Shin-ichi Tadaki

Coupled Map Traffic Flow Simulator Based on Optimal Velocity Functions

A coupled map traffic flow model is introduced, based on optimal velocity functions. The model is simulated under open boundary conditions. Effects of noises in velocity are investigated. The average car density increases with the noise level. The high throughput flow is realized when the noise level is sufficiently large, and power law behavior appears in temporal spectra of density fluctuations at the same time. By introducing traffic bottlenecks, a hysteresis loop, which indicates the emergence of traffic jams, is observed in the headway-velocity plane. Temporal spectra of density fluctuations also obey a power law in this case, whose exponent is independent of the noise level.

Metastability in the formation of an experimental traffic jam

We show detailed data about the process of jam formation in a traffic experiment on a circuit without any bottlenecks. The experiment was carried out using a circular road on a flat ground. At the initial stage, vehicles are running homogeneously distributed on the circuit with the same velocity, but roughly 10 min later a traffic jam emerges spontaneously on the circuit. In the process of the jam formation, we found a homogeneous flow with large velocity is temporarily realized before a jam cluster appears. The instability of such a homogeneous flow is the key to understanding jam formation.

Phase transition in traffic jam experiment on a circuit

The emergence of a traffic jam is considered to be a dynamical phase transition in a physics point of view; traffic flow becomes unstable and changes phase into a traffic jam when the car density exceeds a critical value. In order to verify this view, we have been performing a series of circuit experiments. In our previous work (2008 New J. Phys. 10 033001), we demonstrated that a traffic jam emerges even in the absence of bottlenecks at a certain high density. In this study, we performed a larger indoor circuit experiment in the Nagoya Dome in which the positions of cars were observed using a high-resolution laser scanner. Over a series of sessions at various values of density, we found that jammed flow occurred at high densities, whereas free flow was conserved at low densities. We also found indications of metastability at an intermediate density. The critical density is estimated by analyzing the fluctuations in speed and the density–flow relation. The value of this critical density is consistent with that observed on real expressways. This experiment provides strong support for physical interpretations of the emergence of traffic jams as a dynamical phase transition.

Self-Organization in a Two-Dimensional Cellular Automaton Model of Traffic Flow

The jam phases in a two-dimensional cellular automaton model of traffic flow are investigated by computer simulations. Two different types of jam phases are discussed. The low-density jam configurations show fractality and self-organization. The high-density jam configurations show randomness.

Noise Induced Congested Traffic Flow in Coupled Map Optimal Velocity Model

The optimal velocity traffic flow model is one of the car-following models which describe the behavior of cars by differential equations. In that model, each car controls its speed toward an optimal (safety) velocity, which depends only on the headway. We constructed a new car-following type simulation model for traffic flow in a coupled map form based on the optimal velocity model. We can easily simulate open road systems with the model. The emergence of weakly congested flow induced by noise is investigated. We observe the enhancement of the car density induced by noise. The strong traffic jam hardly occurs in open road systems. We discuss the problems of unrealistic acceleration in the optimal velocity model and the possibility of spontaneous formation of strong traffic jams.

Power-Law Fluctuation in Expressway Traffic Flow: Detrended Fluctuation Analysis

The temporal behavior of expressway traffic flow is a complex mixture of various time scales. The fundamental response time of drivers is on the order of 1 s, and the periodic appearances of traffi...

Analysis of congested flow at the upper stream of a tunnel

We analyze the traffic data observed at the upper stream of a tunnel (Nihonzaka Tunnel) on Tomei Expressway linking Nagoya with Tokyo. We observe the fundamental properties of the traffic flow including temporal sequences and statistical properties. We also observe the reverse-lane usage in which the flow on the fast lane exceeds the one on the slow lane.

Observation of Congested Two-lane Traffic Caused by a Tunnel

We observe the congested traffic flow in Tomei Expressway, a Japanese expressway linking Tokyo with Nagoya. Congestion occurs at the upper stream of a traffic blockade, Nihonzaka tunnel, in contrast to preceding observations at the upper stream of an on-ramp. The flow on the fast lane is congested more severely than on the slow lane. The flow on the fast lane, however, almost always exceeds the one on the slow lane. The observed congested flow is stable and the average velocity on both lanes strongly correlated.

Long-Term Power-Law Fluctuation in Internet Traffic

Power-law fluctuation in observed Internet packet flow are discussed. The data is obtained by a multi router traffic grapher (MRTG) system for 9 months. The internet packet flow is analyzed using the detrended fluctuation analysis. By extracting the average daily trend, the data shows clear power-law fluctuations. The exponents of the fluctuation for the incoming and outgoing flow are almost unity. Internet traffic can be understood as a daily periodic flow with power-law fluctuations.

Distribution of jam clusters in a two-dimensional cellular automaton traffic flow model with open boundaries

The distribution of jam clusters in a two-dimensional cellular automaton model of traffic flow with open boundaries is investigated by computer simulation. The size distribution of jam clusters obeys the power law of the injection rate in the high-injection-rate region. The total number of unmoved cars in jam clusters shows a sharp transition at the critical injection rate and can be an adequate order parameter describing the phase transition with the emergence of a traffic jam.