382 research outputs found
On the existence of a variational principle for deterministic cellular automaton models of highway traffic flow
It is shown that a variety of deterministic cellular automaton models of
highway traffic flow obey a variational principle which states that, for a
given car density, the average car flow is a non-decreasing function of time.
This result is established for systems whose configurations exhibits local jams
of a given structure. If local jams have a different structure, it is shown
that either the variational principle may still apply to systems evolving
according to some particular rules, or it could apply under a weaker form to
systems whose asymptotic average car flow is a well-defined function of car
density. To establish these results it has been necessary to characterize among
all number-conserving cellular automaton rules which ones may reasonably be
considered as acceptable traffic rules. Various notions such as free-moving
phase, perfect and defective tiles, and local jam play an important role in the
discussion. Many illustrative examples are given.Comment: 19 pages, 4 figure
Car-oriented mean-field theory for traffic flow models
We present a new analytical description of the cellular automaton model for
single-lane traffic. In contrast to previous approaches we do not use the
occupation number of sites as dynamical variable but rather the distance
between consecutive cars. Therefore certain longer-ranged correlations are
taken into account and even a mean-field approach yields non-trivial results.
In fact for the model with the exact solution is reproduced. For
the fundamental diagram shows a good agreement with results from
simulations.Comment: LaTex, 10 pages, 2 postscript figure
Quantitative analysis of pedestrian counterflow in a cellular automaton model
Pedestrian dynamics exhibits various collective phenomena. Here we study
bidirectional pedestrian flow in a floor field cellular automaton model. Under
certain conditions, lane formation is observed. Although it has often been
studied qualitatively, e.g., as a test for the realism of a model, there are
almost no quantitative results, neither empirically nor theoretically. As basis
for a quantitative analysis we introduce an order parameter which is adopted
from the analysis of colloidal suspensions. This allows to determine a phase
diagram for the system where four different states (free flow, disorder, lanes,
gridlock) can be distinguished. Although the number of lanes formed is
fluctuating, lanes are characterized by a typical density. It is found that the
basic floor field model overestimates the tendency towards a gridlock compared
to experimental bounds. Therefore an anticipation mechanism is introduced which
reduces the jamming probability.Comment: 11 pages, 12 figures, accepted for publication in Phys. Rev.
Generalized Centrifugal Force Model for Pedestrian Dynamics
A spatially continuous force-based model for simulating pedestrian dynamics
is introduced which includes an elliptical volume exclusion of pedestrians. We
discuss the phenomena of oscillations and overlapping which occur for certain
choices of the forces. The main intention of this work is the quantitative
description of pedestrian movement in several geometries. Measurements of the
fundamental diagram in narrow and wide corridors are performed. The results of
the proposed model show good agreement with empirical data obtained in
controlled experiments.Comment: 10 pages, 14 figures, accepted for publication as a Regular Article
in Physical Review E. This version contains minor change
Cluster formation and anomalous fundamental diagram in an ant trail model
A recently proposed stochastic cellular automaton model ({\it J. Phys. A 35,
L573 (2002)}), motivated by the motions of ants in a trail, is investigated in
detail in this paper. The flux of ants in this model is sensitive to the
probability of evaporation of pheromone, and the average speed of the ants
varies non-monotonically with their density. This remarkable property is
analyzed here using phenomenological and microscopic approximations thereby
elucidating the nature of the spatio-temporal organization of the ants. We find
that the observations can be understood by the formation of loose clusters,
i.e. space regions of enhanced, but not maximal, density.Comment: 11 pages, REVTEX, with 11 embedded EPS file
Effect of on- and off-ramps in cellular automata models for traffic flow
We present results on the modeling of on- and off-ramps in cellular automata
for traffic flow, especially the Nagel-Schreckenberg model. We study two
different types of on-ramps that cause qualitatively the same effects. In a
certain density regime one observes plateau formation in the fundamental
diagram. The plateau value depends on the input-rate of cars at the on-ramp.
The on-ramp acts as a local perturbation that separates the system into two
regimes: A regime of free flow and another one where only jammed states exist.
This phase separation is the reason for the plateau formation and implies a
behaviour analogous to that of stationary defects. This analogy allows to
perform very fast simulations of complex traffic networks with a large number
of on- and off-ramps because one can parametrise on-ramps in an exceedingly
easy way.Comment: 11 pages, 9 figures, accepted for publication in Int. J. Mod. Phys.
Disorder Effects in CA-Models for Traffic Flow
We investigate the effect of quenched disorder in the Nagel-Schreckenberg
model of traffic flow. Spatial inhomogenities, i.e. lattice sites where the
braking probability is enlarged, are considered as well as particle disorder,
i.e. cars of a different maximum velocity. Both types of disorder lead to
segregated states.Comment: 6 pages, 4 postscript figures, Proceedings of the conference "Traffic
and Granular Flow '97", Duisburg, Germany, October 5-8, 199
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