2,400 research outputs found
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.
The asymmetric exclusion process: Comparison of update procedures
The asymmetric exclusion process (ASEP) has attracted a lot of interest not
only because its many applications, e.g. in the context of the kinetics of
biopolymerization and traffic flow theory, but also because it is a
paradigmatic model for nonequilibrium systems. Here we study the ASEP for
different types of updates, namely random-sequential, sequential,
sublattice-parallel and parallel. In order to compare the effects of the
different update procedures on the properties of the stationary state, we use
large-scale Monte Carlo simulations and analytical methods, especially the
so-called matrix-product Ansatz (MPA). We present in detail the exact solution
for the model with sublattice-parallel and sequential updates using the MPA.
For the case of parallel update, which is important for applications like
traffic flow theory, we determine the phase diagram, the current, and density
profiles based on Monte Carlo simulations. We furthermore suggest a MPA for
that case and derive the corresponding matrix algebra.Comment: 47 pages (11 PostScript figures included), LATEX, Two misprints in
equations correcte
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
Metastable States in Cellular Automata for Traffic Flow
Measurements on real traffic have revealed the existence of metastable states
with very high flow. Such states have not been observed in the
Nagel-Schreckenberg (NaSch) model which is the basic cellular automaton for the
description of traffic. Here we propose a simple generalization of the NaSch
model by introducing a velocity-dependent randomization. We investigate a
special case which belongs to the so-called slow-to-start rules. It is shown
that this model exhibits metastable states, thus sheding some light on the
prerequisites for the occurance of hysteresis effects in the flow-density
relation.Comment: 15 pages, 8 ps-figures included; accepted for publication in EPJ
Particle interactions and lattice dynamics: Scenarios for efficient bidirectional stochastic transport?
Intracellular transport processes driven by molecular motors can be described
by stochastic lattice models of self-driven particles. Here we focus on
bidirectional transport models excluding the exchange of particles on the same
track. We explore the possibility to have efficient transport in these systems.
One possibility would be to have appropriate interactions between the various
motors' species, so as to form lanes. However, we show that the lane formation
mechanism based on modified attachment/detachment rates as it was proposed
previously is not necessarily connected to an efficient transport state and is
suppressed when the diffusivity of unbound particles is finite. We propose
another interaction mechanism based on obstacle avoidance that allows to have
lane formation for limited diffusion. Besides, we had shown in a separate paper
that the dynamics of the lattice itself could be a key ingredient for the
efficiency of bidirectional transport. Here we show that lattice dynamics and
interactions can both contribute in a cooperative way to the efficiency of
transport. In particular, lattice dynamics can decrease the interaction
threshold beyond which lanes form. Lattice dynamics may also enhance the
transport capacity of the system even when lane formation is suppressed.Comment: 25 pages, 17 figures, 2 table
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