Driver’s Critical Gap Calibration at Urban Roundabouts: A Case Study in China

Roundabouts have been used successfully in cities throughout the world and are wildly used in China, The critical gap is a required parameter for calculating the capacity of roundabouts and deciding the needs for stop signs, While many studies on gap acceptance characteristics at roundabouts have been carried out in America and Europe, few have been done in China, This study was conducted to calibrate the critical gap in a roundabout in China, The differences between critical gaps on different days （workdays and weekends） and during different times （rush hour and non rush hour） were checked. The study was performed at a three-lane roundabout formed by a two-way and four-lane local road and a six-lane divided artery. The data was collected at this site by a video camera. The evaluations included the cumulative probability distributions of the acceptable and rejected gaps which resulted in critical gaps for all cases. The results show that the critical gap during the rush hour is shorter than after the rush hour, but the difference is not large and the cumulative probability distributions can be fit by the logit functional form with parameters estimated using linear regression.

Analyzing variations in spatial critical gaps at two-way stop controlled intersections using parametric and non-parametric techniques

At two-way stop controlled(TWSC)intersections drivers on minor stream are generally at risk because of the difficulty in judging safe gap between major stream vehicles.Any misjudgment by the driver while choosing gap may result in a collision with major stream vehicle.This paper provides important insights for determining and analyzing spatial critical gaps of drivers at high speed and medium speed TWSC intersections.The critical gap line(CGL)fitted for the accepted and rejected gaps using parametric(binary logit model-BLM)and non-parametric(support vector machines-SVM)techniques gives critical gap values at 15 th,50 th and 85 th percentile speeds.The evaluation of spatial critical gap with respect to major road vehicle(conflicting vehicle)speed makes it easier to understand the impact of variation in speed on spatial gaps accepted by the drivers on the minor road.The logit models developed revealed that the probability of accepting gap decreases with increase in the speed of the conflicting vehicle and it increases with increase in the distance of conflicting vehicle.The spatial critical gaps estimated using support vector machines were found in close approximation with those estimated using binary logit model.The study results showed that SVMs have very good potential to be an alternative tool for the estimation of driver's critical gap.The spatial critical gaps corresponding to 15 th,50 th and 85 th percentile speeds for medium speed intersections were 32 m,38 m and 46 m respectively and for high speed intersections these values were 64 m,76 m and 104 m respectively.The increase in the magnitude of gap value with respect to the percentile speed clearly states the effect of speed on spatial gaps.The insights from the study can be used to suggest various measures to improve the safety of crossing drivers at uncontrolled intersections.

Critical Behavior of the Energy Gap and Its Relation with the Berry Phase Close to the Excited State Quantum Phase Transition in the Lipkin Model

In our previous work [Phys. Rev. A 85 （2012） 044102], we studied the Berry phase of the ground state and exited states in the Lipkin model. In this work, using the Hellmann-Feynman theorem, we derive the relation between the energy gap and the Berry phase closed to the excited state quantum phase transition （ESQPT） in the Lipkin model. It is found that the energy gap is approximately linearly dependent on the Berry phase being closed to the ESQPT for large N. As a result, the critical behavior of the energy gap is similar to that of the Berry phase. In addition, we also perform a semiclassical qualitative analysis about the critical behavior of the energy gap.

Study on the model of pedestrian cross-time in signalized intersection

For studying the law of pedestrian cross-time in the signalized intersection, based on gap theory, a probability chorological discipline model of crossing pedestrians is built based on the observed data. Moreover, the number of pedestrians passing through in a critical gap is estimated under different conditions by three models. Then the models of pedestrian crosswalk average time, the 85th percentile pedestrian cross-time and the 90th percentile pedestrian cross-time are deduced. By quantitative analyses and the exemplification of the models, the main correlative factors acting on pedestrian cross-time are found, including the length of the crosswalk, the probability of the time-headway being less than the critical gap and the number of the turned motor vehicles in the intersection. The results indicate that the estimated errors of the models are less than 5%.

Control strategy for multiple capsule robots in intestine

Based on the critical gap phenomenon of the intestinal capsule robot,a variable-diameter capsule robot with radial gap self-compensation is developed in this paper.With the functional variation principle,a fluid dynamic pressure model satisfying the boundary conditions of the outer surface of capsule robot with screw blades is derived.The critical gap phenomenon is studied theoretically and experimentally based on the end effect and the dynamic balance characteristics of the fluid on the surface of capsule robot.The concept of start-up rotation speed is defined,the relationship between the start-up rotation speed and the spiral parameters of capsule robot is investigated.The strategy for implementing drive and control on several capsule robots under the same rotational magnetic field is proposed,and by defining the start-up curves of several capsule robots with the similar motion regulation as the objective functions,genetic algorithm is employed to optimize the spiral parameters of several capsule robots.Experiments have shown that the proposed drive and control strategy for several capsule robots can be implemented effectively.It has a good prospect of application inside intestine to realize the drive and control on several capsule robots for different medical purposes.

Modelling follow up time at a single-lane roundabout

The follow up time is an important parameter for estimating the entry capacity of roundabouts. However, its variability and contributing factors have long been ignored in the literatures. In this study, 171 follow up samples and contributing factors （traffic volume, vehicle position, waiting vehicles behind, vehicle type, and drivers＇ gender） are collected at a roundabout in Pacific Pines, Australia. It is found that the follow up time is indeed significantly affected by traffic volume, waiting vehicles behind, vehicle type, and drivers＇ gender. In order to establish the relationship between the follow up time and its contributing factors, an inverse Gaussian regression model is further developed. This relationship could be applied to estimate the entry capacities by taking into account the variability of follow up samples. According to the model, the traffic volume and vehicle types are the most important contributing factors.

Analysis of motorcycle microscopic characteristics at roundabouts under mixed traffic condition:A case study of Vietnam

Recently,the demand for comprehension of mixed traffic in developing countries,particularly at roundabouts,which are highly interactive road junctions,has increased.Thus,we analyzed mixed traffic at roundabouts,considering Vietnam as a case study.The two main objectives of this study were to characterize the mixed traffic in Vietnam and to determine the microscopic characteristics of motorcycles at roundabouts.First,efforts were made to clarify the two constitutions of mixed traffic(the performance rule and the presence of small-sized vehicles),and the term“motorcycle-oriented mixed traffic”was defined.Even when satisfying the two fundamental constitutions,this traffic state has unique features,e.g.,only one type of non-lane-based vehicle(the motorcycle)and the predominance of motorcycles in the traffic composition(91.7%).Second,four microscopic characteristics of motorcycles were obtained from a large dataset:the motorcycles’continuous changes in speed,the relationship between the turning angle rate and the speed,the critical gap,and the following space.The relationship between the turning angle rate and the speed was first formulated as a power curve.The critical gap of motorcycles was estimated as a small value(1.25 s)in the case study.The following spaces varied with respect to the speed and had an oval shape.The smallest lateral and longitudinal dimensions were 1.5 and 1.74 m,respectively.While all the findings are meaningful,they are restricted to the case study(Ho Chi Minh City,Vietnam).

Dynamical mass generation in QED_3 beyond the instantaneous approximation

In this paper, we investigate dynamical mass generation in（2＋1）-dimensional quantum electrodynamics at finite temperature. Many studies are carried out within the instantaneous-exchange approximation, which ignores all but the zero-frequency component of the boson propagator and fermion self-energy function. We extend these studies by taking the retardation effects into consideration. In this paper, we get the explicit frequency n and momentum p dependence of the fermion self-energy function and identify the critical temperature for different fermion flavors in the chiral limit. Also, the phase diagram for spontaneous symmetry breaking in the theory is presented in Tc-Nf space. The results show that the chiral condensate is just one-tenth of the scale of previous results, and the chiral symmetry is restored at a smaller critical temperature.