulation show that the two models yield identical results in terms of lowest total costs and marginal costs when a social optimum exists.
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    Sharing Data Between Arc/Info and Emme/2: Practice in Lyon County, Minnesota
    (2004) Li, Ning; Zou, Xi; Levinson, David M
    Sharing data between GIS software (Arc/Info) and Traffic Demand Modeling Software (EMME/2) has long been an issue of interest to traffic engineers. A literature review and evaluation of current efforts on the data exchange is given in this paper. The authors also developed their own economical method to realize the data transform through Matlab programming. As a practice, a model of the truck flow pattern in Lyon County, Minnesota is developed by the integrated use of Arc/Info, EMME/2, Enif, and the Matlab program. The combined use of these programs overcame the disadvantage of a single software and achieved expected objective. The program is free to anyone who have interests.
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    Vehicle Based Intersection Management with Intelligent Agents
    (ITS America, 2003) Zou, Xi; Levinson, David M
    Signal-based intersection management will change when vehicles with intelligent capability are available in the future. Intelligent agents embedded in vehicle software will be responsible for vehicle control and route guidance. Intersection management can be achieved through the collaboration of these agents, without a centralized control infrastructure. This research focuses on the use of distributed multi-agent systems to provide microscopic adaptive control which might reduce traffic delay and chances of collisions at intersections. A hypothesized Mobile Ad-hoc Network provides communication links to connect the agents.