17,232 research outputs found
Macroscopic Dynamics of Multi-Lane Traffic
We present a macroscopic model of mixed multi-lane freeway traffic that can
be easily calibrated to empirical traffic data, as is shown for Dutch highway
data. The model is derived from a gas-kinetic level of description, including
effects of vehicular space requirements and velocity correlations between
successive vehicles. We also give a derivation of the lane-changing rates. The
resulting dynamic velocity equations contain non-local and anisotropic
interaction terms which allow a robust and efficient numerical simulation of
multi-lane traffic. As demonstrated by various examples, this facilitates the
investigation of synchronization patterns among lanes and effects of on-ramps,
off-ramps, lane closures, or accidents.Comment: For related work see
http://www.theo2.physik.uni-stuttgart.de/helbing.htm
Conductance noise in interacting Anderson insulators driven far from equilibrium
The combination of strong disorder and many-body interactions in Anderson
insulators lead to a variety of intriguing non-equilibrium transport phenomena.
These include slow relaxation and a variety of memory effects characteristic of
glasses. Here we show that when such systems are driven with sufficiently high
current, and in liquid helium bath, a peculiar type of conductance noise can be
observed. This noise appears in the conductance versus time traces as
downward-going spikes. The characteristic features of the spikes (such as
typical width) and the threshold current at which they appear are controlled by
the sample parameters. We show that this phenomenon is peculiar to hopping
transport and does not exist in the diffusive regime. Observation of
conductance spikes hinges also on the sample being in direct contact with the
normal phase of liquid helium; when this is not the case, the noise exhibits
the usual 1/f characteristics independent of the current drive. A model based
on the percolative nature of hopping conductance explains why the onset of the
effect is controlled by current density. It also predicts the dependence on
disorder as confirmed by our experiments. To account for the role of the bath,
the hopping transport model is augmented by a heuristic assumption involving
nucleation of cavities in the liquid helium in which the sample is immersed.
The suggested scenario is analogous to the way high-energy particles are
detected in a Glaser's bubble chamber.Comment: 15 pages 22 figure
Single-Bottleneck Approximation for Driven Lattice Gases with Disorder and Open Boundary Conditions
We investigate the effects of disorder on driven lattice gases with open
boundaries using the totally asymmetric simple exclusion process as a
paradigmatic example. Disorder is realized by randomly distributed defect sites
with reduced hopping rate. In contrast to equilibrium, even macroscopic
quantities in disordered non-equilibrium systems depend sensitively on the
defect sample. We study the current as function of the entry and exit rates and
the realization of disorder and find that it is, in leading order, determined
by the longest stretch of consecutive defect sites (single-bottleneck
approximation, SBA). Using results from extreme value statistics the SBA allows
to study ensembles with fixed defect density which gives accurate results, e.g.
for the expectation value of the current. Corrections to SBA come from
effective interactions of bottlenecks close to the longest one. Defects close
to the boundaries can be described by effective boundary rates and lead to
shifts of the phase transitions. Finally it is shown that the SBA also works
for more complex models. As an example we discuss a model with internal states
that has been proposed to describe transport of the kinesin KIF1A.Comment: submitted to J. Stat. Mec
Pedestrian, Crowd, and Evacuation Dynamics
This contribution describes efforts to model the behavior of individual
pedestrians and their interactions in crowds, which generate certain kinds of
self-organized patterns of motion. Moreover, this article focusses on the
dynamics of crowds in panic or evacuation situations, methods to optimize
building designs for egress, and factors potentially causing the breakdown of
orderly motion.Comment: This is a review paper. For related work see http://www.soms.ethz.c
Congested Traffic States in Empirical Observations and Microscopic Simulations
We present data from several German freeways showing different kinds of
congested traffic forming near road inhomogeneities, specifically lane
closings, intersections, or uphill gradients. The states are localized or
extended, homogeneous or oscillating. Combined states are observed as well,
like the coexistence of moving localized clusters and clusters pinned at road
inhomogeneities, or regions of oscillating congested traffic upstream of nearly
homogeneous congested traffic. The experimental findings are consistent with a
recently proposed theoretical phase diagram for traffic near on-ramps [D.
Helbing, A. Hennecke, and M. Treiber, Phys. Rev. Lett. {\bf 82}, 4360 (1999)].
We simulate these situations with a novel continuous microscopic single-lane
model, the ``intelligent driver model'' (IDM), using the empirical boundary
conditions. All observations, including the coexistence of states, are
qualitatively reproduced by describing inhomogeneities with local variations of
one model parameter.
We show that the results of the microscopic model can be understood by
formulating the theoretical phase diagram for bottlenecks in a more general
way. In particular, a local drop of the road capacity induced by parameter
variations has practically the same effect as an on-ramp.Comment: Now published in Phys. Rev. E. Minor changes suggested by a referee
are incorporated; full bibliographic info added. For related work see
http://www.mtreiber.de/ and http://www.helbing.org
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