Extended bottlenecks, the fundamental relationship, and capacity drop on freeways

This paper presents evidence that the commonly used point bottleneck model is too simplistic for freeway bottlenecks, the actual mechanism appears to occur over an extended distance. We find evidence of subtle flow limiting and speed reducing phenomena more than a mile downstream of a lane drop bottleneck. These phenomena impact the fundamental relationship, FD. Close to the lane drop the free flow regime appears to come from a “parabolic” FD, but further downstream the relationship straightens to a “triangular” FD and throughput increases. We develop a theory to explain the underlying mechanisms. These insights should help resolve the decades long debate about the shape of the FD. The phenomena also provide a mechanism that may contribute to the empirically observed capacity drop often seen at bottlenecks. Although we study a lane drop, this work should be transferable to other bottlenecks where the capacity restriction persists for an extended distance, e.g., a corridor with a fixed number of lanes and an on-ramp bottleneck.     

Understanding the ocean container market—a seven country study [1]

Carrier selection criteria have been an issue in carrier marketing since the 1970s. Investigator location and interest has usually limited customer surveys to one geographic market. Market characteristics—differing purchase and service characteristics—have led to model seperation in the studies undertaken and sample size has constrained most researchers to reporting results as though customers were homogeneous in their needs. This has resulted in price versus service debates with conflicting conclusions. This paper explores the differences in the importance of various ocean container carrier selection criteria on the North Atlantic route for discrete geographic and customer segments. The paper reviewss the carrier selection literature and notes that carrier selection research to date has generally suffered from one or more of three problems: (1) because the research has focused on criteria 'importance', it has not identified determinants of purchase behaviour, that is, the 'salience' of different criteria; (2) the research has had sample size problems leading to the need to assume that the market is homogeneous or, less acceptable, that importance ratings will identify usable segments via factor analysis; and (3) carrier perfomance evaluation in conjucation with determinant criteria has largely been ignored. The paper focused on the problems surrounding the second of these by evaluating the relative importance of various service attributes for different geographic and customer dimensions. The paper concludes that the market is definitely not homogeneous in its requirements of carriers and that different elements surface as important both in identifiable geographical markets and customer groups. It also draws a number of conclusions about carrier choice in future and the implications for academic research.     

Real-time capable vehicle-trailer coupling by algorithms for differential-algebraic equations

The real-time simulation of vehicle trains requires an accurate and numerically feasible representation of the vehicle-trailer coupling. Although the equations of motion for the chassis instances can be reduced to systems of ordinary differential equations, additional constraints on the relative motion of vehicle and trailer are introduced when considering the hitch. In this article, we present a strategy for the simulation of vehicle-trailer combinations, where the algebraic constraints of the coupling are treated explicitly. Although this approach allows exact modeling of the respective joint geometry and realistic calculation of the coupling forces, a suitable numerical algorithm is required in order to solve the resulting differential-algebraic system of index 3 in real-time. The implementation in a commercial vehicle dynamics program is discussed and real-time simulation results are shown, which prove its feasibility for different coupling joints and demanding driving maneuvers.     

Estimating probability distributions of dynamic queues

Queues are often associated with uncertainty or unreliability, which can arise from chance or climatic events, phase changes in system behaviour, or inherent randomness. Knowing the probability distribution of the number of customers in a queue is important for estimating the risk of stress or disruption to routine services and upstream blocking, potentially leading to exceeding critical limits, gridlock or incidents. The present paper focuses on time-varying queues produced by transient oversaturation during demand peaks where there is randomness in arrivals and service. The objective is to present practical methods for estimating a probability distribution from knowledge of the mean, variance and utilisation (degree of saturation) of a queue available from computationally efficient, if approximate, time-dependent calculation. This is made possible by a novel expression for time-dependent queue variance. The queue processes considered are those commonly used to represent isolated priority (M/M/1) and signal-like (M/D/1) systems, plus some statistical variations within the common Pollaczek-Khinchin framework. Results are verified by comparison with Markov simulation based on recurrence relations.     

Control Concepts for Facilitating Motorway On-ramp Merging Using Intelligent Vehicles

Abstract

Congestion at motorway junctions is a traffic phenomenon that degrades operation of infrastructure and can lead to breakdown of traffic flow and associated reduction in capacity. Advanced communication technologies open new possibilities to prevent or at least delay this phenomenon, and innovative active traffic management systems have been developed in the recent years for better control of motorway traffic. This paper presents a review of control strategies for facilitating motorway on-ramp merging using intelligent vehicles. First, the concepts of the control algorithms are reviewed chronologically divided into three types of intelligent vehicle: completely automated, equipped with cooperative adaptive cruise control and equipped with on-board display. Then, a common structure is identified, and the algorithms are presented based on their characteristics in order to identify similarities, dissimilarities, trends and possible future research directions. Finally, using a similar approach, a review of the methods used to evaluate these control strategies identifies important aspects that should be considered by further research on this topic.     

Editorial: maritime issues in the Americas

Part 2 of this paper deals with the variety of ro-ro cargo-handling methods employed in Marseilles, and considers the hinterlands and land transport links with the ro-ro services of the port     

Applying a Mediated Negotiation Framework to Integrated Coastal Zone Management

Conflict is intrinsic to coastal zone management, yet relatively few peer-reviewed studies have examined how coastal managers might apply conflict resolution processes in the coastal zone management (CZM) context. The authors believe that many of these disputes can be addressed by using a structured mediation model that involves face-to-face negotiation with a broad range of stakeholders to build consensus-based agreements for integrated coastal zone management (ICZM). To explore this further, the article examines four questions. First, it examines how CZM literature characterizes conflict and conflict resolution. Second, it looks at how essential principles from the field of alternative dispute resolution and environmental mediation can be best employed in the ICZM context. In particular, it explores the various elements of a stepwise agreement building model, a mediated negotiation process model the authors use in practice that bases its success on a foundation of four principles: representation, participation, legitimacy, and accountability. Next, it details three essential tools used in this process, stakeholder analysis, joint factfinding, and single-text negotiation, that the authors believe to be promising for developing and adopting stable, well-informed, and implementable agreements for ICZM. Finally, the article examines how these structuring principles and process strategies have been used in two recent case studies regarding the management of the San Francisco estuary and its tributaries.     

Equilibrium analysis of the scheduling of tours in congested networks

In this paper, we develop a model of travel in tours that joins several locations by travel through a congested network. We develop a microscopic analysis in continuous time of individual benefits obtained by spending time at each of the locations and costs incurred through travel between them. This is combined with a continuous time macroscopic equilibrium model of travel during congested peak periods to show how individuals' travel choices are influenced by the congestion that result from corresponding choices made by others. We show how different travellers can achieve identical net utilities by making different combinations of choices within the equilibrium. The resulting model can be used to investigate the effect on travel behaviour and individual utility of various transport interventions, and we illustrate this by considering the effect of a peak‐period charge that eliminates congestion.     

Improved velocity estimation using single loop detectors

This paper develops an improved algorithm for estimating velocity from single loop detector data. Unlike preceding works, the algorithm is simple enough that it can be implemented using existing controller hardware. The discussion shows how the benefits of this work extend to automated tests of detector data quality at dual loop speed traps. Finally, this paper refutes an earlier study that found conventional single loop velocity estimates are biased.     

Improving the validity and reliability of authentic assessment in seafarer education and training: a conceptual and practical framework to enhance resulting assessment outcomes

Past literature on authentic assessment suggests that it provides a far more reliable and valid indicator of outcomes such as higher student engagement, ability to transfer skills to different contexts, multiple evidence of competence, and student performance. This has appeal in seafarer education and training where both students and employers increasingly perceive traditional assessment methods as failing to consistently generate these outcomes. However, this paper argues that improving different aspects of assessment validity and reliability is essentially required to enhance the outcomes identified above. The paper builds on and extends previous work to investigate and develop a conceptual and practical framework that promotes a holistic approach to authentic assessment that provides greater assurances of validity and reliability throughout all stages of assessment within seafarer programs. It also lays the path to future research directions by establishing the agenda to test the practicality of the framework in the authentic assessment of seafarer students and also investigate the impact of students’ perception of increasing authenticity on performance scores in assessment tasks.