Work Zone Optimization for Two-Lane Highway Maintenance Projects

Many work zones exist in the urban road network and have a great negative impact on city traffic. Finding the optimal work zone schedule can minimize the negative impact of work zones on traffic. This paper focuses on the day-based work zone scheduling problem in the urban network. Existing studies on the day-based work zone scheduling problem do not consider the progression of day-to-day traffic from a non-equilibrium state to an equilibrium state during the construction period. For the first time, this paper proposes a model for day-based work zone scheduling by introducing a day-to-day traffic assignment model, in which the target of the optimization problem is minimizing the increase in travel cost caused by work zones. Numerical examples are presented to explore the variations of the optimal construction sequence for different work durations, crew numbers, and model parameter values. Some new findings are obtained in the paper. When the construction duration of each work zone is relatively short (for example, less than 20 days), the optimal scheduling will obviously change with the work duration; when all of the construction durations increase to a threshold (for example, 60 days), the optimal construction sequence will no longer change. An optimal crew number exists that can minimize the increment of travel cost caused by work zones. During the construction period, the total travel cost in the network can be decreased by guiding travelers to change their original travel habits.

<b>Objective:</b> Work zone safety is one of the top priorities for transportation agencies. In recent years, a considerable volume of research has sought to determine work zone crash characteristics and causal factors. Unlike other non–work zone–related safety studies (on both crash frequency and severity), there has not yet been a comprehensive review and assessment of methodological approaches for work zone safety. To address this deficit, this article aims to provide a comprehensive review of the existing extensive research efforts focused on work zone crash-related analysis and modeling, in the hopes of providing researchers and practitioners with a complete overview.<b>Methods:</b> Relevant literature published in the last 5 decades was retrieved from the National Work Zone Crash Information Clearinghouse and the Transport Research International Documentation database and other public digital libraries and search engines. Both peer-reviewed publications and research reports were obtained. Each study was carefully reviewed, and those that focused on either work zone crash data analysis or work zone safety modeling were identified. The most relevant studies are specifically examined and discussed in the article.<b>Results:</b> The identified studies were carefully synthesized to understand the state of knowledge on work zone safety. Agreement and inconsistency regarding the characteristics of the work zone crashes discussed in the descriptive studies were summarized. Progress and issues about the current practices on work zone crash frequency and severity modeling are also explored and discussed. The challenges facing work zone safety research are then presented.<b>Conclusions:</b> The synthesis of the literature suggests that the presence of a work zone is likely to increase the crash rate. Crashes are not uniformly distributed within work zones and rear-end crashes are the most prevalent type of crashes in work zones. There was no across-the-board agreement among numerous papers reviewed on the relationship between work zone crashes and other factors such as time, weather, victim severity, traffic control devices, and facility types. Moreover, both work zone crash frequency and severity models still rely on relatively simple modeling techniques and approaches. In addition, work zone data limitations have caused a number of challenges in analyzing and modeling work zone safety. Additional efforts on data collection, developing a systematic data analysis framework, and using more advanced modeling approaches are suggested as future research tasks.

Critical road user safety deficiencies within road work zones across Sri Lanka are addressed in this research, where the construction and maintenance of transportation infrastructure significantly influence risk exposure. A comprehensive nationwide analysis revealed that widespread non-compliance with the national guidelines on traffic control for road work areas primarily contributed to elevated hazards. Core safety challenges identified include inadequate traffic control measures, insufficient illumination, absence or inadequacy of warning signage, inconsistent enforcement of safety protocols, and adverse geographic or environmental conditions. Crucially, the study diagnosed a fundamental methodological gap: inconsistent risk assessment by consulting engineers due to varying levels of expertise, subjective judgment, and the lack of a standardized, quantitative framework. This inconsistency impedes accurate identification of risk levels (high, medium, low) and hinders effective mitigation planning. To overcome these limitations, this study introduces a novel, intelligent risk assessment platform leveraging machine learning (ML) for the automated, objective, and consistently classified work zone safety levels. The core innovation lies in integrating mathematical rigor with real-world engineering validation. The methodology employed a mixed-method strategy across 40 representative work zones. Data encompassed detailed field surveys capturing physical conditions, traffic parameters, and compliance metrics, alongside expert insights. Risk was quantified along three key dimensions: severity, exposure, and likelihood. These indices were derived using a weighted Likert-scale system applied to observed risk factors. The calculated risk index level was identified through a clustering algorithm (K-means), which was then applied to these indices to empirically define high, medium, and low-risk categories, providing a data-driven baseline. Subsequently, multiple supervised ML algorithms were trained and optimized using the field data and the cluster-derived risk labels as ground truth. The primary task was classification into the predefined risk categories based on the input risk factor assessments. Crucially, model validation incorporated rigorous comparison against independent safety evaluations conducted by experienced engineering professionals. This ensured the ML platform's outputs aligned with practical, on-ground engineering judgment, bridging the gap between algorithmic prediction and real-world applicability. Results indicated a concerning prevalence of medium to high-risk classifications across the surveyed zones, confirming significant non-compliance with national standards, particularly regarding signage, lighting, and protective barriers. Among the ML models evaluated, the random forest algorithm demonstrated superior performance, achieving the highest classification accuracy while maintaining strong interpretability through feature importance analysis, making it optimal for field deployment. This research delivers a validated, intelligent ML-based platform that provides scalable, consistent, and objective safety assessments for road work zones in Sri Lanka. It directly addresses the identified problem of inconsistent engineer evaluations by offering a standardized, data-driven methodology. The platform calculates a composite risk index for work zones by integrating predictions from a random work zone model with an audited work zone database. This index, derived from input risk factors, classifies work zone risk into three levels: low (0 ≤ index &lt; 0.204), medium (0.204 ≤ index &lt; 0.298), and high (0.306 ≤ index ≤ 1). Using the established classification levels and developed platform, a comprehensive risk identification system was formulated based on variations in the risk index and its relationship with key factor combinations. This approach enables a dual-path risk identification method that enhances accuracy and reliability. The platform functions as a powerful decision-support tool for engineers, policymakers, and contractors, facilitating targeted and data-driven safety interventions. By integrating advanced analytics with domain expertise validation, the study delivers a significant technological advancement in road safety management. This robust solution holds particular relevance for Sri Lanka's extensive ongoing and planned highway infrastructure projects, supporting more informed and effective safety strategies.

Identifying risk factors for road traffic injuries can be considered one of the main priorities of transportation agencies. More than 12,000 fatal work zone crashes were reported between 2000 and 2013. Despite recent efforts to improve work zone safety, the frequency and severity of work zone crashes are still a big concern for transportation agencies. Although many studies have been conducted on different work zone safety-related issues, there is a lack of studies that investigate the effect of adverse weather conditions on work zone crash severity. This paper utilizes probit–classification tree, a relatively recent and promising combination of machine learning technique and conventional parametric model, to identify factors affecting work zone crash severity in adverse weather conditions using 8 years of work zone weather-related crashes (2006–2013) in Washington State. The key strength of this technique lies in its capability to alleviate the shortcomings of both parametric and nonparametric models. The results showed that both presence of traffic control device and lighting conditions are significant interacting variables in the developed complementary crash severity model for work zone weather-related crashes. Therefore, transportation agencies and contractors need to invest more in lighting equipment and better traffic control strategies at work zones, specifically during adverse weather conditions.

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.

Intelligent work zone (IWZ) systems use innovative technologies in real time to mitigate the negative impacts of work zones on the traveling public. The automatic queue detection (AQD) system is one type of IWZ being promoted by the Federal Highway Administration. Several field studies found that AQD systems were successful in reducing average travel speeds which led to a reduction in the number of rear-end crashes and in user costs. It has been shown that well-calibrated microsimulation models are appropriate analysis tools for traditional work zone traffic. To date, there are no tools in the literature that have been developed for AQD operations that have been calibrated and validated with empirical data. This paper aims to fill this gap by providing a comprehensive guideline for calibrating and validating a microsimulation model that can emulate traffic conditions and their impacts on freeway IWZ equipped with AQD systems. Specifically, the methodology includes (1) developing the base work zone model, (2) replicating the AQD warning messages, (3) calibrating the key simulation parameters using three types of data, and (4) validating the resulting simulation model using segment travel times. This comprehensive approach was demonstrated on a Nebraska work zone that was equipped with an AQD system. VISSIM simulation model was used for the underlying tool in the demonstration. The results presented in this paper are useful to both practitioners and scholars who wish to study the impact of the IWZ accurately through microsimulation.

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.

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] Work zones on highways have the potential to increase crash risk; therefore, efficient and noticeable signs play a critical role in enhancing highway safety. Some engineers have suggested that the traditional Manual on Uniform Traffic Control Devices (MUTCD) merge sign cannot be easily recognized by the driving public due to its graphical nature. In addition, the advance warning areas in work zones exhibit a higher crash rate than the transition, activity, and termination areas, therefore it is beneficial to focus on signage that will impact the advanced warning area of the work zone. A driving simulator is a virtual reality tool that can simulate different driving scenarios and can complement traditional field work due to its feasibility, safety, and cost-effectiveness. In this thesis, a driving simulator was applied to model six scenarios, including three different types of merge signs: MUTCD (baseline), MoDOT, and Quebec. Each merge sign was tested twice in both right lane closed and left lane closed work zone situations. The lane closure scenarios were alternated out of concern that participants might become accustomed to staying in one specific lane. Participants were randomly assigned to a different scenario sequence, thus avoiding sequence bias. A post-experiment survey and a motion sickness screening questionnaire were used to assess driver impressions of the signage and comfort level with the simulator. The results of both the experiment and survey showed that for three different merge signs, participants sustained comparable speeds when passing work zones. For the MoDOT sign, participants merged earlier into the open lane than they did with the other two signs. The MoDOT sign also resulted in the smallest standard deviation of merge location among the three signs. This means that participants reacted to the MoDOT sign consistently. The work zone with the MUTCD sign resulted in the highest speed differential between the merge location and the work zone lane drop taper. Even though 29.4 percent participants incorrectly perceived the meaning of MUTCD signs compared with only 3.7 percent for the other two signs, the participants who did correctly understand the MUTCD sign rated the sign positively.

The late merge traffic control strategy has been proposed as a way to improve flow at work zone lane closures by maximizing queue storage space and creating more orderly merging. The late merge instructs drivers to use all lanes to the work zone taper and then take turns proceeding through the work zone. There is little information available on when the late merge should be used, however, and a limited understanding of the factors that influence its performance. This paper discusses the results of a simulation study of the late merge concept using microscopic traffic simulation. The late merge concept was evaluated by comparing it with traditional traffic control, through a full factorial analysis. Results of the computer simulations showed that the late merge produced a statistically significant increase in throughput volume versus the traditional merge for the three-to-one lane closure configuration across all combinations of analysis factors. Although the two-to-one and three-to-two configurations did not show significant improvement in throughput overall, it was found that as the percentage of heavy vehicles increased, the late merge did foster higher throughput volumes than traditional traffic control. The results of the simulations indicate that the late merge may not provide as much of a benefit as previous studies had indicated and that the area of application for the late merge may be limited to situations where heavy vehicles constitute more than 20% of the traffic stream.

This study proposes a methodology for deriving the optimal work zone schedule for the annual routine maintenance planning in an infrastructure asset management system considering the (i) economies of scale in work zone costs due to work zone synchronization and (ii) user costs across the road network with traffic assignments. A key aspect of the proposed methodology is the ability to derive in detail optimal work zone schedules of realistic‐scale road networks in 100 m sections for 365 days, which is beneficial in practice. To this end, an optimization model of the work zone schedule is newly formulated as a mixed‐integer programming (MIP) problem, and a novel bilevel solution method for the model utilizing the conventional solver Gurobi Optimizer with MIP algorithms such as root relaxation, dual simplex, barrier methods, and cutting planes is proposed. In application examples, the proposed methodology is applied to two real‐world road networks, which confirms that the optimal work zone schedule can be obtained in 313.7 s for a network with 2640, 100 m, sections and in 168,180 s (46 h and 43 min) for a network with 5038, 100 m, sections.

Work zones are common for preservation and enhancement of roadways. Several efforts have been made to both improve safety for workers, especially, the flaggers, and reduce operational costs of work zones. In this paper, we investigate and prototype low-cost edge-AI enabled automated flaggers for traffic control to eliminate the need or reduce the number of human flaggers. To this end, we build a pair of connected portable traffic light units, each equipped with a camera, built-in microprocessor, portable battery and long-range WiFi radio for deployment at two ends of a work zone. We then develop an auto-flagger system with two modes: one semi-automated and the other fully-automated, by leveraging state-of-the-art deep learning and computer vision techniques. The semi-auto flagger system is trained to monitor and recognize hand-signals of a single human-flagger who stands at a safe location within the work zone, which then controls the two smart traffic light units. In the fully-automated flagging mode, the smart traffic light units collaboratively monitor and detect vehicles coming in and out of the work zone, and then decide on when to switch the traffic direction. We design a 4-phase automated work zone traffic control algorithm based on a collaborative leader-follower strategy. Finally, we experimentally validate the auto-flagger system on our connected and autonomous vehicle proving ground.

Safety of work zones is a major area of concern since it is not always possible to maintain a level of safety comparable to that of a normal highway not under construction. Proper traffic control is critical to the safety of work zones. However, traffic control devices themselves may pose a safety hazard when impacted by errant vehicles. The impact performance of many work zone traffic control devices is mostly unknown, and little, if any, crash testing has been conducted in accordance with guidelines set forth in NCHRP Report 350. The Texas Department of Transportation (TxDOT) has, in recent years, sponsored a number of studies at the Texas Transportation Institute to assess the impact performance of various work zone traffic control devices, including plastic drums and sign substrates, temporary and portable sign supports, plastic cones, vertical panels, and barricades. The results, findings, conclusions, and recommendations are presented for temporary and portable sign supports, plastic drums, sign substrates for use with plastic drums, traffic cones, and vertical panels, whereas those for barricades are covered elsewhere. Most of the work zone traffic control devices satisfactorily met the evaluation criteria set forth in NCHRP Report 350 and are recommended for field implementation. However, some of the devices failed to perform satisfactorily and are not recommended for field applications. The results from these studies are being incorporated into the TxDOT barricade and construction standard sheets for use in work zones.

Real-time merging traffic control for throughput maximization at motorway work zones

State departments of transportation (DOTs) develop traffic control plans (TCPs) as part of construction projects. TCPs communicate required traffic control measures to the construction team and help ensure safe travel through construction work zones and a safe environment for construction workers. TCP quality can vary from project to project as a result of many factors, including the process by which the TCP is designed, reviewed, implemented, and inspected; the features and layout of the TCP and roadway; and the communication of the TCP to the constructor. This paper presents a research study conducted to understand how to improve work zone safety performance by improving the TCP design and implementation processes, identifying the TCP and roadway attributes that made TCP implementation challenging, and identifying factors that affected TCP quality and consistency. A sample of 39 construction projects of varying types and sizes was studied with a mixed methods research approach that included a survey of 12 key personnel on each project, a quantitative evaluation of each project's TCP, analysis of project crash data, and an on-site evaluation of the work zone. TCP quality and consistency and worker and motorist safety were found to be higher on projects for which constructability reviews and design peer reviews had been conducted and on projects on which the contractor super intendent and TCP designer had more years of experience and had undergone specialized TCP training. The TCP features found to increase TCP complexity to the greatest extent were multiple traffic control stages, multilane closures, and dense temporary signage.

Construction sites or work zones create serious disruptions in the normal flow of traffic, resulting in major inconveniences for the traveling public. Furthermore, these work zones create safety hazards that require special consideration. Current legislation and programs, at both state and national levels, emphasize the need for a better understanding of work zone problems to address work zone safety. This reality—coupled with the temporary closure of more miles of highway every year for rehabilitation and maintenance—makes the analysis of safety at construction sites a serious matter. A summary of a comprehensive study associated with the development of a new practical approach to address highway safety in construction zones is presented. Because empirical models require sample sizes that are not attainable due to the intrinsic scarcity of construction zone accident data, the problem was studied from the point of view of risk analysis. Monte Carlo simulations were used to develop risk factors. These factors are meant to be included in the calculations of additional user costs for work zones, or simply applied as risk measurements, to optimize the length and duration of closures for highway reconstruction and rehabilitation projects. In this way, it will be possible to assess the danger of work zones to the traveling public and minimize adverse effect of work zones on highway safety.