Development of control strategy of variable speed limits for improving traffic operations at freeway bottlenecks

A control strategy of variable speed limits(VSL)was developed to reduce the travel time at freeway recurrent bottleneck areas.The proposed control strategy particularly focused on preventing the capacity drop and increasing the discharge flow.A cell transmission model(CTM)was developed to evaluate the effects of the proposed VSL control strategy on the traffic operations.The results show that the total travel time is reduced by 25.5% and the delay is reduced by 56.1%.The average travel speed is increased by 34.3% and the queue length is reduced by 31.0%.The traffic operation is improved by the proposed VSL control strategy.The way to use the proposed VSL control strategy in different types of freeway bottlenecks was also discussed by considering different traffic flow characteristics.It is concluded that the VSL control strategy is effective for merge bottlenecks but is less effective for diverge bottlenecks.

Differential variable speed limits to improve performance and safety of car-truck mixed traffic on freeways

This study develops a differential variable speed limit(DVSL)which assigns different speed limits for car and truck,and varies speed limits based on traffic conditions.The proposed DVSL algorithm changes speed limits in real time based on truck percentage and occupancy immediately upstream of the ramp and the average speed of the control road sections upstream of the ramp.DVSL algorithm also considers spatial coordination of speeds,which gradually changes the speed limits in successive road sections upstream of the ramp when the severe congestion occurs.The study tested the impacts of DVSL and three other speed limit strategies on delay and safety for a section of the Gardiner Expressway in Toronto,Canada using the VISSIM traffic simulation model.The other strategies are 1)uniform speed limit(USL),2)differential speed limit for car and truck(DSL),and 3)USL&DSL(U&D)-i.e.,USL at low truck percentage and DSL at high truck percentage.It was found that DVSL showed the lowest delays for both car and truck among the four strategies.This is mainly because DVSL increased the spacing between vehicles in the right lane upstream of the on-ramp and facilitated vehicles’merging into the mainline freeway.It was also found that DVSL showed the lowest likelihood of rear-end crash between the lead and following vehicles among the four strategies.This study demonstrates that the proposed DVSL algorithm can better control car and truck speeds to reduce delay and improve safety of car-truck mixed traffic flow on freeways.

Technology acceptance comparison between on-road dynamic message sign and on-board human machine interface for connected vehicle-based variable speed limit in fog area

Purpose–Connected vehicle-based variable speed limit(CV-VSL)systems in fog area use multi-source detection data to indicate drivers to make uniform change in speed when low visibility conditions suddenly occur.The purpose of the speed limit is to make the driver’s driving behavior more consistent,so as to improve traffic safety and relieve traffic congestion.The on-road dynamic message sign(DMS)and on-board human–machine interface(HMI)are two types of warning technologies for CV-VSL systems.This study aims to analyze drivers’acceptance of the two types of warning technologies in fog area and its influencing factors.Design/methodology/approach–This study developed DMS and on-board HMI for the CV-VSL system in fog area on a driving simulator.The DMS and on-board HMI provided the driver with weather and speed limit information.In all,38 participants participated in the experiment and completed questionnaires on drivers’basic information,perceived usefulness and ease of use of the CV-VSL systems.Technology acceptance model(TAM)was developed to evaluate the drivers’acceptance of CV-VSL systems.A variance analysis method was used to study the influencing factors of drivers’acceptance including drivers’characteristics,technology types and fog density.Findings–The results showed that drivers’acceptance of on-road DMS was significantly higher than that of on-board HMI.The fog density had no significant effect on drivers’acceptance of on-road DMS or on-board HMI.Drivers’gender,age,driving year and driving personality were associated with the acceptance of the two CV-VSL technologies differently.This study is beneficial to the functional improvement of on-road DMS,on-board HMI and their market prospects.Originality/value–Previous studies have been conducted to evaluate the effectiveness of CV-VSL systems.However,there were rare studies focused on the drivers’attitude toward using which was also called as acceptance of the CV-VSL systems.Therefore,this research calculated the drivers’acceptance of two normally used CV-VSL systems including on-road DMS and on-board HMI using TAM.Furthermore,variance analysis was conducted to explore whether the factors such as drivers’characteristics(gender,age,driving year and driving personality),technology types and fog density affected the drivers’acceptance of the CV-VSL systems.

Exploring the impact of a coordinated variable speed limit control on congestion distribution in freeway

Over the past few decades, urban freeway congestion has been highly recognized as a serious and worsening traffic problem in the world. To relieve freeway congestion, several active traffic and demand management （ATDM） methods have been developed. Among them, variable speed limit （VSL） aims at regulating freeway mainline flow upstream to meet existing capacity and to harmonize vehicle speed. However, congestion may still be inevitable even with VSL implemented due to extremely high demand in actual practice. This study modified an existing VSL strategy by adding a new local constraint to suggest an achievable speed limit during the control period. As a queue is a product of the congestion phenomenon in freeway, the incentives of a queue build-up in the applied coordinated VSL control situation were analyzed. Considering a congestion occurrence （a queue build-up） characterized by a sudden and sharp speed drop, speed contours were utilized to demonstrate the congestion distribution over a whole freeway network in various sce- narios. Finally, congestion distributions found in both VSL control and non-VS control situations for various scenarios were investigated to explore the impact of the applied coordinated VSL control on the congestion distribution. An authentic stretch of V^hitemud Drive （I~~ID）, an urban freeway corridor in Edmonton, Alberta, Canada, was employed to implement this modified coordinated VSL control strategy; and a calibrated micro-simu- lation VISSIM model （model functions） was applied as the substitute of the real-world traffic system to test the above mentioned performance. The exploration task in this study can lay the groundwork for future research on how to improve the presented VSL control strategy for achieving the congestion mitigation effect on freeway.

Predictive Control Model Based on the MPC Algorithm on Three Different Road Sections

Predictive control is an advanced control algorithm,which is widely used in industrial process control.Among them,model predictive control(MPC)is an important branch of predictive control.Its basic principle is to use the system model to predict future behavior and determine the current control action by optimizing the objective function.This paper discusses the application of MPC in the prediction and control of the speed of vehicles to optimize traffic flow.It is a valuable reference for alleviating traffic congestion and improving travel efficiency and smoothness and provides scientific basis and technical support for future highway traffic management.

Smart Dynamic Trafc Monitoring and Enforcement Syste

Enforcement of trafc rules and regulations involves a wide range of complex tasks,many of which demand the use of modern technologies.variable speed limits(VSL)control is to change the current speed limit according to the current trafc situation based on the observed trafc conditions.The aim of this study is to provide a simulation-based methodological framework to evaluate(VSL)as an effective Intelligent Transportation System(ITS)enforcement system.The focus of the study is on measuring the effectiveness of the dynamic trafc control strategy on trafc performance and safety considering various performance indicators such as total travel time,average delay,and average number of stops.United Arab Emirates(UAE)was selected as a case study to evaluate the effectiveness of this strategy.A micro simulation software package VISSIM with add-on module VisVAP is used to evaluate the impacts of VSL.It has been observed that VSL control strategy reduced the average delay time per vehicle to around 7%,travel time by 3.2%,and number of stops by 48.5%.Dynamic trafc control strategies also alleviated congestion by increasing the capacity of the bottleneck section and improving safety.Results of this study would act as a guidance for engineers and decision makers to new trafc control system implementation.

Analysis of highway performance under mixed connected and regular vehicle environment

Purpose–This study aims to study the connected vehicle(CV)impact on highway operational performance under a mixed CV and regular vehicle(RV)environment.Design/methodology/approach–The authors implemented a mixed trafficflow model,along with a CV speed control model,in the simulation environment.According to the different traffic characteristics between CVs and RVs,this researchfirst analyzed how the operation of CVs can affect highway capacity under both one-lane and multi-lane cases.A hypothesis was then made that there shall exist a critical CV penetration rate that can significantly show the benefit of CV to the overall traffic.To prove this concept,this study simulated the mixed traffic pattern under various conditions.Findings–The results of this research revealed that performing optimal speed control to CVs will concurrently benefit RVs by improving highway capacity.Furthermore,a critical CV penetration rate should exist at a specified traffic demand level,which can significantly reduce the speed difference between RVs and CVs.The results offer effective insight to understand the potential impacts of different CV penetration rates on highway operation performance.Originality/value–This approach assumes that there shall exist a critical CV penetration rate that can maximize the benefits of CV implementations.CV penetration rate(the proportion of CVs in mixed traffic)is the key factor affecting the impacts of CV on freeway operational performance.The evaluation criteria for freeway operational performance are using average travel time under different given traffic demand patterns.

Integrated control of highway traffic flow

Several efforts have been made during recent years on the control of traffic flow using ramp metering,variable speed limit and lane change control.Most of these techniques reported significant traffic mobility improvements in macroscopic simulations,which cannot be confirmed in some microscopic simulation cases.We demonstrate that the lack of travel time improvement is due to the forced lane changes at the bottleneck which introduce a capacity drop.In this paper,a lane change controller is proposed which provides lane change recommendations to avoid the capacity drop.Combined with the lane change control,a feedback linearisation variable speed limit controller which maintains the bottleneck flow at the maximum level and coordinates with ramp metering controllers is proposed.The integrated VSL,RM and LC controller can improve system performance,manage the ramp queues and maintain the fairness between mainline and on-ramp flows.Microscopic simulations show consistent improvements under different scenarios.