Queue Build-up Research Articles

Performance Evaluation of a Multi-Standard Fast Charging Station for Electric Vehicles

Electric vehicles (EVs) have been considered as a feasible solution to deal with the high fuel consumption and greenhouse gas emissions caused by conventional vehicles. However, long charging times and drivers’ range anxiety are the main disadvantages of EVs. A key factor that is expected to mitigate these problems and facilitate the wide adoption of EVs will be the effective operation of fast charging stations (FCSs). In this paper, the operation of a FCS is evaluated, in terms of operator’s profits and customers’ waiting time in the queue. The FCS contains both dc and ac outlets that provide high power levels, while the various EV models are classified by their battery size and the fast charging option they use (dc or ac). The operator’s daily profits and the queue waiting time are initially computed by considering that the EVs recharge under a flat-rate pricing policy. In order to avoid a long queue build-up at the FCS, a new pricing policy is then proposed. The intuition behind the scheduled pricing policy is that users are deterred to charge more than an arranged energy threshold, thus reducing the load and the waiting time at the FCS.

The Use of Queuing Theory in the Management of Traffic Intensity

One of the major objectives of road transport policy is to minimize road congestion and road accidents in an area. An intense interruption of free movement on a road is known as traffic congestion. Traffic congestion is as a result of too many cars, buses, trucks in a road space at a particular time. It can occur almost on any road system. It is more dominant and severe around central business district, industrial areas and the like, during the morning and afternoon periods as a result of the influx of commuters and goods delivery around such areas. The impact of such traffic congestion includes delay in delivery of goods and services, excessive fuel consumption and pollution, frustration and inability to estimate travel time. Road transport which is popularly used as medium for mobility can be tiring, irritating and costly when congestion is encountered. This work contributes to the prediction of road traffic intensity of some areas in Lagos state, Nigeria by the application of queuing theory. The approach adopted in the paper describes traffic intensity as performance measure used in the prediction of the level of queue build-up at traffic light intersection in the selected area. The prediction may enhance proper traffic management devoid of undue delays.

The Effectiveness of Random Early Detection in Data Center Transmission Control Protocol-Based Cloud Computing Networks

Wireless cloud computing environment becomes an important element of Internet. The underlying transport layer protocol in such environment should efficiently deal with high bursty traffic tolerance, presents low delays, and offers high throughput. DCTCP is the common cloud transport protocol that is capable of tackling TCP incast and queue build-up problems. However, its performance is considerably degraded when there are tens of servers responding to one aggregator simultaneously. In this paper, the performance of DCTCP with the utilization of RED queue management mechanism is evaluated. The evaluation results showed that there is a tradeoff in the use of RED. On one hand, RED is not good for short-lived and medium-lived connections as it presents higher completion time delay compared to the normal DCTCP mechanism. On the other hand, it presentsacceptable delay for longlived connections but at the cost of throughput.

Refinement of Performance Measures based on High-Resolution Signal and Detection Data

Abstract: Most previous evaluation studies of various signal control strategies, both in the field and through microsimulation, used common traffic performance measures (PMs) related to travel times, number of stops, control delay, etc.. Recent advancements in detection and controller data-logging capabilities have brought forth new types of signal PMs. Two such measures known as Arrivals on Green (AOG) and Approach Delay (AD) have been recently used in a number of projects by other universities and state departments of transportation. A study that evaluated InSync through these high-resolution PMs showed that AOG, as a single PM, cannot be fully trusted when comparing traffic signal alternatives, as it does not reflect the efficiency of the allocated green time used by an arriving platoon of vehicles. The findings also suggested that currently used methodologies underestimate AD, as they simplify their computation. This study proposes development of a new high-resolution PM – Average Arrivals on Green Ratio (AAOGR) that takes into account variability of cycle length and green time, on a cycle-by-cycle basis (thus applicable for dynamic control) and provides information on the ratio of vehicles that passed through the intersection per a second of green time. Moreover, a discharge rate-based model for computing AD, which takes into consideration the possible queue build-up during red and provides better estimation of true AD per vehicle if measured in front of the advanced detectors, is proposed as well.

Exploring the impact of a coordinated variable speed limit control on congestion distribution in freeway

Over the past few decades, urban freeway congestion has been highly recognized as a serious and worsening traffic problem in the world. To relieve freeway congestion, several active traffic and demand management (ATDM) methods have been developed. Among them, variable speed limit (VSL) aims at regulating freeway mainline flow upstream to meet existing capacity and to harmonize vehicle speed. However, congestion may still be inevitable even with VSL implemented due to extremely high demand in actual practice. This study modified an existing VSL strategy by adding a new local constraint to suggest an achievable speed limit during the control period. As a queue is a product of the congestion phenomenon in freeway, the incentives of a queue build-up in the applied coordinated VSL control situation were analyzed. Considering a congestion occurrence (a queue build-up) characterized by a sudden and sharp speed drop, speed contours were utilized to demonstrate the congestion distribution over a whole freeway network in various scenarios. Finally, congestion distributions found in both VSL control and non-VS control situations for various scenarios were investigated to explore the impact of the applied coordinated VSL control on the congestion distribution. An authentic stretch of Whitemud Drive (WMD), an urban freeway corridor in Edmonton, Alberta, Canada, was employed to implement this modified coordinated VSL control strategy; and a calibrated micro-simulation VISSIM model (model functions) was applied as the substitute of the real-world traffic system to test the above mentioned performance. The exploration task in this study can lay the groundwork for future research on how to improve the presented VSL control strategy for achieving the congestion mitigation effect on freeway.

Rough cut capacity planning-(RCCP)-(case study)

Many people are familiar with the Manufacturing Planning and Control (MPC) Systems which are driven by Material requirements planning (MRP) engines. In such systems MRP uses a master production schedule (MPS) of end items to determine the quantity and timing of component parts’ production. MRP does not consider any capacity limitation; it strictly assumes that, sufficient capacity is available to produce components at the time when they are needed. The most common problem which is encountered in operating MRP based systems is the existence of an overstated MPS. An overstated master production schedule is the one which orders more than the production resources can complete. An overstated MPS causes raw materials and WIP inventories to increase because more materials are purchased and released to the shop than are completed and shipped. It also causes a buildup of queues on the shop floor. Since jobs have to wait to be processed, actual lead times increase, causing ship dates to be missed. As lead times increase, forecast over the planning horizon becomes less accurate. This is because of the fact that, forecasts are more accurate for shorter periods than for longer ones. Thus, overstated master production schedules lead to missed due dates. Because of all the above given reasons, validating the MPS with respect to available capacity is an extremely important step in MRP. The term used for this validation exercise is “Rough Cut Capacity Planning (RCCP)”. The methods commonly used in energy planning outline is a technique factors College ((Overall Factors, and is a way to convert the amount of products contained in the scheduling main production to the power requirements are expressed in hours of work a total of some or all production resources (processes or certain sections). Then these requirements are being distributed from the total energy required to types of energy depending on the rates of use of each type to

The efficacy of centralized flow rate control in 802.11-based wireless mesh networks

Commodity WiFi-based wireless mesh networks (WMNs) can be used to provide last mile Internet access. These networks exhibit extreme unfairness with backlogged traffic sources. Current solutions propose distributed source-rate control algorithms requiring link-layer or transport-layer changes on all mesh nodes. This is often infeasible in large practical deployments. In wireline networks, router-assisted rate control techniques have been proposed for use alongside end-to-end mechanisms. We wish to evaluate the feasibility of establishing similar centralized control via gateways in WMNs. In this paper, we focus on the efficacy of this control rather than the specifics of the controller design mechanism. We answer the question: Given sources that react predictably to congestion notification, can we enforce a desired rate allocation through a single centralized controller? The answer is not obvious because flows experience varying contention levels, and transmissions are scheduled by a node using imperfect local knowledge. We find that common router-assisted flow control schemes used in wired networks fail in WMNs because they assume that (1) links are independent, and (2) router queue buildups are sufficient for detecting congestion. We show that non-work-conserving, rate-based centralized scheduling can effectively enforce rate allocation. It can achieve results comparable to source rate limiting, without requiring any modifications to mesh routers or client devices.

Performance evaluation of mixed-bias scheduling schemes for wireless mesh networks

Typically, peripheral nodes in a multi-hop wireless network experience poor performance from starvation, congestion, queue build-up and contention along the path towards internet gateways. We propose three adaptive methods for scheduling based on mixed-bias scheduling which aim to prioritise mesh routers near the gateways to ensure they can handle their own traffic and peripheral traffic. We also give an overview of the mixed-bias approach for scheduling. We then evaluate the performance of each technique in comparison with each other and the IEEE 802.11 distributed coordination function. Each solution is evaluated based on average packet delivery ratio and average end-to-end delay. Two experiments were performed to examine the performance. First, we studied the effect of varying the inter-arrival rate of the packets. Second we examined the effect of changing the number of sources. In all experiments, the proposed approaches perform at least as well or better than IEEE 802.11 DCF.

Estimation of Delay Induced by Downstream Operations at Signalized Intersections over Extended Control Time

Analytical macroscopic models are presented to quantify delay at signalized intersections for extended control periods (multiple cycles) attributable to downstream time-variable congestion. Each of the models consists of an upstream demand estimation algorithm, a downstream queue build-up prediction algorithm, a shockwave propagation and dissipation tracking algorithm, and an algorithm that carries traffic aftereffect of a cycle’s control into the following cycle. Model inputs are basic traffic flow properties, signal control parameters, and link geometry. The models are modular and can be incorporated into any size system for one or multiple cycles. The models were tested on a hypothetical system of closely spaced intersections and under different traffic flow, control, and geometric conditions. Results show that delay induced by downstream traffic operations on an upstream intersection can be significant and that it may change with time and reach steadiness once traffic flow, downstream queues, and signal control measures stabilize and start replicating over time. Green ratios of neighboring intersections exert a significant influence on delay. For certain green ratios and geometric combinations, offsets can exert appreciable influence as well. The delay values and their temporal variation compared well with those from a microscopic simulation model.

A shockwave profile model for traffic flow on congested urban arterials

In this paper a new traffic flow model for congested arterial networks, named shockwave profile model (SPM), is presented. Taking advantage of the fact that traffic states within a congested link can be simplified as free-flow, saturated, and jammed conditions, SPM simulates traffic dynamics by analytically deriving the trajectories of four major shockwaves: queuing, discharge, departure, and compression waves. Unlike conventional macroscopic models, in which space is often discretized into small cells for numerical solutions, SPM treats each homogeneous road segment with constant capacity as a section; and the queuing dynamics within each section are described by tracing the shockwave fronts. SPM is particularly suitable for simulating traffic flow on congested signalized arterials especially with queue spillover problems, where the steady-state periodic pattern of queue build-up and dissipation process may break down. Depending on when and where spillover occurs along a signalized arterial, a large number of queuing patterns may be possible. Therefore it becomes difficult to apply the conventional approach directly to track shockwave fronts. To overcome this difficulty, a novel approach is proposed as part of the SPM, in which queue spillover is treated as either extending a red phase or creating new smaller cycles, so that the analytical solutions for tracing the shockwave fronts can be easily applied. Since only the essential features of arterial traffic flow, i.e., queue build-up and dissipation, are considered, SPM significantly reduces the computational load and improves the numerical efficiency. We further validated SPM using real-world traffic signal data collected from a major arterial in the Twin Cities. The results clearly demonstrate the effectiveness and accuracy of the model. We expect that in the future this model can be applied in a number of real-time applications such as arterial performance prediction and signal optimization.

Dynamic network loading: A stochastic differentiable model that derives link state distributions

We present a dynamic network loading model that yields queue length distributions, accounts for spillbacks, and maintains a differentiable mapping from the dynamic demand on the dynamic queue lengths. The model also captures the spatial correlation of all queues adjacent to a node, and derives their joint distribution. The approach builds upon an existing stationary queueing network model that is based on finite capacity queueing theory. The original model is specified in terms of a set of differentiable equations, which in the new model are carried over to a set of equally smooth difference equations. The physical correctness of the new model is experimentally confirmed in several congestion regimes. A comparison with results predicted by the kinematic wave model (KWM) shows that the new model correctly represents the dynamic build-up, spillback and dissipation of queues. It goes beyond the KWM in that it captures queue lengths and spillbacks probabilistically, which allows for a richer analysis than the deterministic predictions of the KWM. The new model also generates a plausible fundamental diagram, which demonstrates that it captures well the stationary flow/density relationships in both congested and uncongested conditions.

Dynamic network loading: a stochastic differentiable model that derives link state distributions

We present a dynamic network loading model that yields queue length distributions, accounts for spillbacks, and maintains a differentiable mapping from the dynamic demand on the dynamic queue lengths. The model also captures the spatial correlation of all queues adjacent to a node, and derives their joint distribution. The approach builds upon an existing stationary queueing network model that is based on finite capacity queueing theory. The original model is specified in terms of a set of differentiable equations, which in the new model are carried over to a set of equally smooth difference equations. The physical correctness of the new model is experimentally confirmed in several congestion regimes. A comparison with results predicted by the kinematic wave model (KWM) shows that the new model correctly represents the dynamic build-up, spillback, and dissipation of queues. It goes beyond the KWM in that it captures queue lengths and spillbacks probabilistically, which allows for a richer analysis than the deterministic predictions of the KWM. The new model also generates a plausible fundamental diagram, which demonstrates that it captures well the stationary flow/density relationships in both congested and uncongested conditions.

An empirical analysis on the arterial fundamental diagram

For uninterrupted traffic flow, it is well-known that the fundamental diagram (FD) describes the relationship between traffic flow and density under steady state. For interrupted traffic flow on a signalized road, it has been recognized that the arterial fundamental diagram (AFD) is significantly affected by signal operations. But little research up to date has discussed in detail how signal operations impact the AFD. In this paper, based upon empirical observations from high-resolution event-based traffic signal data collected from a major arterial in the Twin Cities area, we study the impacts of g/ C ratio, signal coordination, and turning movements on the cycle-based AFD, which describes the relationship between traffic flow and occupancy in a signal cycle. By microscopically investigating individual vehicle trajectories from event-based data, we demonstrate that not only g/ C ratio constrains the capacity of a signalized approach, poor signal coordination and turning movements from upstream intersections also have significant impact on the capacity. We show that an arterial link may not be congested even with high occupancy values. Such high values could result from queue build-up during red light that occupies the detector, i.e. the Queue-Over-Detector (QOD) phenomenon discussed in this paper. More importantly, by removing the impact of QOD, a stable form of AFD is revealed, and one can use that to identify three different regimes including under-saturation, saturation, and over-saturation with queue spillovers. We believe the stable form of AFD is of great importance for traffic signal control because of its ability to identify traffic states on a signal link.

Stability of FIFO networks under adversarial models: State of the art

Network stability is an important issue that has attracted the attention of many researchers in recent years. Such interest comes from the need to ensure that, as the system runs for an arbitrarily length of time, no server will suffer an unbounded queue buildup. Over the last few years, much research has been carried out to gain an understanding of the factors that affect the stability of packet-switched networks. In this paper, we attempt to review the most noteworthy results in this area. We will focus on networks where the scheduling policy is of the FIFO type, which is, by far, the most widely adopted policy. We gather these results and present them in an organized manner. Furthermore, we also identify some directions open to future research.

Bandwidth-sharing networks in overload

Bandwidth-sharing networks as considered by Massoulié and Roberts provide a natural modeling framework for describing the dynamic flow-level interaction among elastic data transfers. Under mild assumptions, it has been established that a wide family of so-called α -fair bandwidth-sharing strategies achieve stability in such networks provided that no individual link is overloaded. In the present paper we focus on α -fair bandwidth-sharing networks where the load on one or several of the links exceeds the capacity. Evidently, a well-engineered network should not experience overload, or even approach overload, in normal operating conditions. Yet, even in an adequately provisioned system with a low nominal load, the actual traffic volume may significantly fluctuate over time and exhibit temporary surges. Furthermore, gaining insight into the overload behavior is crucial in analyzing the performance in terms of long delays or low throughputs as caused by large queue build-ups. The way in which such rare events tend to occur, commonly involves a scenario where the system temporarily behaves as if it experiences overload. In order to characterize the overload behavior, we examine the fluid limit, which emerges from a suitably scaled version of the number of flows of the various classes. The convergence of the scaled number of flows to the fluid limit is empirically validated through simulation experiments. Focusing on linear solutions to the fluid-limit equation, we derive a fixed-point equation for the corresponding asymptotic growth rates. It is proved that a fixed-point solution is also a solution to a related strictly concave optimization problem, and hence exists and is unique. We use the fixed-point equation to investigate the impact of the traffic intensities and the variability of the flow sizes on the asymptotic growth rates. The results are illustrated for linear topologies and star networks as two important special cases. Finally, we briefly discuss extensions to models with user impatience.

Practical modelling of trip re-scheduling under congested conditions

There is plenty of evidence that drivers may make small changes in their time of travel to take advantage of lower levels of congestion. However, progress in the practical modelling of such “micro” re-scheduling within peak period traffic remains slow. While there exist research papers describing theoretical solutions, techniques for practical use are not generally available. Most commonly used assignment programs are temporally aggregate, while packages which do allow some “dynamic assignment” typically assume a fixed demand profile. The aim of the paper is to present a more heuristic method which could at least be used on an interim basis. The assumption is that the demand profile can be segmented into a number of mutually exclusive “windows” in relation to the “preferred arrival time”, while on the assignment side, independently defined sequential “timeslices” are used in order to respect some of the dynamic processes relating to the build-up of queues. The demand process, whereby some drivers shift away from their preferred window, leads to an iterative procedure with the aim of achieving reasonable convergence. Using the well-known scheduling theory developed by Vickrey, Small, and Arnott, de Palma & Lindsey, the basic approach can be described, extending from the simple “bottleneck”, to which the theory was originally applied, to a general network. So far, insufficient research funds have been made available to test the approach properly. It is hoped that by bringing the ideas into the public domain, further research into this area may be stimulated.

XCP for shared-access multi-rate media

The eXplicit Control Protocol (XCP) was developed to overcome some of the limitations of TCP, such as low utilization in high bandwidth delay product networks, unstable throughput, large queue build-up, and limited fairness. XCP, however, requires that each queue controller in a path knows the exact capacity of its link. In shared access media, e.g. IEEE 802.11, knowing the actual capacity of the channel is a difficult task.In this paper we propose modifications to the XCP algorithm that enable the utilization of XCP even when the capacity of a link is unknown. These modifications are validated through simulation.We also present the results of a comparison between the performance of the modified XCP and TCP, where XCP controlled flows result more stable, fairness increases, and the network delay becomes lower. In addition, as the bandwidth delay product increases, XCP is able to maintain near-maximum utilization while TCP decreases utilization.

Dynamic vehicular delay comparison between a police-controlled roundabout and a traffic signal

Effects of queues on motorists during rush hours are severe at intersections controlled by roundabouts. Traffic police are frequently used in order to optimize the traffic flow and to control queue length at such intersections. However, the question as to how efficient such system is, compared with traffic signal, is not clear from the dynamic delay point of view. In this study a criterion is being developed based on vehicular delays as the motorist join the queues and cross the stop-line. The adopted method avoids oversimplification of reality and prevents unrealistic assumptions. The data required for the study were mainly collected through video filming technique. The results, for a given set of geometric and traffic characteristics, indicate that both a police-controlled roundabout and a traffic signal act in a similar manner in terms of vehicular delay at a certain critical value. This critical value is considered to be the point of intersection between the curves representing traffic signal and roundabout on a delay–space diagram for the vehicles as they join the tail end of the queue until they cross the stop-line. Beyond the critical value, the effect of delays and buildup of queues at roundabouts will be excessive, compared to traffic signals. Before the critical value the delays at traffic signals are quite high compared to roundabouts. The study will assist the concerned authorities to operate the existing conditions, particularly the roundabouts, more efficiently. It will also be beneficial for the traffic planners and policy makers in making judicious decisions regarding control type at intersections.

Simulating the Newspaper Preprint Insertion Process for Productivity Improvement

Abstract This article discusses how simulation can be successfully implemented to improve the productivity of newspaper preprint insertion processes. Specifically, the author demonstrates that production time loss induced by excessive queue build-up in a particular insertion process could be drastically reduced if a close-coupled machine layout was adopted in place of a remote-coupled configuration. In the remote-coupled layout, a packaging line is connected to a palletizer via a tray system under the supervision of a control room. In the close-coupled configuration, packaging line and palletizer are directly connected by a simple belt conveyor. The simulation model presented in this application suggests that the close-coupled layout could reduce production time loss induced by excessive queue build up by 95%, depending on the operating conditions.

WINTRAC: a TCP window adjustment scheme for bandwidth management

In TCP, congestion control as well as error recovery are implemented by a sliding window. The dynamics of TCP specifically, a mismatch between the TCP window and the bandwidth-delay product of the network can sometimes cause the network switches or routers to accumulate large queues, resulting in buffer overflows, reduced throughput, unfairness and underutilization. It is generally accepted that there is a limit to how much control can be accomplished from the congestion control mechanisms in the end systems. Some mechanisms are needed in the intermediate network elements to complement the endpoint congestion avoidance mechanisms. We describe in this paper, a new TCP rate control scheme based on a simple recursive algorithm. The idea behind the algorithm is to match the offered network load to the available resources by modifying at an intermediate network element, the receiver’s advertised window in TCP acknowledgments returning to the source. We show through simulations that the scheme can efficiently control TCP traffic to limit queue buildups and buffer requirements at the network nodes, resulting in significant improvements in delay, packet loss rates, fairness in the distribution of the maximum achievable window size, and link utilization.