Work Zone Operations Research Articles

Impact of Platooning Connected and Automated Heavy Vehicles on Interstate Freeway Work Zone Operations

Work zones pose mobility issues to the traveling public and safety challenges to travelers and road maintenance workers. These safety and mobility issues may be exacerbated by the presence of heavy vehicles. Connected and automated vehicle (CAV) technologies have been identified as a potential solution for these issues. This paper investigates the operational impacts of connected and automated heavy vehicles (CAHV) on freeway work zone operations on interstate highways. A microsimulation model, calibrated to empirical work zone field data, was used to study the operational impacts of CAHV platoons under various work zone and traffic conditions. It was found that, as the CAHV market penetration rate increases, the average work zone delay and queue length decreases. In addition, as the demand and heavy vehicle percentage increases, so do the benefits of using CAHV technology. For example, it was found that, when all heavy vehicles are classified as CAHV, the average flow rate is approximately 67% higher, and the maximum queue size and average delay decrease by approximately 97%. The methodology used in this paper will help transportation agencies as they design work zones to accommodate heavy vehicles equipped with CAV technologies.

Prediction of Queue Dissipation Time for Mixed Traffic Flows With Deep Learning

Queue dissipation has been extensively studied about traffic signalization, work zone operations, and ramp metering. Various methods for estimating the intersection’s queue length and dissipation time have been reported in the literature, including the use of car-following models with simulation, vehicle trajectories from GPS, shock-wave theory, statistical estimation from traffic flow patterns, and artificial neural networks (ANN). However, most of such methods cannot account for the impacts of interactions between different vehicle types and their spatial distributions in the queue length on the initial discharge time and the resulting total dissipation duration. As such, this study presents a system, named TrafficTalk, that applies a deep learning-based method to reliably capture the queue characteristics of mixed traffic flows, and produce a robust estimate of the dissipating duration for the design of the optimal signal plan. The proposed TrafficTalk, featuring the effectiveness in transforming video-imaged traffic conditions into vehicle density maps, has proved its performance under extensive field evaluations. For instance, compared with the benchmark model, XGBoost in the literature, it has reduced the MAPE from 25.8% to 10.4%., and from 31.3% to 10.4% if the queue discharging stream comprises motorcycles.

Inferring the causal effect of work zones on crashes: Methodology and a case study

The increasing number of crashes occurring in work zones has received considerable attention in recent years. Previous studies have mainly focused on associations between work zone configurations and crash occurrence. Although identification of associational relations helps us understand how work zones co-exist with crashes, it does not provide interventional guidelines necessary to improve safety of work zone operations. In this paper, a causal inference model based on the potential outcome framework is proposed to rigorously infer the causal effects of work zone presence on crash risks under various work zone configurations, along with robustness tests. In developing such a causal model, three research gaps are identified and addressed: (1) potential confounding bias due to unobservable roadway characteristics; (2) potential bias caused by unobserved variables in multisource data; and (3) lack of actually observed traffic data and weather information at the exact time when a crash occurred and lack of large-scale high-granular data. The proposed methodology is applied to 5,006 work zones in Pennsylvania from 2015 to 2017, and the results are validated via a series of robustness tests. The results show that the causal effect of a work zone on crash occurrence is significantly positive, especially on roadways with high traffic volumes, on long-distance work zones, and work zones conducted during daytime. It appears that conducting work zones during nighttime with the current deployment strategies on Pennsylvania state roads does not necessarily increase crash risks, but a work zone significantly increases crash risks during day time.

Dynamic Lane-Based Signal Merge Control for Freeway Work Zone Operations

AbstractTraditional merge control strategies cannot yield the expected effectiveness under heavy traffic conditions at freeway work zones because inevitable traffic conflicts resulting from complex...

A Platooning Strategy for Automated Vehicles in the Presence of Speed Limit Fluctuations

Platooning is expected to enhance the efficiency of operating automated vehicles. The positive impacts of platooning on travel time reliability, congestion, emissions, and energy consumption have been shown for homogenous roadway segments. However, the transportation system consists of inhomogeneous segments, and understanding the full impacts of platooning requires investigation in a realistic setup. One of the main reasons for inhomogeneity is speed limit fluctuations. Speed limit changes frequently throughout the transportation network, due to safety-related considerations (e.g., changes in geometry and workzone operations) or congestion management schemes (e.g., speed harmonization systems). In the current transportation systems with human-driven vehicles, these speed drops can potentially result in shockwave formation, which can cause travel time unreliability. Automated vehicles, however, have the potential to prevent shockwave formation and propagation and, therefore, enhance travel time reliability. Accordingly, this study presents a constant time headway strategy for automated vehicle platooning to ensure accurate tracking of any velocity profile in the presence of speed limit fluctuations. The performance of the presented platooning strategy is compared with Gipps’ car-following model and intelligent driver model, as representatives of regular non-automated vehicles. Simulation results show that implementing a fully autonomous system prevents shockwave formation and propagation, and enhances travel time reliability by accurately tracking the desired velocity profile. Moreover, the performance of platoons of regular and automated vehicles is investigated in the presence of a speed drop. The results show that as the market penetration rate of automated vehicles increases, the platoon can track the velocity profile more accurately.

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...

Analysis of work zone rear-end crash risk for different vehicle-following patterns

This study evaluates rear-end crash risk associated with work zone operations for four different vehicle-following patterns: car–car, car–truck, truck–car and truck–truck. The deceleration rate to avoid the crash (DRAC) is adopted to measure work zone rear-end crash risk. Results show that the car–truck following pattern has the largest rear-end crash risk, followed by truck–truck, truck–car and car–car patterns. This implies that it is more likely for a car which is following a truck to be involved in a rear-end crash accident. The statistical test results further confirm that rear-end crash risk is statistically different between any two of the four patterns. We therefore develop a rear-end crash risk model for each vehicle-following pattern in order to examine the relationship between rear-end crash risk and its influencing factors, including lane position, the heavy vehicle percentage, lane traffic flow and work intensity which can be characterized by the number of lane reductions, the number of workers and the amount of equipment at the work zone site. The model results show that, for each pattern, there will be a greater rear-end crash risk in the following situations: (i) heavy work intensity; (ii) the lane adjacent to work zone; (iii) a higher proportion of heavy vehicles and (iv) greater traffic flow. However, the effects of these factors on rear-end crash risk are found to vary according to the vehicle-following patterns. Compared with the car–car pattern, lane position has less effect on rear-end crash risk in the car–truck pattern. The effect of work intensity on rear-end crash risk is also reduced in the truck–car pattern.

Grocery retail operations and automotive logistics: a functional cross-industry comparison

Purpose – The purpose of this paper is to identify and describe similarities between logistics structures and mid-term planning problems in the grocery retail and automotive industries in a specific internal section of their respective supply chains. Design/methodology/approach – The benchmarking approach is used as a framework for this paper. It is based on insights resulting from several joint projects with grocery retailers and automobile producers. A particular focus of the research was participating in an exchange of ideas and experience between logistics managers in both industry sectors. Findings – The authors have identified parallels when comparing the internal retail supply chain of the grocery retail industry, which consists of distribution centres, transportation and in-store logistics, with the internal logistics network in the automotive industry, which consists of logistics supermarkets, transportation and work zone operations at the assembly line. Strong similarities have been found for three planning problems related to tactical planning tasks: assigning products and parts to delivery modes, selecting packaging units and loading carriers, and determining delivery cycles. In comparison to retailing, there is a clearer trend in the automotive industry to plan line-back and align processes with the operator's requirements at the assembly line. Practical implications – For logisticians in grocery retailing and the automotive industry, this paper provides relevant input for functional benchmarking initiatives and offers an inspirational view beyond the horizon. Originality/value – This paper is the first to focus on similarities in logistics network structures and planning tasks between the two industries from the viewpoint of grocery retailing.

Evaluation of Work Zone Strategies at Signalized Intersections

Reducing congestion in work zones and improving mobility has become more crucial than ever especially with the increased number of road projects. Work zones at street intersections are costly due to the delay experienced by both contractors and motorists. Work zones at signalized intersections are needed in the case of new construction, re-building the signal, or maintaining an existing traffic. This type of work can significantly affect traffic operations at intersections. Any lane reduction due to the construction zones will result in significant congestion. Another alternative is to reduce the existing lanes width and the speed limit instead of closing lanes. Although the literature shows statistics on work zone operations especially on freeways, there is a lack of information about signalized intersections. The purpose of this paper is to compare the amount of motorist delay that would accrue along the work zone from two strategies. Alternative 1 is based on reducing the number of lanes at the intersection and Alternative 2 is based on reducing lanes' width and maintaining the number of lanes at the intersection. The conducted methods showed that Alternative 2 provided better system operational performance than Alternative 1 for the cases tested. 

Estimation of Effectiveness of a Vehicle-Actuated Signal Control System on Work Zone Operations for a Two-Lane Highway

Korean two-lane highways take charge of a function to connect arterial roads with major national roads and provide efficient mobility. However, the number of work zones for road construction and expansion is constantly increasing owing to increment of traffic volume. Therefore the number of maintenance projects is also growing to meet the increased need for road maintenance. All projects that require full or partial closure of a two-lane highway create safety problems, because of two-way delays and poor traffic control, especially at night. Flagging is typically used to control traffic in work zones on two-lane highways by closing one lane and alternating traffic movements. Generally, there is a flagger or Time of Day (hereinafter TOD) control and a one- or two-way delay occurs. Poor safety control in work zones can result in a serious accident if a driver has poor visibility. In this study, to diminish these problems, some alternative traffic control systems are indicated such as actuated signal control with fixed all red (hereinafter AFAR) and actuated signal control with dynamic all red (hereinafter ADAR). And the comparison with each traffic control methods is analyzed focused on average control delay and the number of conflicts which take into account various situations as the length of work zone and traffic volume. The signal control methods under investigation were TOD, AFAR, and ADAR. The average control delay per vehicle was used to evaluate the effectiveness of each method, and work zone conflict was used to evaluate safety. ADAR was found to be the most efficient signal control method under most conditions examined, in terms of safety and mobility in work zones on two-lane highways.

Truck-Mounted Changeable Message Signs with Symbols for Work Zone Operations

Truck-mounted changeable message signs (TMCMSs) are desirable for scheduled and unscheduled short-duration work operations to inform drivers of unexpected conditions. Temporary traffic control for short-duration operations has been limited traditionally to arrow boards and static warning messages mounted to the work vehicle. With advances in technology, TMCMSs can fill a gap and provide drivers with better information about short operations and required actions by the driver. Through a study in a human factors laboratory, researchers evaluated message designs that incorporated text and graphic alternatives to warn drivers about accidents, work zone areas, and lane closures. In this study, researchers determined many key points about motorist interpretations of TMCMS symbols and text messages. The study found that (a) the accident symbol was well understood and enhanced motorists' abilities to recall the situation during limited viewing times, (b) the sign with the “Man Working” figure without the diamond background outline was recommended because it elicited the best reaction time by study participants, and (c) the lane-blocked symbols worked well to communicate lane conditions to drivers.

Enhanced Analysis of Work Zone Safety through Integration of Statewide Crash and Lane Closure System Data

Highway work zones interrupt regular traffic flow and lead to more severe types of crashes, as shown by many studies. In 2009 alone, more than 600 fatalities nationally were work zone related. Analysis of work zone safety can help to identify the risk factors and improve safety; such an analysis requires the consideration of a variety of data sources, including the frequency of crashes in and around a work zone and specific work zone characteristics. The traditional approach, in Wisconsin and many other states, has relied on the presence of a construction zone flag in the crash report and information from targeted work zone studies. The crash report provides a macroscopic view of work zone crashes but does not provide details about the work zones, except when noted in the police officer's narrative description. Targeted work zone studies provide a wealth of information for specific work zones but are limited in number and scope. The Wisconsin Lane Closure System (WisLCS), a centralized scheduling and reporting system for highway lane closures statewide, provides a new opportunity to match crashes to specific work zones on a systemwide level. This paper investigated the ability to match highway crash records from the Wisconsin Department of Transportation to WisLCS lane closure records. A preliminary analysis of work zone safety based on WisLCS closure attributes is presented and verifies the benefits of integrating work zone information. This knowledge can lead to safer work zone operations and planning decisions. The general ideas of this study can also be applied to any similar sets of crash and work zone data.

Categorization of Work Zone Intrusion Crashes

Vehicle intrusion crashes in highway work zones injure vehicle occupants and workers alike, and such crashes are the concern of both state agencies and highway contractors. This paper describes the results of an effort to develop prototypical scenarios of common work zone intrusion crashes documented in the New York State Department of Transportation work zone accident database. A prototypical scenario can be defined as one that is representative of the crash process because of the typicality of its chain of events and the likely causal relationships throughout the stages of the crash. By considering the chain of events that led to a particular crash, it is possible to group similar crashes and provide a more in-depth assessment, even though some of the facts involved in the individual crashes vary. In the study described here, prototypical scenarios were developed for four intrusion crashes at four types of work zone operations: lane closures, flagging operations, mobile operations, and traffic control setup and removal activities. It was concluded that a significant portion of intrusion crashes resulted from deliberate driver decisions and actions to enter the work space. The frequency of such deliberate events, which ranged from 25% to 64%, depended on the type of work operation in place on a given roadway. The study identified between three and eight prototypical crash sequences that were not the result of deliberate actions by drivers and that led to intrusion crashes.

Lane-Based Dynamic Merge Control Strategy Based on Optimal Thresholds for Highway Work Zone Operations

Despite the potential effectiveness of the dynamic late merge (DLM) control, most existing DLM systems, based on static thresholds, cannot best perform under time-varying traffic conditions. This paper presents an advanced dynamic merge control, called a lane-based dynamic merge control model and its operational algorithm, which is based on the optimized control thresholds that take into account the interactions among the speed, flow, and available work zone capacity. The focus of this study is on how to select the control variables and to determine their optimal thresholds in response to traffic flow dynamics. Evaluation results with extensive simulation experiments have shown the promising properties of the proposed dynamic merge control and its operational algorithm.

Simulation-Based Study on a Lane-Based Signal System for Merge Control at Freeway Work Zones

This paper presents a new lane-based signal merge (LBSM) control system for freeway work zone operations. The proposed system applies the signal control concept to regulate the vehicles passing the work zone area at a lane-by-lane basis and offers an effective way to maximize the operational efficiency as well as safety. Introduction of the preliminary configuration and principal components associated with the proposed LBSM control contribute the core of this study. To evaluate the effectiveness of the proposed system, this study has also conducted extensive simulation experiments, based on a freeway simulator calibrated with real-world work zone data. The experimental results show that under heavily congested traffic conditions the LBSM can outperform all existing control strategies with respect to the work zone throughput, the average vehicle delay, the average stop delay, and the average number of stops. This study has also investigated critical traffic flow related factors that may impact on the performance of such a system.

Analysis of Work Zone Traffic Behavior for Planning Applications

Understanding work zone traffic behavior is important for the planning and operation of work zones. The objective of this paper is to develop a mathematical model of work zone traffic flow elements by analyzing the relationships between speed, flow, and density that can be used to estimate the capacity of work zones. Traffic flow data were collected from 22 work zone sites on South Carolina interstate highways. The scatter plots of the collected data demonstrate that the relationship between speed and density does not follow Greenshields’ linear model. A non-linear hyperbolic model was developed to describe the relationship between speed and density. Using this model the capacity of a work zone was estimated to be 1550 passenger cars per hour for 2-lane to 1-lane closures. Adjustments to this capacity value to consider other types of vehicle as well as the work zone intensity are provided. Highway agencies can use this estimated capacity along with anticipated traffic demand to schedule work zone operations to avoid long periods of over-saturation. The tapered approach to work zone lane closures used by South Carolina is similar to methods used in work zones throughout the world. The authors believe that the methodology described in this paper for modeling work zone traffic as well as estimating work zone capacity is transferable to other countries. The conversion of actual volumes to passenger car equivalents may have to be modified due to the significant differences in traffic makeup between the United States and other countries.

Development of Traffic Delay Assessment Tool for Short-Term Closures on Urban Freeways

A certain amount of delay in work zones is typically assumed to be unavoidable and often considered a cost of doing business when roadway improvements are in progress. Therefore, developing a method to predict delay, such that appropriate countermeasures to minimize delay can be implemented, is critical to successful work zone management. Predicting work zone delay in an effective and efficient manner should not require extensive data collection or long, complex coding efforts. The procedure should be customizable for local data availability, easy to use, and, for practitioners, easy to interpret. To this end, the Work Zone Capacity Analysis Tool (WZCAT) analytical software program was developed to predict delays and queues for short-term (daily) work zone closures. WZCAT queue-length predictions are based on a simple input-output model, with capacity of the work zone controlling the throughput. The purpose of this study was to evaluate and enhance WZCAT with field data as well as summarize various aspects of traffic flow and queuing patterns during work zone operations on selected urban freeways. Findings from field observations were significant traffic volume changes on exit and entrance terminals upstream of work zones and the stabilization of vehicle queue after initial queue development. A demand-adjust factor was developed and applied to WZCAT-R for effectiveness and efficiency. WZCAT-R produces effective results for queue prediction. It can be an effective and reliable tool in predicting work zone delay and queue development. The tool can also help engineers proactively plan work phasing, lane restrictions, and potential detour routes to move traffic more efficiently.

Dynamic Late Merge Control at Highway Work Zones

The purpose of this study is to present the evaluation result of a dynamic late merge (DLM) system for highway work zone operations, experimented by the Maryland State Highway Administration and International Road Dynamics Inc. The evaluation focuses mainly on the operational efficiency such as the input–output analysis, work zone throughput, volume distribution, and resulting queue length. Evaluation results reveal that a properly deployed DLM system can indeed outperform the conventional merge control with respect to the total work zone throughputs. Such a system, however, may result in excessive traffic conflicts if not properly integrated with existing static warning signs for work zone operations. Some suggestions and guidelines developed from field observations and analysis results for potential improvement of the DLM performance are also presented in this paper.

Dynamic Late Merge Control at Highway Work Zones: Evaluations, Observations, and Suggestions

The purpose of this study is to present the evaluation result of a dynamic late merge (DLM) system for highway work zone operations, experimented by the Maryland State Highway Administration and International Road Dynamics Inc. The evaluation focuses mainly on the operational efficiency such as the input-output analysis, work zone throughput, volume distribution, and resulting queue length. Evaluation results reveal that a properly deployed DLM system can indeed outperform the conventional merge control with respect to the total work zone throughputs. Such a system, however, may result in excessive traffic conflicts if not properly integrated with existing static warning signs for work zone operations. Some suggestions and guidelines developed from field observations and analysis results for potential improvement of the DLM performance are also presented in this paper.

Optimal Dynamic Speed-Limit Control for Highway Work Zone Operations

Despite the well-recognized fact that proper control of traffic speed can contribute to both a reduction in accidents and improved efficiency of highway operations, most existing speed-control strategies implemented in Europe and the United States tend to aim only at improving traffic safety. An on-line algorithm for variable speed-limit control at highway work zones is presented that can take full advantage of its dynamic functions and concurrently achieve the objectives of throughput maximization and accident minimization.