Abdelilah Benyoussef

THE EFFECT OF OFF-RAMP ON THE ONE-DIMENSIONAL CELLULAR AUTOMATON TRAFFIC FLOW WITH OPEN BOUNDARIES

The effect of the position of the off-ramp (way out), on the traffic flow phase transition is investigated using numerical simulations in the one-dimensional cellular automaton traffic flow model with open boundaries using parallel dynamics. When the off-ramp is located between two critical positions ic1 and ic2 the current increases with the extracting rate β0, for β0 β0c2. However, the density undergoes two successive first order transitions: from high density to plateau current phase at β0=β0c1; and from average density to the low one at β0=β0c2. In the case of two off-ramps located respectively at i1 and i2, these transitions occur only when i2-i1 is smaller than a critical value. Phase diagrams in the (α,β0), (β,β0) and (i1,β0) planes are established. It is found that the transitions between free traffic (FT), congested traffic (CT) and plateau current (PC) phases are of first order. The first order line tra...

Cellular automata model simulating traffic car accidents in the on-ramp system

In this paper, using Nagel–Schreckenberg model we study the on-ramp system under the expanded open boundary condition. The phase diagram of the two-lane on-ramp system is computed. It is found that the expanded left boundary insertion strategy enhances the flow in the on-ramp lane. Furthermore, we have studied the probability of the occurrence of car accidents. We distinguish two types of car accidents: the accident at the on-ramp site (Prc) and the rear-end accident in the main road (Pac). It is shown that car accidents at the on-ramp site are more likely to occur when traffic is free on road A. However, the rear-end accidents begin to occur above a critical injecting rate αc1. The influence of the on-ramp length (LB) and position (xC0) on the car accidents probabilities is studied. We found that large LB or xC0 causes an important decrease of the probability Prc. However, only large xC0 provokes an increase of the probability Pac. The effect of the stochastic randomization is also computed.

Velocity Correlations In The Nagel–Schreckenberg Model

The correlation between the velocity of two successive vehicles as a function of time headway is studied in the one-dimensional cellular automata (CA) NaSch model within parallel dynamic update. It is found that a strong correlation occurs in short time headway. The behavior of the correlation velocity as a function of the car density in different traffic states is also investigated. Moreover, our study is also extended to a more complicated situation where the two vehicles are separated by a number n of other vehicles. It is shown that the velocity correlation coefficient depends strongly on the number n of vehicles in between and on their positions.

Monte Carlo Simulations of Mixed Highly Frustrated Systems

We have performed Monte Carlo simulations on the mixed highly frustrated K2CuxMn1-xF4 and FexMn1-xTiO3 systems. Transitions of random systems with well-established universality classes are obtained. This study allows us to investigate mainly the usual and re-entrant spin glass and criticality associated with these states. The ratio x of substitution (or dilution) is found to have a large influence on the nature of this criticality.

TRAFFIC MODEL WITH QUENCHED DISORDER

Abstract Using numerical simulations, we study the effects of defects in the road and of jumping rate Δt on the phase diagram J - ϱ . For different level of disorder, the space-time evolution of particles displays “waves” for both low density and high density phases. Besides, there exist two critical values of density, a lower critical value ϱ c 1 and a upper critical value ϱ c 2 , in between the current is constant and reaches its maximal value J max which increases with increasing the jumping rate Δt and/or the degree of disorder c . The critical densities ϱ c 1 and ϱ c 2 depend on the values of Δt and c . Indeed, when increasing Δt and/or c , ϱ c 1 increases and ϱ c 2 decreases. The known results for the perfect road are also obtained.

Simulation study of car accidents at the intersection of two roads in the mixed traffic flow

Using cellular automata (CA) Nagel–Schreckenberg (NaSch) model, we numerically study the probability Pac of the occurrence of car accidents at nonsignalized intersection when drivers do not respect the priority rules. We also investigated the impact of mixture lengths and velocities of vehicles on this probability. It is found that in the first case, where vehicles distinguished only by their lengths, the car accidents start to occur above a critical density ρc. Furthermore, the increase of the fraction of long vehicles (FL) delays the occurrence of car accidents (increasing ρc) and increases the risk of collisions when ρ > ρc. In other side, the mixture of maximum velocities (with same length for all vehicles) leads to the appearance of accidents at the intersection even in the free flow regime. Moreover, the increase of the fraction of fast vehicles (Ff) reduces the accident probability (Pac). The influence of roads length is also studied. We found that the decrease of the roads length enhance the risk of collision.

Phase transitions in the anisotropic Ashkin–Teller model

By using mean-field approximation (MFA) and Monte-Carlo (MC) simulations, we have studied the effect of the anisotropy on the phase diagrams of the Ashkin–Teller model (A.T.M.) on a hypercubic lattice. By varying the strength of the anisotropic parameter, partially ordered phases, connected by symmetry, and denoted by 〈σ〉 and 〈S〉 appear in all dimensions d>1 as in the three dimensional isotropic case for antiferromagnetic interactions. The MC simulations reduce the varieties of phase diagrams obtained from MFA to one variety. In d=2 the phase diagrams present Ising-like phase transitions while in d=3 a first order phase transition and then multicritical points appear.

Cellular automata traffic flow behavior at the intersection of two roads

The control of vehicles in urban traffic is a requirement to maximize the flow and to ensure the safety of traffic. Using the cellular automata Nagel–Schreckenberg (NaSch) model within a parallel dynamic update, we studied the effect of the intersection of two symmetrical roads, with typical periodic boundary conditions. It is found that the fundamental diagram depends strongly on the probability P of priority and the probability P1 of changing the road at the intersection. Beside the free flow, the platoon and the jamming phases, the fundamental diagram exhibits a fourth new phase occurring for any value of P ≠ 0.5, which disappears gradually as one increases the probability P, and disappears completely for P = 0.5. The effects of the braking probability Pb on the fundamental diagram and space time structures are also computed for different values of maximal velocities.

An effective field study of the magnetic properties and critical behaviour at the surface Ising film

The influence of corrugation and disorder at the surface on the critical bahaviour of a ferromagnetic spin-1/2 Ising film is investigated using mean-field theory and finite cluster approximation. It is found that the critical surface exponent β1 follows closely the one of a perfect surface, in the two cases: corrugated surface and random equiprobable coupling surface. However, in the case of flat surface with random interactions the surface critical exponent β1 depends on the concentration p of the strong interaction for p>pc=0.5, while for p⩽pc, such critical exponent is independent of the value of p and is equal to the one of the perfect surface. Moreover, in the case of corrugated surface, the effective exponent for a layer z,βeff(z,n), is calculated as a function of the number of steps at the surface.

Simulation study of traffic car accidents at a single lane roundabout

In this paper, using the Nagel-Schreckenberg model, we numerically investigate the probability Pac of entering/circulating car accidents to occur at single-lane roundabout under the expanded open boundary. The roundabout consists of N on-ramps (respectively, off-ramps). The boundary is controlled by the injecting rates α1,α2 and the extracting rate β. The simulation results show that, depending on the injecting rates, the car accidents are more likely to happen when the capacity of the rotary is set to its maximum. Moreover, we found that the large values of rotary size L and the probability of preferential Pexit are reliable to improve safety and reduce accidents. However, the usage of indicator, the increase of β and/or N provokes an increase of car accident probability.