Akira Kawamura

Experimental analysis of car-following dynamics and traffic stability

The study of car-following dynamics is useful for capacity analysis, safety research, and traffic simulation. There is also growing interest in its applications in intelligent transportation systems, such as advanced vehicle control and safety systems and autonomous cruise control systems. A large number of car-following models have been developed in the past five decades. Some of them were investigated and validated against experimental data; nevertheless, the results were not that con sistent for some models, e.g., those for the General Motors (GM) model. As a part of the problem, the data acquisition and calibration techniques were not advanced then. The past few decades have seen remark able advancements in these techniques, e.g., the use of the differential Global Positioning System (GPS) for position measurement, the use of Dopplers principle for speed measurements, and the use of genetic algorithms for optimization. It might be useful to reassess some out standing issues in car-following dynamics ...

Online Estimation of Friction Coefficients of Winter Road Surfaces Using the Unscented Kalman Filter

An innovation to a previously proposed method for estimating friction coefficients of winter road surfaces was achieved through the introduction of a relatively new algorithm, the unscented Kalman filter. Its use, instead of a generic algorithm, made estimating friction coefficients in real time possible while keeping the core vehicular motion model unchanged. The problem of estimating such coefficients was too complicated to apply conventional feedback techniques, such as an extended Kalman filter, because of the presence of not only a nonlinear algebra equation but also a set of multiple differential equations. The unscented Kalman filter did not require any explicit function of state and observation equations in deriving Kalman gain. This paper describes the usefulness of this new filter in solving the problem and describes numerical experiments that validated the effectiveness of the proposed new method in terms of computational efficiencies. The friction coefficients estimated with the new technique were in fairly good accordance with those measured in the field.

Lifting Scheme Theory to Detect Road Surface Waveform Influencing Vehicle Vibration

Vehicle vibration is caused by road roughness. When wavelength and amplitude are at the same level and the road surface waveform is different, the vibration waveform can also be different. When vehicle-road interaction is strictly analyzed, it is necessary to divide the vehicle vibration data according to the type of road surface waveform. The lifting scheme theory, which is based on the wavelet transform, was used to consider the road surface waveform detection method, which is influenced by the unsprung mass vibration of a vehicle. The basis function used optimizes the shape corresponding to the analysis purpose, based on the spline function. This method can accurately monitor the unsprung mass vibration of a convex type waveform of high magnitude.

Inverse Estimation of Friction Coefficients of Winter Road Surfaces: New Considerations of Lateral Movements and Angular Movements

This study is an extension of a method developed in a previous paper. The major concern remains one of how to estimate the friction coefficient of a winter road surface indirectly with the use of vehicular motion data. Similarly, in this paper, there is no change in the central structure of the argument; the friction coefficient is estimated as the solution to an optimization problem in which a tire model describing the interaction between tire and road surface is integrated into a genetic algorithm. The tire model differs from the previous method. The one-degree-of-freedom (1-DOF) model that formulated only longitudinal motion is replaced by a 3-DOF model, in which lateral and angular motions have also been taken into account. This revised method was applied to data measured at three sites: at intersections on a test track, on curved sections of the same test track, and at intersections on arterials in Sapporo, Japan. The friction coefficients estimated by the method were in relatively good agreement with those actually measured. Lateral and angular motions have contributed to the improvement.

Transformation between uninterrupted and interrupted speeds for urban road applications

Unlike the freeway traffic stream, the urban traffic stream is generally interrupted by signals, and the traffic data observed may differ from the true (uninterrupted) flow characteristics. This paper deals with the transformation between interrupted and uninterrupted speeds on an urban road with signalized intersections. The conventional shock wave model and two modified versions of the shock wave boundary that address unrealistic characteristics of the conventional shock wave model are developed. A method of integrating probe and detector data for speed transformation is also discussed. The proposed methods are tested with a virtual isolated signalized intersection by varying the approach demand. The numerical results suggest that all models can significantly reduce the difference between the actual and the estimated uninterrupted (or interrupted) speeds compared with the case of doing nothing. The applications of the proposed methods, including the development of a flow-speed model and link travel time...

Airport pavement roughness evaluation based on aircraft response

Runway roughness affects primarily ride quality and dynamic wheel loads. The forces applied onto the airport pavement by aircraft vary instantaneously above and blow the static weight, which in turn increase the runway roughness. One method to effectively assess the ride quality of the airport runway is to measure its longitudinal profile and numerical simulate aircraft response performing a takeoff, landing or taxiing on that profile data. In this study the aircraft responses excited as the aircraft accelerates or moves at a constant speed on the runway during takeoff and taxi are computed by using the improved computer program TAXI. This procedure is capable of taking into account both the effects of discrete runway bumps and runway roughness. Thus, sections of significant dynamic response can be determined, and the maintenance and rehabilitation works for airport runways will be conducted.

TAKING TIRE SLIP RATIO INTO ACCOUNT AND ESTIMATING FRICTION COEFFICIENTS IN REAR-END COLLISIONS ON WINTER ROADS

Road surface conditions in winter are very transient. A small change in the friction coefficient can have a large effect on vehicular movements. A friction coefficient measured at the scene directly after an accident may be different from the one at the time when the accident occurred. A traffic accident reconstruction method that can estimate friction coefficients based indirectly on in situ data is presented. First, it is pointed out that the friction coefficient is largely dependent on the tire slip ratio, in particular that of studless tires whose tread rubber is very soft and adhesive. It is emphasized that it makes sense to use a tire model that considers the slip ratio to estimate the friction coefficients more precisely. Rear-end collision accident data were collected. The types of vehicles involved in accidents were identified, and their friction coefficients at the time of skidding were estimated by the new reconstruction model. The friction coefficients estimated by this model were compared with those estimated by a conventional rigid-body model. In addition, by inversely calculating the friction coefficient required to avoid accidents, how an increment in the friction coefficient could greatly improve traffic safety is considered. Finally, it is shown that a threshold defined as the intersection of the cumulative curves of both friction coefficients provides useful information for winter maintenance.