745 research outputs found
Upper Bounds for the Critical Car Densities in Traffic Flow Problems
In most models of traffic flow, the car density is the only free
parameter in determining the average car velocity . The
critical car density , which is defined to be the car density separating
the jamming phase (with ) and the moving phase (with
), is an important physical quantity to investigate. By
means of simple statistical argument, we show that for the
Biham-Middleton-Levine model of traffic flow in two or higher spatial
dimensions. In particular, we show that in 2 dimension and
in () dimensions.Comment: REVTEX 3.0, 5 pages with 1 figure appended at the back, Minor
revision, to be published in the Sept issue of J.Phys.Soc.Japa
Two Lane Traffic Simulations using Cellular Automata
We examine a simple two lane cellular automaton based upon the single lane CA
introduced by Nagel and Schreckenberg. We point out important parameters
defining the shape of the fundamental diagram. Moreover we investigate the
importance of stochastic elements with respect to real life traffic.Comment: to be published in Physica A, 19 pages, 9 out of 13 postscript
figures, 24kB in format .tar.gz., 33kB in format .tar.gz.uu, for a full
version including all figures see
http://studguppy.tsasa.lanl.gov/research_team/papers
Spontaneous Time Asymmetry due to Horizon
We show that quantized matter fields in the presence of background metrics
with Horizon exhibit spontaneous time asymmetry. All quantized matter fields
have to vanish at the horizon. Some phenemenological applications of this in
the context of black holes and early universe are considered.Comment: 4 pages, Revte
Anisotropic effect on two-dimensional cellular automaton traffic flow with periodic and open boundaries
By the use of computer simulations we investigate, in the cellular automaton
of two-dimensional traffic flow, the anisotropic effect of the probabilities of
the change of the move directions of cars, from up to right () and from
right to up (), on the dynamical jamming transition and velocities
under the periodic boundary conditions in one hand and the phase diagram under
the open boundary conditions in the other hand. However, in the former case,
the first order jamming transition disappears when the cars alter their
directions of move ( and/or ). In the open boundary
conditions, it is found that the first order line transition between jamming
and moving phases is curved. Hence, by increasing the anisotropy, the moving
phase region expand as well as the contraction of the jamming phase one.
Moreover, in the isotropic case, and when each car changes its direction of
move every time steps (), the transition from the jamming
phase (or moving phase) to the maximal current one is of first order.
Furthermore, the density profile decays, in the maximal current phase, with an
exponent .}Comment: 13 pages, 22 figure
Towards a variational principle for motivated vehicle motion
We deal with the problem of deriving the microscopic equations governing the
individual car motion based on the assumptions about the strategy of driver
behavior. We suppose the driver behavior to be a result of a certain compromise
between the will to move at a speed that is comfortable for him under the
surrounding external conditions, comprising the physical state of the road, the
weather conditions, etc., and the necessity to keep a safe headway distance
between the cars in front of him. Such a strategy implies that a driver can
compare the possible ways of his further motion and so choose the best one. To
describe the driver preferences we introduce the priority functional whose
extremals specify the driver choice. For simplicity we consider a single-lane
road. In this case solving the corresponding equations for the extremals we
find the relationship between the current acceleration, velocity and position
of the car. As a special case we get a certain generalization of the optimal
velocity model similar to the "intelligent driver model" proposed by Treiber
and Helbing.Comment: 6 pages, RevTeX
A Cellular Automaton Model for Bi-Directionnal Traffic
We investigate a cellular automaton (CA) model of traffic on a bi-directional
two-lane road. Our model is an extension of the one-lane CA model of {Nagel and
Schreckenberg 1992}, modified to account for interactions mediated by passing,
and for a distribution of vehicle speeds. We chose values for the various
parameters to approximate the behavior of real traffic. The density-flow
diagram for the bi-directional model is compared to that of a one-lane model,
showing the interaction of the two lanes. Results were also compared to
experimental data, showing close agreement. This model helps bridge the gap
between simplified cellular automata models and the complexity of real-world
traffic.Comment: 4 pages 6 figures. Accepted Phys Rev
Optimizing Traffic Lights in a Cellular Automaton Model for City Traffic
We study the impact of global traffic light control strategies in a recently
proposed cellular automaton model for vehicular traffic in city networks. The
model combines basic ideas of the Biham-Middleton-Levine model for city traffic
and the Nagel-Schreckenberg model for highway traffic. The city network has a
simple square lattice geometry. All streets and intersections are treated
equally, i.e., there are no dominant streets. Starting from a simple
synchronized strategy we show that the capacity of the network strongly depends
on the cycle times of the traffic lights. Moreover we point out that the
optimal time periods are determined by the geometric characteristics of the
network, i.e., the distance between the intersections. In the case of
synchronized traffic lights the derivation of the optimal cycle times in the
network can be reduced to a simpler problem, the flow optimization of a single
street with one traffic light operating as a bottleneck. In order to obtain an
enhanced throughput in the model improved global strategies are tested, e.g.,
green wave and random switching strategies, which lead to surprising results.Comment: 13 pages, 10 figure
Alpha-particle-induced breakup of the deuteron
Alpha-particle-induced deuteron breakup reactions have been studied in single-counter measurements at incident alpha-particle energies of 41.6 and 29.3 MeV. Simultaneous differential and total cross-section measurements have been carried out on protons, deuterons, and alpha particles. Unambiguous evidence for final-state resonance effects in the alpha-nucleon interactions have been obtained, particularly from the proton energy spectra; the p3/2 alpha-nucleon resonances corresponding to the He5 and Li5 ground states play important roles. As anticipated, phase-space-factor and zero-range Born-approximation calculations failed to reproduce the observed energy spectra. A more exact analysis which explicitly includes the alpha-nucleon interactions, represented by Gammel-Thaler phenomenological potentials, does provide good agreement with the experimental results both in spectrum shape and in total breakup cross section
Experiences with a simplified microsimulation for the Dallas/Fort Worth area
We describe a simple framework for micro simulation of city traffic. A medium
sized excerpt of Dallas was used to examine different levels of simulation
fidelity of a cellular automaton method for the traffic flow simulation and a
simple intersection model. We point out problems arising with the granular
structure of the underlying rules of motion.Comment: accepted by Int.J.Mod.Phys.C, 20 pages, 14 figure
The Effect Of Delay Times On The Optimal Velocity Traffic Flow Behavior
We have numerically investigated the effect of the delay times and
of a mixture of fast and slow vehicles on the fundamental diagram of
the optimal velocity model. The optimal velocity function of the fast cars
depends not only on the headway of each car but also on the headway of the
immediately preceding one. It is found that the small delay times have almost
no effects, while, for sufficiently large delay time the current
profile displays qualitatively five different forms depending on ,
and the fractions and of the fast and slow cars
respectively. The velocity (current) exhibits first order transitions at low
and/or high densities, from freely moving phase to the congested state, and
from congested state to the jamming one respectively accompanied by the
existence of a local minimal current. Furthermore, there exist a critical value
of above which the metastability and hysteresis appear. The
spatial-temporal traffic patterns present more complex structur
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