124,659 research outputs found
Equilibrium analysis of trip chains in congested networks
No full textIn this paper, we develop a model of travel in a chain of trips joining several locations througha congested network. We develop a microscopic analysis of individual benefits obtained byspending time at each of the locations and costs incurred through travel between them. This iscombined with a macroscopic equilibrium model of travel during congested peak periods toshow how individuals? travel choices are influenced by the congestion that result fromcorresponding choices made by others. We show how different travellers can achieveidentical net utilities by making different combinations of choices within the equilibrium. Theresulting model can be used to investigate the effect on travel behaviour and individual utilityof various transport interventions, and we illustrate this by considering the effect of a peakperiodcharge that eliminates congestion
Video vehicle detection at signalised junctions: a simulation-based study
No full textMany existing advanced methods of traffic signal control depend on information about
approaching traffic provided by inductive loop detectors at particular points in the road. But
analysis of images from CCTV cameras can in principle provide more comprehensive
information about traffic approaching and passing through junctions, and cameras may be
easier to install and maintain than loop detectors, and some systems based on video detection
have already been in use for some time.
Against this background, computer simulation has been used to explore the potential of
existing and immediately foreseeable capability in automatic on-line image analysis to extract
information relevant to signal control from images provided by cameras mounted in
acceptable positions at signal-controlled junctions. Some consequences of extracting relevant
information in different ways were investigated in the context of an existing detailed
simulation model of vehicular traffic moving through junctions under traffic-responsive signal
control, and the development of one basic and one advanced algorithm for traffic-responsive
control. The work was confined as a first step to operation of one very simple signalcontrolled
junction.
Two techniques for extraction of information from images were modelled - a more ambitious
technique based on distinguishing most of the individual vehicles visible to the camera, and a
more modest technique requiring only that the presence of vehicles in any part of the image
be distinguished from the background scene. In the latter case, statistical modelling was used
to estimate the number of vehicles corresponding to any single area of the image that
represents vehicles rather than background.
At the simple modelled junction, each technique of extraction enabled each of the algorithms
for traffic-responsive control of the signals to achieve average delays per vehicle appreciably
lower than those given by System D control, and possibly competitive with those that MOVA
would give, but comparison with MOVA was beyond the scope of the initial study.
These results of simulation indicate that image analysis of CCTV pictures should be able to
provide sufficient information in practice for traffic-responsive control that is competitive
with existing techniques. Ways in which the work could be taken further were discussed with
practitioners, but have not yet been progressed
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Adaptive signal control using approximate dynamic programming
No full textThis paper presents a concise summary of a study on adaptive traffic signal controller for real time operation. The adaptive controller is designed to achieve three operational objectives: first, the controller adopts a dual control principle to achieve a balanced influence between immediate cost and long-term cost in operation; second, controller switches signals without referring to a preset plan and is acyclic; third, controller adjusts its parameters online to adapt new environment. Not all of these features are available in existing operational controllers. Although dynamic programming (DP) is the only exact solution for achieving the operational objectives, it is usually impractical for real time operation because of demand in computation and information. To circumvent the difficulties, we use approximate dynamic programming (ADP) in conjunction with online learning techniques. This approach can substantially reduce computational burden by replacing the exact value function of DP with a continuous linear approximation function, which is then updated progressively by online learning techniques. Two online learning techniques, which are reinforcement learning and monotonicity approximation respectively, are investigated. We find in computer simulation that the ADP controller leads to substantial savings in vehicle delays in comparison with optimised fixed-time plans. The implications of this study to traffic control are: the ADP controller meet all of the three operational objectives with competitive results, and can be readily implemented for operations at both isolated intersection and traffic networks; the ADP algorithm is computationally efficient, and the ADP controller is an evolving system that requires minimum human intervention; the ADP technique offers a flexible theoretical framework in which a range of functional forms and learning techniques can be further studied
System optimal traffic assignment with departure time choice
No full textThis thesis investigates analytical dynamic system optimal assignment with departure time
choice in a rigorous and original way. Dynamic system optimal assignment is formulated here
as a state-dependent optimal control problem. A fixed volume of traffic is assigned to
departure times and routes such that the total system travel cost is minimized. Although the
system optimal assignment is not a realistic representation of traffic, it provides a bound on
performance and shows how the transport planner or engineer can make the best use of the
road system, and as such it is a useful benchmark for evaluating various transport policy
measures. The analysis shows that to operate the transport system optimally, each traveller in
the system should consider the dynamic externality that he or she imposes on the system from
the time of his or her entry. To capture this dynamic externality, we develop a novel
sensitivity analysis of travel cost. Solution algorithms are developed to calculate the dynamic
externality and traffic assignments based on the analyses. We also investigate alternative
solution strategies and the effect of time discretization on the quality of calculated
assignments. Numerical examples are given and the characteristics of the results are discussed.
Calculating dynamic system optimal assignment and the associated optimal toll could be too
difficult for practical implementation. We therefore consider some practical tolling strategies
for dynamic management of network traffic. The tolling strategies considered in this thesis
include both uniform and congestion-based tolling strategies, which are compared with the
dynamic system optimal toll so that their performance can be evaluated. In deriving the
tolling strategies, it is assumed that we have an exact model for the underlying traffic
behaviour. In reality, we do not have such information so that the robustness of a toll
calculation method is an important issue to be investigated in practice. It is found that the
tolls calculated by using divided linear traffic models can perform well over a wide range of
scenarios. The divided linear travel time models thus should receive more attention in the
future research on robust dynamic traffic control strategies design. In conclusion, this thesis
contributes to the literature on dynamic traffic modelling and management, and to support
further analysis and model development in this area
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
On the Treatment of Repeated Observations in Panel Data: Efficiency of Mixed Logit Parameter Estimates
No full textPanel data with repeated observations, Discrete choice models, Parameter efficiency,
Landau-Lifshitz-Navier-Stokes Equations: Large Deviations and Relationship to The Energy Equality
No full textGess B, Heydecker D, Wu Z. Landau-Lifshitz-Navier-Stokes Equations: Large Deviations and Relationship to The Energy Equality. arXiv:2311.02223. 2023.The dynamical large deviations principle for the three-dimensional
incompressible Landau-Lifschitz-Navier-Stokes equations is shown, in the joint
scaling regime of vanishing noise intensity and correlation length. This proves
the consistency of the large deviations in lattice gas models \cite{QY}, with
Landau-Lifschitz fluctuating hydrodynamics \cite{LL87}. Secondly, in the course
of the proof, we unveil a novel relation between the validity of the
deterministic energy equality for the deterministic forced Navier-Stokes
equations and matching large deviations upper and lower bounds. In particular,
we conclude that time-reversible uniqueness to the forced Navier-Stokes
equations implies the validity of the energy equality, thus generalising the
classical Lions-Ladyzhenskaya result. Thirdly, we prove that no non-trivial
large deviations result can be true for local-in-time strong solutions
On the treatment of the repeated observations in panel data: efficiency of Mixed Logit parameter estimates
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