Macroscopic traffic models: Shifting from densities to “Celerities”

The advent of techniques to measure velocities of “GPS equipped vehicles” using satellite technology, replacing the density of the road traffic sensors, motivates and justifies the revision of conceptual, mathematical algorithms and software based models. This paper summarizes studies on the traffic evolutions achieving the minimum of a congestion function controlled “macroscopic traffic velocities” called “celerities” instead of founding traffic regulation on the measures of traffic densities. The flux valued function is the Fenchel transform of the fundamental diagram and is a convex decreasing function. We use the properties of capture basins investigated in viability theory, specifically a Lax-Hopf formula characterizing them and the “Max-Plus” morphism of capture basins for deriving the statements proved in this paper. Traffic conditions involve as well boundary conditions or conditions on trajectories inside the domain.     

On monoids over which all generators satisfy a flatness property

This paper addresses conditions under which all generators in the category of right S-acts (where S is a monoid) satisfy a flatness property. There are characterizations for monoids over which all generators satisfy a flatness property α where α can stand for freeness, projectivity, strong flatness, Condition (P), principal weak flatness and torsion freeness. To our knowledge, the problem has not been studied for other flatness properties such as weak flatness, Condition (E) and regularity. The present paper addresses this gap.     

北京市道路交通事故致死率的分析与预测

根据北京市道路交通事故的统计资料,以交通事故致死率为指标,对北京市目前道路交通安全情况进行评价.并基于灰色预测理论,建立北京市道路交通事故死亡人数的灰色GM(1,1)预测模型.预测结果显示,北京市未来几年道路交通事故死亡人数虽处于下降趋势,但死亡人数仍在千人左右,平均每起事故死亡人数仍处于上升趋势,道路交通事故致死率仍然偏高.道路交通管理部门应加大惩治道路交通违法行为力度,以控制道路交通事故的严重后果.     

Stabilization of traffic flow in optimal velocity model via delayed-feedback control

Traffic jams may occur due to various reasons, such as traffic accidents, lane reductions and on-ramps. In order to suppress the traffic congestion in an optimal velocity traffic model without any driver’s delay taken into account, a delayed-feedback control of both displacement and velocity differences is proposed in this study. By using the delay-independent stability criteria and the H_∞-norm, the delayed-feedback control can be determined to stabilize the unstable traffic flow and suppress the traffic jam. The numerical case studies are given to demonstrate and verify the new control method. Furthermore, a comparison is made between the new control method and the method proposed by Konishi et al. [K. Konishi, M. Hirai, H. Kokame, Decentralized delayed-feedback control of an optimal velocity traffic model, Eur. Phys. J. B 15 (2000) 715–722]. The results show that the new control method makes the traffic flow more stable and improves the control performance.     

A hierarchical clustering scheme approach to assessment of IP-network traffic using detrended fluctuation analysis

This paper presents an approach to the assessment of IP-network traffic in terms of the time variation of self-similarity. To get a comprehensive view in analyzing the degree of long-range dependence (LRD) of IP-network traffic, we use a hierarchical clustering scheme, which provides a way to classify high-dimensional data with a tree-like structure. Also, in the LRD-based analysis, we employ detrended fluctuation analysis (DFA), which is applicable to the analysis of long-range power-law correlations or LRD in non-stationary time-series signals. Based on sequential measurements of IP-network traffic at two locations, this paper derives corresponding values for the LRD-related parameter α that reflects the degree of LRD of measured data. In performing the hierarchical clustering scheme, we use three parameters: the α value, average throughput, and the proportion of network traffic that exceeds 80% of network bandwidth for each measured data set. We visually confirm that the traffic data can be classified in accordance with the network traffic properties, resulting in that the combined depiction of the LRD and other factors can give us an effective assessment of network conditions at different times.     

A simulation optimization-based decision support tool for mitigating traffic congestion

Traffic congestion has grown considerably in the United States over the past 20 years. In this paper, we develop a robust decision support tool based on simulation optimization to evaluate and recommend congestion mitigation strategies to transportation system decision-makers. A tabu search-based optimizer determines different network design strategies on the road network while a traffic simulator evaluates the goodness of fit. The tool is tested with real-world traffic data.     

Intersection properties in geometry

In dealing with geometries and diagrams we often need some axioms on the intersections of shadows. Here are the most usual ones: the Intersection Property (see (IP) in [3]), conditions (Int) and (Int′) of [8], and the Linearity Condition (see (GL) in [3]). An example due to Brower shows that the Linearity Condition (GL) is weaker than the Intersection Property (IP). In this paper we point out some conditions which have to be added to (GL) in order to get (IP), and we describe some of the relations between these conditions and each of the four ‘intersection’ properties given above. We summarize most of these connections in the appendix to this paper. The main open question is: ‘Which are the “right” axioms for “good” geometries?’     

基于多维模糊关联规则的道路交通阻断分析方法

交通阻断成因复杂,与气象环境、道路线形、车辆状态以及交通环境等多因素相关。由于缺乏对造成交通阻断相关因素间潜在关联的研究,交通阻断管控一直是公路管理,特别是高速公路管理的难点。本文提出了一种基于多维模糊关联规则的道路交通阻断分析方法,发掘交通阻断的潜在规律和各因素间的关联关系。首先在国家现有相关划分体系和大量交通阻断(事件)案例的基础上,根据道路管理实际需求,建立了交通阻断多维属性模型,然后利用基于FCM的模糊关联规则,挖掘阻断因素的多维属性的依存关系,得到面向道路交通阻断分析的多维模糊关联规则。通过研究成果的实践应用,证明关联规则可以为道路交通阻断预防和管理提供有效支持,在道路交通阻断分析领域有着良好的应用前景。     

Approximate dynamic programming with Bézier Curves/Surfaces for Top-percentile Traffic Routing

Multi-homing is used by Internet Service Providers (ISPs) to connect to the Internet via different network providers. This study develops a routing strategy under multi-homing in the case where network providers charge ISPs according to top-percentile pricing (i.e. based on the θth highest volume of traffic shipped). We call this problem the Top-percentile Traffic Routing Problem (TpTRP).Solution approaches based on Stochastic Dynamic Programming require discretization in state space, which introduces a large number of state variables. This is known as the curse of dimensionality in state space. To overcome this, in previous work we have suggested to use approximate dynamic programming (ADP) to construct value function approximations, which allow us to work in continuous state space. The resulting ADP model provides well performing routing policies for medium sized instances of the TpTRP. In this work we extend the ADP model, by using Bézier Curves/Surfaces to obtain continuous-time approximations of the time-dependent ADP parameters. This modification reduces the number of regression parameters to estimate, and thus accelerates the efficiency of parameter training in the solution of the ADP model, which makes realistically sized TpTRP instances tractable. We argue that our routing strategy is near optimal by giving bounds.     

Fast heuristics for protection networks for dynamic routing

Traffic volatility and network reliability are important issues in the provision of high speed network services. We consider the construction of a second network, the protection network which can carry overload traffic due to the failure or congestion of any two links in the original network. The level of protection against such contingencies can be specified by a traffic requirement matrix. We construct a fully connected protection network, for an n node network, using an O(n²) heuristic based on the largest two traffic requirements for each node. This procedure is then modified to generate a more effective O(n⁴) heuristic, both methods facilitate fast processing for two-hop dynamic routing. We compare the performance of the heuristics with the O(n¹⁵) optimal solution.     

Vector-valued invariant means revisited

We show that a Banach space X is complemented in its ultraproducts if and only if for every amenable semigroup S the space of bounded X-valued functions defined on S admits (a) an invariant average; or (b) what we shall call “an admissible assignment”. Condition (b) still provides an equivalence for quasi-Banach spaces, while condition (a) necessarily implies that the space is locally convex.     

Buffer overflow calculations using an infinite-capacity model

Sufficient conditions are established for approximation of the overflow probability in a stochastic service system with capacity C by the probability that the related infinite-capacity system has C customers. These conditions are that (a) the infinite-capacity system has negligible probability of C or more customers; (b) the probabilities of states with exactly C customers for the infinite-capacity system are nearly proportional to the same probabilities for the finite- capacity system. Condition (b) is controlling if the probabilities for the infinite-capacity system are rescaled so that the probability of at most C customers is unity. For systems with precisely one state with C customers, such as birth-and-death processes, the latter approximation is exact even when condition (a) does not hold.     

A hybrid macroscopic-based model for traffic flow in road networks

Recently, the unquestionable growth of interest to increase the operational efficiency and capability of transportation systems led to the development of a large number of traffic modeling theories. One of the major operational issues when developing a transportation system management model lies in the selection of the appropriate methodological approach with respect to several decisions, such as the selection of the type of input and output data as well as the qualitative representation and the computational power of the model. Despite the considerable effort in the area, there is still not an approach which per se models effectively the various dynamically evolving features of traffic in road networks. The present paper addresses this issue by introducing a new hybrid approach which combines the complementary features and capabilities of both continuum mathematical models e.g. 1, 6, 23 and 26 and knowledge-based models e.g. 7, 22 and 28 in order to describe effectively traffic flow in road networks.     

Analysis and control of maritime transit traffic through the İstanbul Channel: a simulation approach

This study involves a functional simulation model for the maritime transit traffic in the İstanbul Channel that investigates the Channel Traffic Rules and Regulations, vessel types, cargo characteristics, meteorological and geographical conditions, pilotage and tugboat services. The simulation model mainly focuses on the transit traffic in the Channel. This study provides a platform to analyze the effects of factors such as Rules and Regulations, number of tugboats and pilots, vessel type, traffic density and meteorological conditions on the maritime traffic in the Channels. Results obtained and reported in the study clearly indicate some interesting relationships among these factors. As the effect of five factors on eight responses are examined, the most significant factor is determined as number of pilots and tugboats in the service, while the second effective factor is the arrival rate of vessels.     

The L q spectra and Rényi dimension of generalized inhomogeneous self-similar measures

Very recently bounds for the L ^q spectra of inhomogeneous self-similar measures satisfying the Inhomogeneous Open Set Condition (IOSC), being the appropriate version of the standard Open Set Condition (OSC), were obtained. However, if the IOSC is not satisfied, then almost nothing is known for such measures. In the paper we study the L ^q spectra and Rényi dimension of generalized inhomogeneous self-similar measures, for which we allow an infinite number of contracting similarities and probabilities depending on positions. As an application of the results, we provide a systematic approach to obtaining non-trivial bounds for the L ^q spectra and Rényi dimension of inhomogeneous self-similar measures not satisfying the IOSC and of homogeneous ones not satisfying the OSC. We also provide some non-trivial bounds without any separation conditions.     

The interval function of a connected graph and road systems

Let V be a finite nonempty set. In this paper, a road system on V (as a generalization of the set of all geodesics in a connected graph G with V(G)=V) and an intervaloid function on V (as a generalization of the interval function (in the sense of Mulder) of a connected graph G with V(G)=V) are introduced. A natural bijection of the set of all intervaloid functions on V onto the set of all road systems on V is constructed. This bijection enables to deduce an axiomatic characterization of the interval function of a connected graph G from a characterization of the set of all geodesics in G.     

Field test of nonintrusive traffic detection technologies

Accurate, low-cost methods of collecting historical traffic information are essential in making well-informed transportation planning decisions. In addition, detection of real-time traffic conditions is a key element in advanced traffic management and traveler information systems.Until the last decade, inductive loop detectors, pneumatic road tubes, and temporary manual counts were the primary methods for collecting both real-time and historical traffic data. However, technological innovations have given rise to design many different types of advanced traffic detectors. Recently developed traffic detectors use sonic, ultrasonic, microwave, or infrared energy. Most of these detectors can be mounted overhead or to the side of traffic lanes. Magnetic sensors are now being built in sizes small enough to be placed in conduits under the roadway. Artificial intelligence algorithms can process videotaped images of road scenes and output many useful traffic parameters.Even though nonintrusive technologies have been available for several years, there are still many uncertainties regarding their use. Traffic engineers lack a comprehensive comparison of the various types of traffic detection technology. A study conducted by the Minnesota Department of Transportation(Mn/DOT) and SRF Consulting Group, Inc. (SRF) and sponsored by the Federal Highway Administration (FHWA) seeks to address this need. Mn/DOT and SRF undertook a two-year effort to test a wide variety of nonintrusive traffic detection technologies. The purpose of this evaluation was to collect practical information on the performance, installation requirements, long-term maintenance requirements, and costs of various types of nonintrusive traffic detection technologies. More than a dozen devices representing magnetic, sonic, ultrasonic, microwave, infrared, and video image processing technologies were evaluated during this project. Devices were evaluated for their performance in both freeway and urban intersection monitoring situations.Testing consisted of two phases. During Phase I, which ran from November 1995 to January 1996, all participating devices measured traffic data on three lanes of Interstate 394 in Minneapolis at the Penn Avenue interchange. Phase II, which ran from February to November 1996, consisted of an all-season monitoring of the devices' performance and maintenance requirements and involved both freeway and intersection installations. The Minneapolis-St. Paul metropolitan area provided an excellent opportunity to evaluate the devices in many types of weather extremes, including very cold and very hot temperatures, rain, snow, fog, and high winds.     

Short-term forecasting of traffic delays in highway construction zones using on-line approximators

Highway construction zones are often the cause of traffic delays. This is a natural consequence of the high congestion and nonuniform traffic flow conditions in construction zones. Most of the current algorithms for computing traffic delays are accurate for low density traffic conditions, and address the estimation of current travel time only. This paper presents a method for short-term forecasting of traffic delays in highway construction zones using data from presence detectors. The method is based on a modular approach wherein data from adjacent detectors is processed for estimating the travel time between the two detectors. The travel time estimates are then considered as time-series data, and the problem of short-term forecasting of traffic delay is formulated as a time-series evolution problem. A generic structure referred to as an on-line approximator is used for the prediction of travel time based on current and past travel time estimates. Simulation examples are used to illustrate the traffic delay forecasting algorithm.     

Analysis of a queueing system with a general service scheduling function,with applications to telecommunication network traffic control

In this paper we analyze a queueing system with a general service scheduling function. There are two types of customer with different service requirements. The service order for customers of each type is determined by the service scheduling function α_k(i, j) where α_k(i, j) is the probability for type-k customer to be selected when there are i type-1 and j type-2 customers. This model is motivated by traffic control to support traffic streams with different traffic characteristics in telecommunication networks (in particular, ATM networks). By using the embedded Markov chain and supplementary variable methods, we obtain the queue-length distribution as well as the loss probability and the mean waiting time for each type of customer. We also apply our model to traffic control to support diverse traffics in telecommunication networks. Finally, the performance measures of the existing diverse scheduling policies are compared. We expect to help the system designers select appropriate scheduling policy for their systems.