Variable Speed Limit System Research Articles

An Enhanced Motorway Control System for Mixed Manual/Automated Traffic Flow

Recent advances in vehicle automation technologies have opened up new perspectives for motorway traffic condition monitoring and macroscopic controls. When sufficient automated vehicles (AVs) are present, they can provide wide-ranging and spatiotemporally detailed traffic information. Furthermore, AVs can be programmed to comply with traffic laws and optimized to smooth traffic flows. Thus, deploying AVs are expected to address the issues encountered by the existing variable speed limit (VSL) systems. However, the appealing scenario that 90% or more AVs are on motorways is seen as a long-term goal. Therefore, this article explores the utilization of AV technologies in VSL systems under mixed traffic conditions where AVs coexist with manually driven vehicles. In this article, a VSL system using AVs as a source of data is presented. More specifically, an extended Kalman filter-based data assimilation method is proposed to estimate system variables (i.e., density, speed, critical density, and compliance rate) from the collected AV data. Following this, a model predictive control scheme is adopted to solve the optimal AV-data-based VSL control problem on the basis of estimated system variables. Finally, the efficiency of the proposed system is verified against a real motorway section in New Zealand.

Combined Ramp-Metering and Variable Speed Limit System for Capacity Drop Control at Merge Bottlenecks

AbstractThis paper proposes a ramp metering and variable speed limit (RM-VSL) control strategy to prevent and recover from capacity drop at freeway merge bottlenecks. Using bounded acceleration kin...

Full Bayesian Before-After Analysis of Safety Effects of Variable Speed Limit System

Variable speed limits (VSL) is a major Intelligent Transportation System (ITS) technology for controlling freeway mainline traffic, which have been increasingly used to improve traffic safety and operations efficiency of freeway traffic management. The primary objective of this study is to evaluate the safety impacts of the VSL system implemented on Interstate 5 in Seattle, United States since 2010. A Full Bayesian (FB) before-after analysis was conducted based on 9,787 crashes that occurred in a 72-month study period. The analysis was conducted for all crashes, crash severity levels, crash types, and crash causes. The FB before-after results implied that the total crash count was reduced by 32.23% with a standard deviation of 3.58% after the VSL system was applied on the freeway. The count of crashes with no injury decreased more than crashes with severe injury and possible injury. The effect of rear-end crash reduction was the most beneficial among all crash types, while the effect on sideswipe crash reduction was the least. The study also compared the traffic speed features in the before and after periods to fully evaluate the impacts of the VSL system on traffic operations. The result indicated that, with VSL control, the difference in speed was reduced by the VSL system. The results of this study are particularly valuable for policy and control strategy development, and cost-benefit evaluation associated with VSL system implementations.

Simulation-based Evaluation of Using Variable Speed Limit in Traffic Incidents

Abstract Variable Speed Limit (VSL) systems are used to improve the traffic conditions on road by adjusting the speed limits according to current traffic situations. The variable speed limit system usually comprises of stationary detectors to estimate the traffic condition and dynamic variable message signs at predefined locations for the application of new speed limits. In connected environment, the system can recognize bottlenecks due to the incident and, further, it is possible to use direct control of the connected vehicles to adjust vehicle speeds towards the new traffic situation. In this study, we propose a variable speed limit framework based on connected vehicles environment to improve the management of non-recurrent congestion. The proposed framework is evaluated in terms of traffic efficiency, safety, and environmental impact using microscopic traffic simulation. Furthermore, economic evaluation of these strategies is performed to determine the financial feasibility of their implementation. The results indicate that the VSL system manage to improve traffic efficiency, safety and environmental impact during the incidents. However, it is found that the results depend on incident location and incident severity (number of lanes blocked, and the incident duration).

Impact of Variable Speed-Limit System on Driver Speeds during Low-Visibility Conditions

AbstractLow-visibility conditions can inhibit a driver’s ability to perceive appropriate operating speeds, particularly during foggy conditions in which the characteristics of the fog can vary spat...

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 use of advanced traffic information system to manage traffic congestion in developing countries

Abstract Presently, advanced traveler information system (ATIS) is extensively used elsewhere and is regarded as an important component for road traffic control and management. ATIS uses information and communication technology to broadcast traveler information to commuters to help them in scheduling their trips and also offer directions on the way. Information provided by ATIS may include: traffic condition (which may be presented in queue length, travel time, or delay), incidents such as road traffic crash and their geographical locations, events such as road construction and demonstrations, optimal routes, and inclement weather which may disrupt traffic. The traffic information may be transmitted via mechanisms such as radio and television, dynamic navigation systems (in-vehicle or mounted), internet services, smart phone services (e.g. specially designed application) and variable speed limit or changeable message signs systems. Providing commuters with accurate, timely and reliable traffic information will influence travel behavior and ultimately result in reduced travel time and traffic congestion along with reduced vehicle emissions and fuel consumption. Notwithstanding the benefits which can be derived from using intelligent transport systems to manage traffic, its use can be described as being in the basic stage in most developing countries. This paper discusses how ATIS can play a vital role of efforts to reduce traffic congestion in emerging nations.

Empirical evaluation of real-time traffic information for in-vehicle navigation and the variable speed limit system

Advanced traveler information systems (ATIS) present traffic information to travelers to assist them in planning their journeys and also provide guidance when on the road. Providing travelers with information affects travel behavior and can result in improved performance and reduced congestion and emissions. However, the success of ATIS depends on, among other factors, whether drivers consider it useful and their particular responses to the provided information. There are, currently, many sources and market players in the traffic information industry producing traffic reports for consumers. The main objective of this paper was to examine whether traffic information provided from different sources are consistent with one other. A variable speed limit system and real-time traffic information system for in-vehicle navigation systems are used as a case study. This comparative analysis was made by superimposing the space-time regions of ground truth measured traffic conditions (“reality”) over the space-time regions of the reported information broadcasts. A predictive buffer was also introduced in the assessment. The predictive buffer was included to account for traffic information which could be considered as advance warning messages or correctly predicting and giving congestion information prior to the onset of actual congestion, which otherwise may have been reported as false alarms. This was motivated by the fact that optimal control approaches include the prediction of congestion in their control strategies. The methods developed in this research work have been applied to a real world problem to prove its applicability.

Development of Benefit Cost Analysis Tools for Evaluating Transportation Research Projects

Transportation research projects are a vital element for transportation agencies to accumulate new technology and knowledge to improve the efficiency and safety of transportation infrastructure. The purpose of this paper is to develop benefit cost analysis (BCA) tools to assist transportation agencies in evaluating transportation research projects. The BCA tools provide analysis methods for estimating the benefits for changes in the level of service (LOS) of a roadway, reductions in the vehicle travel time, changes in vehicle operating costs and reductions in the number of crashes. Three case studies were investigated to illustrate the usage of the BCA tools. The first case study evaluated the effectiveness of variable speed limit systems implemented along I-80 in southern Wyoming. The BCA tools estimated a benefit cost ratio of 6.64 indicating that the implementation of the project was economically justifiable. The second case study was a recent study investigating and developing mitigation strategies for the effects of truck traffic along the I-80 in southern Wyoming resulting in a benefit cost ratio of a 9.23 indicating that the project had the potential to be economically viable upon implementation. The final case study evaluated the effect of wildlife overpass and underpass crossings on the migrations of pronghorn and mule deer. The benefit cost ratio for the research project was 0.42 indicating that the project was not economically beneficial after the first year of implementation. The case studies indicated that the BCA tools are a beneficial tool for quantifying the economic benefits of a transportation research project.

Bottleneck mitigation through a variable speed limit system using connected vehicles

ABSTRACTVariable speed limit (VSL) systems are used to improve the traffic conditions by adjusting the speed limits based on the current traffic situation. Advances in vehicle technology have made it possible to use connected vehicles in VSL systems. Connected vehicles can continuously transmit information about their speed and location, which can be used to estimate the current traffic conditions at arbitrary locations. In this study, we propose a VSL system based on connected vehicles. The aim is to also allow application of VSLs for non-recurrent bottleneck mitigation at arbitrary locations, unlike today's systems which require densely placed detectors or are limited to beforehand known bottleneck locations. The proposed system is evaluated by microscopic traffic simulation. The results indicate that the VSL system manage to improve traffic efficiency in a simulated incident scenario.

Characteristics of variable speed limit systems

The control algorithm used for deciding on the speed limit in variable speed limit systems is crucial for the performance of the systems. The algorithm is designed to fulfil the purpose of the variable speed limit system, which can be one or several of the following aspects: increasing safety, increasing efficiency and decreasing environmental impacts. Today, many of the control algorithms used in practice are based on fixed thresholds in speed and/or flow. Therefore, they are not necessarily reflecting the current traffic conditions. Control algorithms with a greater level of complexity can be found in the literature. In this paper, four existing control algorithms are investigated to conclude on important characteristics affecting the performance of the variable speed limit system. The purpose of the variable speed limit system and, consequently, the design of the control algorithm differ. Requirements of the investigated control algorithms are that they should be easy to interpret and the execution time should be short. The algorithms are evaluated through microscopic traffic simulation. Performance indicators related to traffic safety, traffic efficiency and environmental impacts are presented. The results show that the characteristics of the variable speed limit system and the design of the control algorithm will have effect on the resulting traffic performance, given that the drivers comply with the variable speed limits. Moreover, the time needed to trigger the system, the duration and the size of speed limit reductions, and the location of the congestion are factors of importance for the performance of variable speed limit systems.

Parametric Ordinal Logistic Regression and Non-Parametric Decision Tree Approaches for Assessing the Impact of Weather Conditions on Driver Speed Selection Using Naturalistic Driving Data

The impact of adverse weather conditions on transportation operation and safety is the focus of many studies; however, comprehensive research detailing the differences in driving behavior and performance during adverse conditions is limited. Many previous studies utilized aggregate traffic and weather data (e.g., average speed, headway, and global weather information) to formulate conclusions about the impact of weather on network operation and safety; however, research into specific factors associated with driver performance and behavior are notably absent. A novel approach, presented in this paper, fills this gap by considering disaggregate trajectory-level data available through the SHRP2 Naturalistic Driving Study and Roadway Information Database. Parametric ordinal logistic regression and non-parametric classification tree modeling were utilized to better understand speed selection behavior in adverse weather conditions. The results indicate that the most important factors impacting driver speed selection are weather conditions, traffic conditions, and the posted speed limit. Moreover, it was found that drivers are more likely to significantly reduce their speed in snowy weather conditions, as compared with other adverse weather conditions (such as rain and fog). The purpose of this study was to gather insights into driver speed preferences in different weather conditions, such that efficient logic can be introduced for a realistic variable speed limit system—aimed at maximizing speed compliance and reducing speed variations. This study provides valuable information related to drivers’ interaction with real-time changes in roadway and weather conditions, leading to a better understanding of the effectiveness of operational countermeasures.

Cycle‐based variable speed limit methodology for improved freeway merging

Studies and field implementations demonstrate that variable speed limit (VSL) systems help freeway traffic congestion mitigations. This study presents a cycle-based variable speed limit (CVSL) strategy that could variate speed limits in the upstream segment of freeway merging areas. CVSL reduces speed limits in a fraction of a cycle. This variation creates artificial gaps on freeway mainlines, which in turn increases merging opportunities for incoming on-ramp vehicles. CVSL retains VSL's benefit in reducing delays while overcoming its shortcoming of no significant throughput increase. The authors establish analytical CVSL delay models, including freeway mainline and ramp delays with CVSL speed as a decision variable, and propose a robotic solution method to minimise the delays. The delay model and solutions are implemented and independently evaluated in microscopic traffic simulation. Particularly, the CVSL system is implemented and interfaced with the transportation flow open-source microscopic model (ETFOMM). Detector information from ETFOMM is fed into the delay model, and the optimised speed limit is fed back to ETFOMM. Two performance measures, total travel delay and throughput, are used to evaluate the CVSL system. Their simulation evaluation indicated up to 16% delay reduction and 6% throughput increase. This CVSL strategy is ready for field evaluation.

Using connected vehicles in a variable speed limit system

Abstract Variable speed limit systems are used to improve the traffic conditions on specific road stretches. This is done by adjusting the speed limits according to current traffic situations. A variable speed limit system usually consist of stationary detectors to estimate the traffic state and variable message signs at predefined locations for the application of new speed limits. Advances in vehicle technology have made it possible to use connected vehicles to improve existing variable speed limit systems. Connected vehicles can continuously transmit information about speed and location. This can be used to get more detailed information about the traffic state. By including information from connected vehicles in a variable speed limit system there is a potential to identify bottlenecks also in between stationary detectors. Further, it is possible to use direct control of the connected vehicles to adjust vehicle speeds towards the new traffic situation. In this study, we propose such a variable speed limit system based on connected vehicles. The aim is to allow for application of variable speed limits in connection with non-recurrent bottlenecks. The proposed system is evaluated with respect to traffic efficiency using microscopic traffic simulation. An incident is simulated as an example of a non-recurrent bottleneck. The traffic performance when the proposed VSL system is applied is compared to the performance without the system. The results indicate that the VSL system manage to improve traffic efficiency in a majority of the simulated cases.

Simulation-based Variable Speed Limit Systems Modelling: An Overview and A Case Study on Istanbul Freeways

Abstract: Modern transportation systems aim at maximizing the use of available resources in a sustainable manner to deliver efficient and safe movement of traffic. Variable Speed Limit (VSL) system is one of the techniques adopted in order to improve mobility. In this study, we analyse this system using simulation techniques on a 5.2 kilometre section of Istanbul Freeway D100. Being one of the most congested cities in the world, Istanbul freeways provide an excellent opportunity to test the potential benefits of VSL systems. Latest advancements along with comprehensive literature of this field based on simulation are included in this study. Microscopic traffic simulation software VISSIM is used along with MATLAB to implement VSL algorithm based on volume, occupancy and average speed. Remote Traffic Microwave Sensor (RTMS) data is provided by Istanbul municipality which is used to calibrate VISSIM.Scenarios with and without VSL system were simulated for morning hours. It is concluded that driver compliance to VSLs is an important factor for better results. Although 100% driver Compliance Level (CL) for VSL results in significantly higher improvement in performance compared to lower compliance, it is not a practical approach therefore results at 75% and 50% CL has been discussed in this study. Evaluation of network performance is done in terms of Total Travel Time (TTT) in network along with volume, speed and occupancy. Results show reduction in TTT and occupancy level along with improvement in average speed and volume. Fuel consumption and emissions is also found to be reduced in the network indicating sustainable and environmental friendly mobility.

Pavement skid resistance consideration in rain-related wet-weather speed limits determination

Posted maximum speed limits used by highway agencies worldwide are typically applicable to dry-weather driving conditions. During wet weather, these speed limits may exceed the maximum speed for safe traffic operations. More and more highway agencies are employing variable speed limits as a means to improve wet-weather driving safety. For rain-related wet-weather conditions, the variable speed limit systems in use today commonly set speed limits based on either consideration of stopping sight distance, or past experience and engineering judgement. A common shortcoming of the existing systems is that the actual pavement skid resistance characteristics are not considered in setting the speed limits. This paper proposes an improved procedure to derive mechanistically the speed limits from the required safe stopping distance as well as the minimum skid resistance requirement for safe driving, based on the actual skid resistance properties of the pavement considered. The proposed procedure makes use of a finite-element skid resistance computer simulation model to determine both the available skid resistance values and vehicle braking distances at different vehicle speeds of the in-service pavement under specified rain-related wet-weather conditions. The procedure is theoretically sound, and is consistent with the concept of pavement network friction management system. In the analysis, the rain-related wet-weather condition is represented by rainfall intensity, and the road section is characterised by its gradient and cross slope, as well as the skid resistance properties of the pavement. A numerical example is presented to illustrate the working of the proposed procedure.

A Network-Wide Bilevel Optimization-Simulation Approach for Variable Speed Limit Systems to Improve Travel Time Reliability

AbstractTraffic congestion is a serious challenge that urban transportation systems are facing. Variable speed limit (VSL) systems are one of the countermeasures to reduce traffic congestion and sm...

Effectiveness Analysis of Variable Speed Limit Systems(VSL) in Work Zones based on Meta－analysis

Effectiveness Analysis of Variable Speed Limit Systems(VSL) in Work Zones based on Meta－analysis

Capacity and safety analysis of hard-shoulder running (HSR). A motorway case study

Operational motorway conditions can be improved by introducing traffic flow management and control systems, such as ramp metering (RM), high occupancy vehicle (HOV) lanes, real-time variable speed limits (VSLs), reversible lanes (RL), automated highway systems (AHS) and hard-shoulder running (HSR). The effects of such devices need to be examined in terms of capacity and safety. This paper examines the case study of the Italian motorway A22, which is supposed to be equipped with an HSR system implemented along 128km in order to reduce congestion with consequent improvement in levels of service (LOS). We studied the traffic processes (capacity, flow distribution between lanes, reliability, etc.) and estimated the expected capacity and safety conditions. These latter were studied with the method provided by the Highway Safety Manual (HSM), as well as by undertaking sensitivity analyses to quantify the expected changes in crash frequency at varying HSR activation hours (from 30 to 200h) in a year. It has been observed that HSR activation does not involve significant variations in the general safety conditions in the presence of a considerable capacity increase up to 35%. Moreover, have been identified the cases which require speed limit implementation (with VSLs system) in function of the values of reliability ϕ and velocity process V‾, and also suggested a speed limit sign system.

Optimal Variable Speed Limit Control System for Freeway Work Zone Operations

AbstractImproving operational safety and efficiency of variable speed limit (VSL) systems are the two core control objectives at work zone areas. In response to such need, this study presents a proactive VSL control model for freeway work zone operations. The proposed model uses an embedded macroscopic traffic flow model to predict the traffic state evolutions over the projected time horizon and to determine the optimal speed limits. In addition, Kalman filter is adopted to correct the prediction inaccuracy in a timely manner. To improve the safety of operations, this study proposes a new control objective function to smooth speed transition along the target freeway sketch by minimizing the difference between actual speeds and ideal speeds. Also, the smoothness of speed transition can help prevent the formation of shockwave and consequently enhance system’s operational efficiency. The authors’ numerical experiment with a calibrated Verkehr In Stadten–SIMulationsmodell (VISSIM) simulator reveals that the p...