1,720,961 research outputs found
"Review of models combining traffic assignment and signal control"
No full textThe author reviews a class of models that combine equilibrium traffic assignment and intersection control into a single analysis framework under the assumption of flow-responsive signal settings. The most unique feature of the models is their capacity to consider explicitly the mutual interactions between signal control policies and user route choices--interactions that are usually disregarded in ordinary traffic assignment models and in everyday traffic engineering practice. After describing the combined traffic assignment and control problem, and reviewing alternative formulas and solution algorithms, a discussion is presented on the possible approaches to modeling the various types of link interactions that emerge from the combined use of intersections by competing traffic movements. The author addresses important conceptual issues and implementation aspects, including potential policy implications. The key finding of the survey is that, while the theoretical properties of combined traffic assignment and control models have been extensively studied for two decades and are now well understood, a lack of empirical results and real-world applications are evident, which is necessary to promote the transfer of this modeling approach from research to professional practice
Day-to-day dynamics in a simple traffic network with mixed direct and contrarian route choice behaviors
Full text linkContrarian behavior is an attitude leading individuals to act ‘‘contrary to the crowd’’ and
can be observed in a variety of collective systems. The aim of this study is to investigate
the effects of such behavioral trait on the day-to-day evolution of a traffic system in a
simple two-route scenario. To this end, we formulate a nonlinear, discrete-time dynamical system and analyze how the fraction of contrarian-like choices affects fixed point
uniqueness and stability, as well as mean travel cost evaluated both for the network
as a whole and separately for subjects adopting either type of route choice behavior.
We show that uniqueness and stability of the fixed point of the dynamical system are
ensured inside certain ranges of the fraction of contrarian subjects within the traveling
population, and that the width of such ranges depends on the sensitivity of actual costs
to flows and on the level of accuracy of individuals’ cost perception. Moreover, instability
is seen to take different forms (oscillatory behavior or convergence to alternate fixed
points) depending on which limit of the stability region is crossed by the fraction of
contrarians. Results of the analysis also indicate that introducing memory and learning
in the process of expected cost formation tends to counter the destabilizing effect of
strongly flow-dependent costs and highly cost-sensitive route choices. Finally, direct
and contrarian travelers attain the same mean travel cost throughout the fixed point
stability region, while a competitive advantage of the minority group emerges outside
such region, albeit at the price of a deteriorated global network performance. Overall,
the findings of the study support the conclusion that a well-balanced diversification of
the traveling population in terms of direct and contrarian route choice attitudes has the
potential to protect the system against instabilities induced by other behavioral and
network features, and that this beneficial effect can be amplified by the occurrence
of learning in the formation of perceived travel costs. It is suggested that contrarian
behavior may contribute to mitigating the adverse effects of concentration of choices on
the ‘‘best’’ routes and overreaction to the supplied information, induced by Advanced
Traveler Information Systems, and thus should be explicitly considered in the design of
traffic management strategies involving the deployment of such systems
Combined Dynamics of Route Choice and Gap Acceptance in Road Networks with Priority Intersections
Full text linkA key determinant of the capacity of unsignalized intersection approaches operating under priority control is the gap acceptance behavior of drivers. The parameter commonly used to characterize this behavior is the critical gap, which is the minimum time interval in the priority traffic stream that minor road drivers consider acceptable to safely execute the desired maneuver. When the operation of priority intersections is considered in a network-wide perspective, the analysis of the interaction between gap acceptance behavior and route choice emerges as a compelling research question. This paper proposes a model of the day-to-day dynamics arising from this interaction when the critical gap of minor road drivers is treated as an endogenous variable. We formulate a discrete-time, deterministic nonlinear dynamical system in which the critical gap depends on the traffic flow on the major road. After providing a general formulation of the model, an explicit analysis of fixed-point stability is carried out for an elementary network. Numerical results obtained from the implementation on two example networks suggest that the evolutionary dynamics of the system are affected by the relationship between the critical gap and major road flow. We conclude that, upon proper calibration of the variable critical gap formulation on observed driver behavior, the proposed model has the potential to deliver improved estimates of intersection approach capacities, delays and queue lengths to be used for policy evaluation in a dynamic perspective
Regression analysis with compositional data using orthogonal log-ratio coordinates
No full textCompositional data frequently arise when data refer to components which are proportions or fractions of a whole. Within the log-ratio approach, the analysis of compositional data can be conducted in terms of log-ratio transformations of components. These transformations make it possible to overcome the problem of the constant-sum constraint, making standard statistical methods applicable. In the present work, the log-ratio approach based on orthogonal log-ratio coordinates is adopted to show how it can lead to considerable improvements in the interpretation of the results of regression modeling with compositional data, both as explanatory or response variables. In order to demonstrate its practical usefulness, the methodology presented in this paper is applied to the analysis of air pollution produced by vehicles traveling through road intersections, with a specific focus on the effect of the type of traffic control (traffic signal vs. roundabout) on CO2 emissions
Gap-acceptance behavior at roundabouts: Validation of a driving simulator environment using field observations
Full text linkA general procedure for the validation of a driving simulation environment for the analysis of gap-acceptance behavior was developed in this study. It allows to test whether a synthetic indicator of gap-acceptance behavior (the mean critical gap) shows significant differences when computed on the basis of field observations versus observations collected in the simulated environment. If such differences are not significant, driver behavior can be considered similar in the two contexts, thus supporting validation of the driving simulation environment. In order to demonstrate its effectiveness, the proposed procedure is applied to the case of a three-leg roundabout located in the Veneto region (Italy). The results show that the mean critical gap estimated in the field and the mean critical gap estimated in the virtual environment are not significantly different. The proposed procedure can be applied in various contexts in which gap-acceptance behavior is a central element in terms of safety and operational performance of the traffic system under analysis
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
- …
