Impact of countdown signals on traffic safety and efficiency:a review and proposal

Countdown signals for motorized vehicles,which are intended to ensure safety on the road and regulate motor vehicle speed limits at road intersections,are still considered a relatively novel concept.These signals have been adopted by only a few countries,and the number of cities that use them is limited.This review aims to summarize the effects of countdown signals on traffic safety and efficiency and to determine the consistency and differences of existing research propositions on the matter.Based on the review,considerable research presents evidently different conclusions in the areas of driver red-light running and traffic safety.Particularly,some studies propose that countdown signals reinforce traffic safety,whereas others consider that such signals adversely affect traffic safety.Meanwhile,related literature provides varying conclusions on the aspect of traffic efficiency for vehicle headway.At present,the number of studies conducted regarding the driving behaviors of motorists toward countdown-signalized intersections is insufficient.Accordingly,such inadequate diversity in research causes difficulty in completely assessing the benefits and disadvantages of countdown signals.In this paper,an important future research direction on microcosmic driving psychological and physiological data combined with macro-driving behavior is proposed.

Speed Profile as a Tool to Estimate Traffic Calming Measures Efficiency

TCMs （traffic calming measures） are commonly installed in order to reduce speeds and volumes of traffic to acceptable levels and, thus, improve traffic safety as well as environmental impact when designed appropriately as a corridor or aerial implementation with proper spacing. Hence in many previous studies, their impact was mainly evaluated in scope of average and 85th percentile speed reduction. This paper presents and appraises the efficiency of calming measures of various types used in the city of Bialystok, Poland in terms of their influence zone. The assessment is based on speed profiles derived from individual test rides conducted with test vehicle equipped with GPS （global positioning system） data logger to obtain vehicle trajectory data. Speed measurements were conducted in vicinity of most commonly installed calming measures such as speed cameras, raised pedestrian crossing, raised intersection, speed bumps and speed cushion. The results reveal great differences within analysed devices and the usefulness of speed profiles in evaluation of their effectiveness. Speed bumps, most frequently used device in practice due to their low cost installation and speed reduction effectiveness, demonstrate lowest usefulness when influence zone is considered.

Effects of real-time traffic information systems on traffic performance under different network structures

The effects of real-time traffic information system(RTTIS)on traffic performance under parallel,grid and ring networks were investigated.The simulation results show that the effects of the proportion of RTTIS usage depend on the road network structures.For traffic on a parallel network,the performance of groups with and without RTTIS level is improved when the proportion of vehicles using RTTIS is greater than 0 and less than 30%,and a proportion of RTTIS usage higher than 90%would actually deteriorate the performance.For both grid and ring networks,a higher proportion of RTTIS usage always improves the performance of groups with and without RTTIS.For all three network structures,vehicles without RTTIS benefit from some proportion of RTTIS usage in a system.

A Situation-Aware Collision Avoidance Strategy for Car-Following

Abstract--In this paper, we discuss how to develop an appropriate collision avoidance strategy for car-following. This strategy aims to keep a good balance between traffic safety and efficiency while also taking into consideration the unavoidable uncertainty of position/speed perception/measurement of vehicles and other drivers. Both theoretical analysis and numerical testing results are provided to show the effectiveness of the proposed strategy. Index Terms--Collision avoidance, safety, traffic efficiency, uncertainty.

Multi-level objective control of AVs at a saturated signalized intersection with multi-agent deep reinforcement learning approach

Reinforcement learning(RL)can free automated vehicles(AVs)from the car-following constraints and provide more possible explorations for mixed behavior.This study uses deep RL as AVs’longitudinal control and designs a multi-level objectives framework for AVs’trajectory decision-making based on multi-agent DRL.The saturated signalized intersection is taken as the research object to seek the upper limit of traffic efficiency and realize the specific target control.The simulation results demonstrate the convergence of the proposed framework in complex scenarios.When prioritizing throughputs as the primary objective and emissions as the secondary objective,both indicators exhibit a linear growth pattern with increasing market penetration rate(MPR).Compared with MPR is 0%,the throughputs can be increased by 69.2%when MPR is 100%.Compared with linear adaptive cruise control(LACC)under the same MPR,the emissions can also be reduced by up to 78.8%.Under the control of the fixed throughputs,compared with LACC,the emission benefits grow nearly linearly as MPR increases,it can reach 79.4%at 80%MPR.This study employs experimental results to analyze the behavioral changes of mixed flow and the mechanism of mixed autonomy to improve traffic efficiency.The proposed method is flexible and serves as a valuable tool for exploring and studying the behavior of mixed flow behavior and the patterns of mixed autonomy.

Integrated Spacing Policy Considering Micro- and Macroscopic Characteristics

An appropriate spacing policy improves traffic flow and traffic efficiency while reducing commuting time and energy con-sumption.In this paper,the integrated spacing policy that combines the benefits of the constant time headway(CTH)and safety distance(SD)spacing policies is proposed in an attempt to improve traffic flow and efficiency.Firstly,the performance of the CTH and SD spacing policies is analyzed from the perspective of the microscopic characteristics of human-vehicle and the macroscopic characteristics of traffic flow.The switching law between CTH and SD spacing policies and the integrated spacing policy are then proposed to increase traffic efficiency according to the traffic conditions,and the critical speed for the proposed integrated spacing policy is derived.Using the proposed switching law,the integrated spacing policy utilizes the safety redundancy difference between the CTH and SD spacing policies in a flexible manner.Simulation tests demon-strate that the proposed integrated spacing policy increases traffic flow and that the traffic flow maintains string stability in a wider range of traffic flow density.