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Ludger Santen

Publications and source records attributed to Ludger Santen.

48 records · Page 3Linked to original sources
arXiv2002

Optimization potential of a real highway network: an empirical study

Empirical observations and theoretical studies indicate that the overall travel-time of vehicles in a traffic network can be optimized by means of ramp metering control systems. Here, we present an analysis of traffic data of the highway network of North-Rhine-Westfalia in order to identify and characterize the sections of the network which limit the performance, i.e., the bottlenecks. It is clarified whether the bottlenecks are of topological nature or if they are constituted by on-ramps. This allows to judge possible optimization mechanisms and reveals in which areas of the network they have to be applied.

cond-mat.stat-mech↗
arXiv2002

Single-vehicle data of highway traffic: microscopic description of traffic phases

We present a detailed analysis of single-vehicle data which sheds some light on the microscopic interaction of the vehicles. Besides the analysis of free flow and synchronized traffic the data sets especially provide information about wide jams which persist for a long time. The data have been collected at a location far away from ramps and in the absence of speed limits which allows a comparison with idealized traffic simulations. We also resolve some open questions concerning the time-headway distribution.

cond-mat.stat-mech↗
arXiv2001

Liquid, Glass and Crystal in Two-dimensional Hard disks

We study the thermodynamic and dynamic phase transitions in two-dimensional polydisperse hard disks using Monte Carlo methods. A conventional local Monte Carlo algorithm allows us to observe a dynamic liquid-glass transition at a density, which depends very little on the degree of polydispersity. We furthermore apply Monte Carlo methods which sample the Boltzmann equilibrium distribution at any value of the density and polydispersity, and remain ergodic even far within the glass. We find that the dynamical transition is not accompanied by a thermodynamic transition in this two-dimensional system so that the glass is thermodynamically identical to the liquid. Moreover, we scrutinize the polydispersity-driven transition from the crystal into the disordered phase (liquid or glass). Our results indicate the presence of a continuous (Kosterlitz-Thouless type) transition upon increase of the polydispersity.

cond-mat.stat-mech↗
arXiv2001

Human behavior as origin of traffic phases

It is shown that the desire for smooth and comfortable driving is directly responsible for the occurrence of complex spatio-temporal structures (``synchronized traffic'') in highway traffic. This desire goes beyond the avoidance of accidents which so far has been the main focus of microscopic modeling and which is mainly responsible for the other two phases observed empirically, free flow and wide moving jams. These features have been incorporated into a microscopic model based on stochastic cellular automata and the results of computer simulations are compared with empirical data. The simple structure of the model allows for very fast implementations of realistic networks. The level of agreement with the empirical findings opens new perspectives for reliable traffic forecasts.

cond-mat.stat-mech↗
arXiv2001

Boundary induced phase transitions in driven lattice gases with meta-stable states

We study boundary induced phase transitions in a driven lattice gas exhibiting metastability. The phase diagram for open systems, parameterized by the input and output rates, consists of two regions corresponding to the free flow and jammed phase. Both have been entirely characterized. The microscopic states in the high density phase are shown to have an interesting striped structure, which survives in the thermodynamic limit.

cond-mat.stat-mech↗
arXiv2000

Towards a realistic microscopic description of highway traffic

Simple cellular automata models are able to reproduce the basic properties of highway traffic. The comparison with empirical data for microscopic quantities requires a more detailed description of the elementary dynamics. Based on existing cellular automata models we propose an improved discrete model incorporating anticipation effects, reduced acceleration capabilities and an enhanced interaction horizon for braking. The modified model is able to reproduce the three phases (free-flow, synchronized, and stop-and-go) observed in real traffic. Furthermore we find a good agreement with detailed empirical single-vehicle data in all phases.

cond-mat.stat-mech↗
arXiv2000

Statistical Physics of Vehicular Traffic and Some Related Systems

In the so-called "microscopic" models of vehicular traffic, attention is paid explicitly to each individual vehicle each of which is represented by a "particle"; the nature of the "interactions" among these particles is determined by the way the vehicles influence each others' movement. Therefore, vehicular traffic, modeled as a system of interacting "particles" driven far from equilibrium, offers the possibility to study various fundamental aspects of truly nonequilibrium systems which are of current interest in statistical physics. Analytical as well as numerical techniques of statistical physics are being used to study these models to understand rich variety of physical phenomena exhibited by vehicular traffic. Some of these phenomena, observed in vehicular traffic under different circumstances, include transitions from one dynamical phase to another, criticality and self-organized criticality, metastability and hysteresis, phase-segregation, etc. In this critical review, written from the perspective of statistical physics, we explain the guiding principles behind all the main theoretical approaches. But we present detailed discussions on the results obtained mainly from the so-called "particle-hopping" models, particularly emphasizing those which have been formulated in recent years using the language of cellular automata.

cond-mat.stat-mech↗
arXiv2000

Absence of Thermodynamic Phase Transition in a Model Glass Former

The glass transition can simply be viewed as the point at which the viscosity of a structurally disordered liquid reaches 10^{13} Poise [1]. This definition is operational but it sidesteps fundamental controversies about the glass: Is the transition a purely dynamical phenomenon [2]? This would mean that ergodicity gets broken, but that thermodynamic properties of the liquid remain unchanged across the transition if determined as thermodynamic equilibrium averages over the whole phase space. The opposite view [3-6] claims that an underlying thermodynamic phase transition is responsible for the dramatic slowdown at the liquid-glass boundary. Such a phase transition (which shows up in proper equilibrium phase space averages) would trigger the dynamic standstill, and then get masked by it. A recent Monte Carlo algorithm [7] introduces non-local moves for hard-core systems in a way which preserves micro-reversibility. Here we use this method to equilibrate a two-dimensional hard disc system far within its glassy phase. We show that indications of a thermodynamic transition are lacking up to very high densities, and that the glass is indistinguishable from the liquid on purely thermodynamic grounds.

cond-mat.stat-mech↗
arXiv1999

Vehicular Traffic: A System of Interacting Particles Driven Far From Equilibrium

In recent years statistical physicists have developed {\it discrete} "particle-hopping" models of vehicular traffic, usually formulated in terms of {\it cellular automata}, which are similar to the microscopic models of interacting charged particles in the presence of an external electric field. Concepts and techniques of non-equilibrium statistical mechanics are being used to understand the nature of the steady states and fluctuations in these so-called "microscopic" models. In this brief review we explain, primarily to the nonexperts, these models and the physical implications of the results.

cond-mat.stat-mech↗
arXiv1999

Spatio-temporal organization of vehicles in a cellular automata model of traffic with 'slow-to-start' rule

The spatio-temporal organizations of vehicular traffic in cellular-automata models with "slow-to-start" rules are qualitatively different from those in the Nagel-Schreckenberg (NaSch) model of highway traffic. Here we study the effects of such a slow-to-start rule, introduced by Benjamin, Johnson and Hui (BJH), on the the distributions of the distance-headways, time-headways, jam sizes and sizes of the gaps between successive jams by a combination of approximate analytical calculations and extensive computer simulations. We compare these results for the BJH model with the corresponding results for the NaSch model and interpret the qualitative differences in the nature of the spatio-temporal organizations of traffic in these two models in terms of a phase separation of the traffic caused by the slow-to-start rule in the BJH model.

cond-mat.stat-mech↗
arXiv1998

Disorder effects in cellular automata for two-lane traffic

For single-lane traffic models it is well known that particle disorder leads to platoon formation at low densities. Here we discuss the effect of slow cars in two-lane systems. Surprisingly, even a small number of slow cars can initiate the formation of platoons at low densities. The robustness of this phenomenon is investigated for different variants of the lane-changing rules as well as for different variants on the single-lane dynamics. It is shown that anticipation of drivers reduces the influence of slow cars drastically.

cond-mat.stat-mech↗