The existence, uniqueness and computation of an arc-based dynamic network user equilibrium formulation

In this paper, a dynamic user equilibrium traffic assignment model with simultaneous departure time/route choices and elastic demands is formulated as an arc-based nonlinear complementarity problem on congested traffic networks. The four objectives of this paper are (1) to develop an arc-based formulation which obviates the use of path-specific variables, (2) to establish existence of a dynamic user equilibrium solution to the model using Brouwer's fixed-point theorem, (3) to show that the vectors of total arc inflows and associated minimum unit travel costs are unique by imposing strict monotonicity conditions on the arc travel cost and demand functions along with a smoothness condition on the equilibria, and (4) to develop a heuristic algorithm that requires neither a path enumeration nor a storage of path-specific flow and cost information. Computational results are presented for a simple test network with 4 arcs, 3 nodes, and 2 origin–destination pairs over the time interval of 120 periods.     

An alternative to FASTSIM for tangential solution of the wheel–rail contact

In most rail vehicle dynamics simulation packages, tangential solution of the wheel–rail contact is gained by means of Kalker's FASTSIM algorithm. While 5–25% error is expected for creep force estimation, the errors of shear stress distribution, needed for wheel–rail damage analysis, may rise above 30% due to the parabolic traction bound. Therefore, a novel algorithm named FaStrip is proposed as an alternative to FASTSIM. It is based on the strip theory which extends the two-dimensional rolling contact solution to three-dimensional contacts. To form FaStrip, the original strip theory is amended to obtain accurate estimations for any contact ellipse size and it is combined by a numerical algorithm to handle spin. The comparison between the two algorithms shows that using FaStrip improves the accuracy of the estimated shear stress distribution and the creep force estimation in all studied cases. In combined lateral creepage and spin cases, for instance, the error in force estimation reduces from 18% to less than 2%. The estimation of the slip velocities in the slip zone, needed for wear analysis, is also studied. Since FaStrip is as fast as FASTSIM, it can be an alternative for tangential solution of the wheel–rail contact in simulation packages.     

A comparative study of the emissions by road maintenance works and the disrupted traffic using life cycle assessment and micro-simulation

Life cycle assessment is being accepted by the road industry to measure such key environmental impacts as the energy consumption and carbon footprint of its materials and laying processes. Previous life cycle studies have indicated that the traffic vehicles account for the majority of fuel consumption and emissions from a road. Contractors and road agencies are looking for road maintenance works that have the least overall environmental impact considering both the roadwork itself and the disrupted traffic. We review life cycle assessment studies and describe the development of a model for pavement construction and maintenance, detailing the methodology and data sources. The model is applied to an asphalt pavement rehabilitation project in the UK, and the micro-simulation program VISSIM is used to model the traffic on that road section. The simulation results are fed into a traffic emissions model and emissions from the roadwork and the traffic are compared. The additional fuel consumption and emissions by the traffic during the roadwork are significant. This indicates that traffic management at road maintenance projects should be included in the life cycle assessment analysis of such work.     

Understanding and Modeling the Social Preferences for Riders in Rideshare Matching

Transportation - Ridesharing is the sharing of trip segments from one place to another among multiple travelers, obviating others’ needs to drive themselves. By having more than one occupant...     

30t轴重轮对的研制

介绍了LKAB新型铁矿石货车和机车的技术条件，并阐述了货车和机车用大轴重轮对材料、计算和有关试验。     

Solid Axle and Independently-Rotating Railway Wheelsets - A Control Engineering Assessment of Stability

Block diagram representations of both conventional wheelsets and wheelsets with independently-rotating wheels are developed, with the objective of giving insights from a control engineering viewpoint for studies of actively-controlled wheelsets. The analysis predicts a quasi-kinematic oscillation with independently-rotating wheels which has not been reported before. It also identifies possibilities for control approaches which might be used to stabilise a wheelset without affecting steady-state curving performance.     

Considering “Coastal Carbon” in Existing U.S. Federal Statutes and Policies

Coastal ecosystems such as mangroves, salt marshes, and seagrasses provide important ecosystem services, including nursery habitat for fish, shoreline protection, and the recently recognized service of carbon sequestration and storage. When these wetland ecosystems are degraded or destroyed, the carbon can be released to the atmosphere, where it adds to the concentration of greenhouses gases (GHGs) that contribute to climate change. Many federal statutes and policies specifically require that impacts on ecosystem services be considered in policy implementation. Yet, no federal statute, regulation, or policy accounts directly for the carbon held in coastal habitats. There are a number of federal statutes and policies for which coastal carbon ecosystem services could reasonably be added to environmental and ecosystem considerations already implemented. We look at a subset of these statutes and policies to illustrate how coastal carbon ecosystem services and values might affect the implementation and outcomes of such statutes generally. We identify key steps for the inclusion of the ecosystem services of coastal habitats into the implementation of existing federal policies without statutory changes; doing so would increase the degree to which these policies consider the full economic and ecological impacts of policy actions.     

Comments on 'The limitations of transport policy'

This paper has been written as a response to the paper of Metz (2002) on 'The limitations of transport policy'. It is argued that the issues involved are more complex than Metz implies, and that many current travel patterns stem from decisions made previously about lifestyles, as a result of changing patterns of work, the availability of home-computing facilities, and increasing aspirations and income. Neither the models nor the data sources available to transport planners reflect these trends, and transport policy tends to be simplistic. Many of the transport policy issues stem from increasing car dependency, with its implications, particularly for the elderly and for the young. It is argued that transport policy has not been very effective in the past, and it is likely to be even less so in the future. Hence, there is a need to redefine the role of the transport planner and recognize the limitations of transport policy.     

Quality incentives and quality outcomes in procured public transport - Case study Stockholm

Gross contracts appear to be the most common contract form for procured public transport in Sweden and elsewhere. This contract form, it has been argued, gives weak incentives for operators to deliver the desired quality level. Therefore many procuring public transport authorities amend contracts with quality incentives.This paper examines how such quality incentives influence quality outcomes with focus on cancelled departures and delays. The main findings are that the introduction of quality incentives are correlated with both increases and decreases of measured quality outcomes.We hypothesise that the results are driven by underlying cost changes for achieving desired quality objectives that exceed the possible revenues from the incentives. In interviews with the Stockholm public transport authority (SL) and some operators, two central observations surface. The first is that there are causes for quality failures that are not solely the responsibility of operators and that these are therefore not fully reached by the incentives, and the second is that the operators believe that they have exhausted what they can do under the current contracts.     

Active Yaw Relaxation For Improved Bogie Performance

The use of controlled traction rods to give active yaw relaxation of coned wheelsets is investigated, and is shown to give significant improvements in curving performance without compromising stability, even on curves for which there is flange contact. An assessment of practical implications such as power, actuator and control requirements is included.