Simulation and Analysis of the Variable Speed Limit Controls on Highway Maintenance

Variable speed limit (VSL) systems are important active traffic management tools that are being deployed across the U.S. and indeed around the world for relieving congestion and improving safety. Oregon’s first variable advisory speed limit signs were activated along Oregon Highway 217 in the summer of 2014. The variable advisory speed system is responsive to both congestion and weather conditions. This seven-mile corridor stretches around Western Portland and has suffered from high crash rates and peak period congestion in the past. VSL systems are often deployed to address safety, mobility and sustainability related performance. This research seeks to determine whether the newly implemented variable advisory speed limit system has had measurable impacts on traffic safety and what the scale of the impact has been. The research utilizes a before-after crash analysis with three years of data prior to implementation and around 16 months after. Statistical analysis using an Empirical Bayes (EB) approach will aim to separate the direct impacts of the variable advisory speed limit signs from the long term trends on the highway. In addition, the analysis corrects for the changes in traffic volumes over the study period. Three data sources will be utilized including Washington County 911 call data, Oregon incident reports, and official Oregon Department of Transportation crash data reports. The analysis results are compared between data sources to determine the reliability of 911 call data as a proxy for crash statistics. The conclusions should be able to provide an indication of whether variable advisory speed limits can provide increased safety along high crash corridors.

The study examined Measures of Effectiveness (MOE) of vehicle speeds and its comparison with posted speed limits in Advance Warning Zone (AWZ), Working Zone (WZ) and Terminal Transition Zone (TTZ) on NH-8 in India. Results indicate that (1) except slow moving vehicles, all the fast moving vehicles exceeded the posted speed limit of 40 km/h in AWZ and WZ; (2) 85th percentile speeds of Cars/Jeeps, Two-wheelers, Standard Trucks, Mini Trucks, and Buses are much higher than speed limit in AWZ and WZ; (3) mean speeds of fast moving vehicles are more than speed limit in AWZ and WZ; (4) there is no significant difference in the speed of vehicles in AWZ, WZ and TTZ at 95% confidence interval. This study strongly recommends the use of active traffic calming measures like Rumble Strips on Highway Work Zones.

A variable speed limit model for freeway bridges considering the influence of both traffic service level and visibility in fog

This study employs a Vissim–Matlab component object model (COM)-based microsimulation model to evaluate the effectiveness of variable speed limit (VSL) strategies during traffic incidents. This study examines two VSL strategies on a 2.7 km section of Thailand’s Motorway No. 7: VSL1 with 1 km spacing and VSL2 with 2 km spacing. Simulation results show that under peak volume conditions, the VSL1 strategy outperforms both the existing scenario and VSL2 in terms of traffic performance and safety. This advantage holds for single-lane closures for both short and long periods. However, for two-lane closures with prolonged incident-clearance times, the VSL system should be temporarily deactivated to prevent increased congestion. Sensitivity analysis results indicate that under mild to moderate traffic volumes, VSL1 and VSL2 perform similarly in both traffic performance and safety across single- and double-lane closures and both closure durations. Both strategies outperform the existing scenario in nearly all cases. The VSL implementation yielded up to an 18% increase in average speed and an 88% reduction in rear-end conflicts. The magnitude of these improvements increased as traffic demand decreased. However, under congested conditions with two-lane closures, the VSL system should remain inactive regardless of the expected incident-clearance time.

Variable Speed Limits (VSL) are primarily designed to enhance traffic safety on hazardous roadways by dynamically adjusting speed limits based on real-time traffic and weather conditions. Most previous studies have focused on using VSLs to improve safety, mitigate congestion, and reduce environmental impact, assuming a securely connected VSL network. But what would be the impact of cyberattacks on VSL systems on traffic safety and network efficiency. This paper investigates the impact of intentional disruptions on VSL signs within traffic networks. We present a threat model to identify vulnerabilities in the VSL communication network and potential access points for attackers. An analytical accident model was developed, and various VSL disruption scenarios were simulated using a case study of Highway 1 in British Columbia, Canada, in SUMO (Simulation of Urban MObility) to assess the potential for crashes and safety problems resulting from VSL disruptions. Surrogate Safety Measures (SSM) were employed as key measures of safety concerns. Our findings highlight notable risks, including up to 56% additional conflicts, posed by these intentional disruptions. A robustness assessment using Monte Carlo simulation runs of a scenario with heterogeneous driver behaviors demonstrated that the safety impact is consistent and not random seed-dependent. Across runs, intentional disruptions still yielded significant increases in conflicts, with an average rise of 24.95%, confirming the stability of the results. Various mitigation strategies are discussed to enhance traffic safety and resilience against VSL manipulation.

Objective: To assess driving behavior when presented with different work zone features such as signs. Driving behavior upstream of a work zone is of interest since this is the point where drivers need to slow or react to upcoming conflicts such as lane closures, congested traffic, or presence of workers and equipment.Methods: Using 299 time series traces from four-lane roadways with both shoulder and lane closure scenario from the naturalistic driving study, this study analyzed driving behavior by detecting response points within the advance warning area from the first sign to the start of work zone. Response point was defined as the point where drivers reduced speed by a certain threshold. A mixed effect logistic model was developed to assess the relationship between driver response and work zone characteristics.Results: Results indicated the first work zone sign a driver encountered in the immediate area upstream of the work zone was not significantly likely to elicit a driver response. The model found lane ends, speed limit, and active changeable message signs (CMS) as statistically significant. Since more than one sign can be legible to the driver at the same time, the effect of overlapping signs was evaluated, but was not found to have significant effect on the driver response. In general, drivers were more likely to show a response to the signs the closer they got to the start of the work zone. Static work zone speed limit and dynamic speed feedback signs were both found to be more likely to elicit a response as compared to normal speed limit signs (non-work zone related). Drivers who were traveling over the posted speed limit were more likely to show response at any given work zone signs with the exception of the first sign. In addition, driver distraction, and driver information like age, gender, experience and other environmental factors were not found to be significant in the model.Conclusions: Overall, drivers were likely to show a response at the lane ends, work zone speed limit signs, and speed feedback signs.

Freeway work zones with lane closures can cause traffic disruption and congestion with increased travel time, safety risks, and emissions.Variable speed limit (VSL) control has been widely studied to mitigate the negative impacts of work zone lane closures.To ensure effective VSL control, accurate detection of traffic conditions is important.However, stationary sensors from distant upstream or merging areas of a work zone can only provide location-based detections, which may not be sufficient for effective VSL control.Therefore, this study proposes a VSL control system for a smart work zone with a weighted traffic density estimation algorithm using data from stationary sensors and connected vehicles (CV).With location-based traffic detections from distant upstream and merging areas of a smart work zone, data from CVs in locations between the stationary sensors are used to obtain the weighted density.This weighted density is then fed to a feedback VSL controller, which can dynamically define the appropriate speed limits to reduce the negative impacts of the work zone closures.The proposed VSL controller was implemented and evaluated under a calibrated freeway work zone environment using the traffic simulator SUMO.The results show that the system can provide accurate traffic density estimation and effectively improve traffic mobility, safety, and environmental sustainability near the work zone area.

This paper provides an overview of various variable speed limit (VSL) strategies developed over the last two decades. It first explains the theoretical background of VSL systems and how they can be used as dynamic traffic control devices to improve traffic conditions and increase safety. An overview of VSL control strategies, ranging from early rule-based approaches to the most advanced network-wide coordinated approach, is provided, followed by a discussion of their associated potential benefits and areas for improvement. The likely environmental benefits of VSL strategies are also discussed, along with some further related aspects of VSL application, such as driver compliance to VSL and the integration of a differential speed limit (DSL) with VSL. Finally, the paper presents a critical review, pointing out some key issues that were identified from the literature review and recommends some directions for future research that need to be addressed as recommendations for best practices to underpin further refinement, development, and application of VSL.

Transportation professionals view the setting of appropriate regulatory speed limits on public roads, including those under repair or reconstruction, as an important tool in promoting safe and efficient operations. The Ohio Department of Transportation sponsored a study to evaluate its work zone speed zoning processes. Researchers observed motorists' speed choices upstream of and adjacent to several combinations of work zone conditions and factors that were used to justify reduced speed limits in Ohio work zones. Researchers also observed motorists' speed choices upstream of and within pilot variable work zone speed zones. Researchers confirmed that motorists reduced their speed only if they clearly perceived a need to do so. Therefore, whenever possible, the first work zone speed limit sign should be installed within view of a work zone condition. In general, the speed reduction downstream of the first nonvariable and variable work zone speed limit signs ranged from 1 to 6 mph and 3 to 11 mph, respectively. In addition, researchers found that the speed reduction on entering a lane shift, within a lane closure, and on entering a median crossover ranged from 4 to 15 mph. On the basis of previous research and the results of the studies documented in this paper, the research team developed work zone speed zone guidelines for multi-lane highways with original posted speed limits greater than or equal to 55 mph. Researchers also made recommendations for where variable work zone speed zoning should be considered.

Recent research has investigated the effects of var iable speed limits (VSL) on traffic flow processes. Findings show that VSL profoundly impact lane flow distribution (LFD) and increase the use of the slow lane by reducing the speed difference between the slow lane and the overtaking lanes. Finally, VSL reduce the capacity drop phenomenon on multi-lane sections and significantly increase the proportion of flow on the slow lane. These results highlight the major impact of LFD on the ca pacity of multi-lane sections. The paper presents a new analytical model that esti mates the capacity of multi-lane sections and repro duces the capacity-drop caused by LFD characteristics. It can be applied to estimate the capacity of motorway se ctions with two or three lanes under common traffic condit ions; it can also estimate the impact of VSL on the capacity of multi-lane sections. The multi-lane capacity model is coupled with a dyn amic mesoscopic traffic flow model initially design ed for network applications: the meso-LWR model. The resulting dynamic traffic flow model is relevant for mot orway network applications and VSL evaluation. The dynamic model is implemented on a French motorway site. The results show the ability of the model to reproduce actual traffic situations (capacity, congestion per iod, etc.) without VSL, including the amplitude of capacity dr op phenomenon caused by the under-use of the slow lane. It also shows the ability of the model to estimate the effect of VSL on future traffic flow conditions.

Pakistan has a population of over 199 million and total road network of approximately 264,400 kilometers that serve about 16.2 million vehicles of all types. According to WHO estimates, there were approximately 30,000 annual Road Crash Fatalities (RCF) in Pakistan in year 2010. Work zone crashes account for significant proportion of all traffic crashes in Pakistan due to higher crash rate as compared to other parts of the highway network. Highway work zone is referred to road area where highway construction, maintenance or activity related to utility maintenance takes place. Workers in highway work zone are exposed to a variety of hazards and face risk of injury and death from construction equipment as well as passing motor vehicles. Safety measures and better understanding of risks involved while moving through the work zone have significant effects on the overall safety climate at work zones. Mismanaged work zone traffic increases the travel time delays, safety issues, vehicle operating costs (VOC) and other associated costs. Performance measures for the work zone traffic management includes user costs (travel time delay, crash cost, VOC), incident response and clearance time, queue length and community complaint. Different work Zone Traffic Management methodologies are being practiced worldwide and extensive research has been carried out at international level on country specific highway work zone safety but in Pakistan very few studies have been carried out on highway work zones. This research aims to critically analyze the impacts of the different Work Zone Traffic Management methods and recommend the best option for Expressways / Motorways in Pakistan. For the purpose of research, the author has selected a section of Motorway (M-2). Two different work zone traffic management methods are being followed in rehabilitation of M-2 .i.e. Parallel / Adjacent Method and Median Cross-Over Method. Performance measures selected for purpose of analysis are Travel Time Delay, Crash Cost (Safety) and VOC and data collected on section of M-2. After critical analysis, it is concluded that Parallel/ Adjacent Method results in lesser Travel Time delay and lesser VOC due to higher operating speeds and thus has higher savings, whereas Median Cross over Methods yield more Crash Cost savings. Keeping in view the driving habits / skills, poor maintenance of vehicles in Pakistan and risk of fatal accidents involved in parallel /adjacent method, median cross over method is preferred.

The prevailing variable speed limit (VSL) systems as an effective strategy for traffic control on motorways have the disadvantage that they only work with static VSL zones. Under changing traffic conditions, VSL systems with static VSL zones may perform suboptimally. Therefore, the adaptive design of VSL zones is required in traffic scenarios where congestion characteristics vary widely over space and time. To address this problem, we propose a novel distributed spatial-temporal multi-agent VSL (DWL-ST-VSL) approach capable of dynamically adjusting the length and position of VSL zones to complement the adjustment of speed limits in current VSL control systems. To model DWL-ST-VSL, distributed W-learning (DWL), a reinforcement learning (RL)-based algorithm for collaborative agent-based self-optimization toward multiple policies, is used. Each agent uses RL to learn local policies, thereby maximizing travel speed and eliminating congestion. In addition to local policies, through the concept of remote policies, agents learn how their actions affect their immediate neighbours and which policy or action is preferred in a given situation. To assess the impact of deploying additional agents in the control loop and the different cooperation levels on the control process, DWL-ST-VSL is evaluated in a four-agent configuration (DWL4-ST-VSL). This evaluation is done via SUMO microscopic simulations using collaborative agents controlling four segments upstream of the congestion in traffic scenarios with medium and high traffic loads. DWL also allows for heterogeneity in agents’ policies; cooperating agents in DWL4-ST-VSL implement two speed limit sets with different granularity. DWL4-ST-VSL outperforms all baselines (W-learning-based VSL and simple proportional speed control), which use static VSL zones. Finally, our experiments yield insights into the new concept of VSL control. This may trigger further research on using advanced learning-based technology to design a new generation of adaptive traffic control systems to meet the requirements of operating in a nonstationary environment and at the leading edge of emerging connected and autonomous vehicles in general.

Variable speed limits (VSLs) have a potential to improve mobility and safety of motorway through harmonisation of traffic flow. However, the success of VSL is highly dependent on drivers’ compliance to the displayed speed limits. Emerging technologies in the field of connected autonomous vehicles (CAVs) is likely to revolutionise the way VSL will be operated in the near future. VSL can be integrated with CAVs where CAVs will automatically obey the displayed speed limits. However, 100% penetration rate of CAVs is a long‐term goal. At the initial stage of deployment, CAVs will coexist with manually driven vehicles on motorways. This study explores ways to implement VSL under a mixed traffic condition where CAVs and manually driven vehicles coexist in the traffic stream. A hybrid approach combining particle swarm optimisation with proportional‐integrated‐derivative is proposed to improve VSL implementation under a range of mixed traffic conditions. The simulation results showed that the proposed method successfully achieved the desired speed limits and rapidly stabilised the system at the initial and transient points at penetration rates of 50 and 75%, whereas the method encountered serious overshoots at lower penetration rates.

The higher contribution of traffic delay to environmental impacts is urging the highway agencies to take work zone management into the maintenance schemes decision-making. Aiming to understand the role of work zone management in user CO2 emissions reduction, this paper firstly developed a practical methodological framework of traffic delay-related CO2 emissions caused by highway maintenance based on a popular life cycle user cost analysis approach in regard of the microscopic vehicle operation analysis. The method was applied in an actual freeway flexible pavement with 15-year design life in Shaanxi Province, China, covering three types of preventive maintenance, correction maintenance, and rehabilitation. In addition, the impacts of key inputs of proposed method on work zone user CO2 emissions results were checked. The results show that traffic delay attributes to 29.4% of total CO2 emissions of the life cycle of highway pavement maintenance, and 51.8% of work zone user CO2 emissions result from preventive maintenance, especially from micro vehicle operations including speed change and queue near work zone (62% of total work zone user CO2 emissions). The work zone management alternative strategies related to less traffic volume or higher highway capacity including vehicle type limitation and the limited work zone speed have an advantage in reducing the work zone CO2 emissions over changing work zone length or work zone timing. The findings in this paper may present a useful tool and reference for robustly supporting the decision-making on highway maintenance carbon mitigation in work zone traffic.

Dynamic areas strategy design for variable speed limiting at fixed freeway bottlenecks