5,296 research outputs found
Self-organization of traffic jams in cities: effects of stochastic dynamics and signal periods
We propose a cellular automata model for vehicular traffic in cities by
combining (and appropriately modifying) ideas borrowed from the
Biham-Middleton-Levine (BML) model of city traffic and the Nagel-Schreckenberg
(NS) model of highway traffic. We demonstrate a phase transition from the
"free-flowing" dynamical phase to the completely "jammed" phase at a vehicle
density which depends on the time periods of the synchronized signals and the
separation between them. The intrinsic stochasticity of the dynamics, which
triggers the onset of jamming, is similar to that in the NS model, while the
phenomenon of complete jamming through self-organization as well as the final
jammed configurations are similar to those in the BML model. Using our new
model, we have made an investigation of the time-dependence of the average
speeds of the cars in the "free-flowing" phase as well as the dependence of
flux and jamming on the time period of the signals.Comment: 4 pages, REVTEX, 4 eps figures include
Dynamic masses for the close PG1159 binary SDSSJ212531.92-010745.9
SDSSJ212531.92-010745.9 is the first known PG1159 star in a close binary with
a late main sequence companion allowing a dynamical mass determination. The
system shows flux variations with a peak-to-peak amplitude of about 0.7 mag and
a period of about 6.96h. In August 2007, 13 spectra of SDSSJ212531.92-010745.9
covering the full orbital phase range were taken at the TWIN 3.5m telescope at
the Calar Alto Observatory (Alm\'{e}ria, Spain). These confirm the typical
PG1159 features seen in the SDSS discovery spectrum, together with the Balmer
series of hydrogen in emission (plus other emission lines), interpreted as
signature of the companion's irradiated side. A radial velocity curve was
obtained for both components. Using co-added radial-velocity-corrected spectra,
the spectral analysis of the PG1159 star is being refined.
The system's lightcurve, obtained during three seasons of photometry with the
G\"ottingen 50cm and T\"ubingen 80cm telescopes, was fitted with both the
NIGHTFALL and PHOEBE binary simulation programs. An accurate mass determination
of the PG1159 component from the radial velocity measurements requires to first
derive the inclination, which requires light curve modelling and yields further
constraints on radii, effective temperature and separation of the system's
components. From the analysis of all data available so far, we present the
possible mass range for the PG1159 component of SDSSJ212531.92-010745.9.Comment: 8 pages, in "White dwarfs", proceedings of the 16th European White
Dwarf Workshop, eds. E. Garcia-Berro, M. Hernanz, J. Isern, S. Torres, to be
published in J. Phys.: Conf. Se
Performance Evaluation of Road Traffic Control Using a Fuzzy Cellular Model
In this paper a method is proposed for performance evaluation of road traffic
control systems. The method is designed to be implemented in an on-line
simulation environment, which enables optimisation of adaptive traffic control
strategies. Performance measures are computed using a fuzzy cellular traffic
model, formulated as a hybrid system combining cellular automata and fuzzy
calculus. Experimental results show that the introduced method allows the
performance to be evaluated using imprecise traffic measurements. Moreover, the
fuzzy definitions of performance measures are convenient for uncertainty
determination in traffic control decisions.Comment: The final publication is available at http://www.springerlink.co
Coupled-Map Modeling of One-Dimensional Traffic Flow
We propose a new model of one-dimensional traffic flow using a coupled map
lattice. In the model, each vehicle is assigned a map and changes its velocity
according to it. A single map is designed so as to represent the motion of a
vehicle properly, and the maps are coupled to each other through the headway
distance. By simulating the model, we obtain a plot of the flow against the
concentration similar to the observed data in real traffic flows. Realistic
traffic jam regions are observed in space-time trajectories.Comment: 5 postscript figures available upon reques
Towards a Macroscopic Modelling of the Complexity in Traffic Flow
We present a macroscopic traffic flow model that extends existing fluid-like
models by an additional term containing the second derivative of the safe
velocity. Two qualitatively different shapes of the safe velocity are explored:
a conventional Fermi-type function and a function exhibiting a plateau at
intermediate densities. The suggested model shows an extremely rich dynamical
behaviour and shows many features found in real-world traffic data.Comment: submitted to Phys. Rev.
Maxwell Model of Traffic Flows
We investigate traffic flows using the kinetic Boltzmann equations with a
Maxwell collision integral. This approach allows analytical determination of
the transient behavior and the size distributions. The relaxation of the car
and cluster velocity distributions towards steady state is characterized by a
wide range of velocity dependent relaxation scales, , with
the ratio of the passing and the collision rates. Furthermore, these
relaxation time scales decrease with the velocity, with the smallest scale
corresponding to the decay of the overall density. The steady state cluster
size distribution follows an unusual scaling form . This distribution is primarily algebraic, , for , and is exponential otherwise.Comment: revtex, 10 page
Structure and Instability of High-Density Equations for Traffic Flow
Similar to the treatment of dense gases, fluid-dynamic equations for the
dynamics of congested vehicular traffic are derived from Enskog-like kinetic
equations. These contain additional terms due to the anisotropic vehicle
interactions. The calculations are carried out up to Navier-Stokes order. A
linear instability analysis indicates an additional kind of instability
compared to previous macroscopic traffic models. The relevance for describing
granular flows is outlined.Comment: For related work see
http://www.theo2.physik.uni-stuttgart.de/helbing.htm
Mechanical restriction versus human overreaction triggering congested traffic states
A new cellular automaton (CA) traffic model is presented. The focus is on
mechanical restrictions of vehicles realized by limited acceleration and
deceleration capabilities. These features are incorporated into the model in
order to construct the condition of collision-free movement. The strict
collision-free criterion imposed by the mechanical restrictions is softened in
certain traffic situations, reflecting human overreaction. It is shown that the
present model reliably reproduces most empirical findings including
synchronized flow, the so-called {\it pinch effect}, and the time-headway
distribution of free flow. The findings suggest that many free flow phenomena
can be attributed to the platoon formation of vehicles ({\it platoon effect})Comment: 5 pages, 3 figures, to appear in PR
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