Work Zone Traffic Control Research Articles

Evaluation of Auxiliary Signing for Driveway Assistance Devices at Low-Volume Access Points within One-Lane, Bidirectional Work Zones

Work zone traffic control presents unique challenges during single-lane closures on two-lane, two-way facilities. In these circumstances, traffic regulators (i.e., flaggers or temporary signals) ensure alternating one-way travel in the work zone. However, the use of traffic regulators becomes less practical at mid-segment low-volume access points, such as driveways and minor intersections, within the lane closure. These locations present additional risk for flaggers and, owing to financial infeasibility, are often rendered without traffic control. A recently developed experimental traffic control treatment, the driveway assistance device (DAD), is designed to provide guidance to motorists for a safe entrance into the lane closure from low-volume access points. As this device is relatively new, much is still unknown about the optimal device design and operation to provide the highest compliance. To address this, a field study was performed to evaluate driver compliance associated with DADs implemented at a series of driveways along a one-lane, two-way work zone along a state highway in northern Michigan. As little guidance exists for DAD auxiliary signage, the field study specifically sought to compare the effects of five different sign messages utilized with the DAD. The driver compliance data revealed that the most effective sign messages were those that included “Turn” instead of “Yield,” a prominent “WAIT” message at the top, in addition to a supplemental “No Turn on Red” sign. Based on these findings, DADs are recommended for continued experimental use along with appropriate auxiliary signage at work zones where one-lane, two-way traffic is being maintained.

Development and Evaluation of a MASH TL-3 Modified Single Wood-Post Skid-Mounted Sign Support System

Previous crash testing determined that the conventional Texas Department of Transportation, U.S., single wood-post, skid-mounted temporary sign support system did not satisfy guidelines included in the American Association of State Highway and Transportation Officials Manual for Assessing Safety Hardware (MASH). Modifications were made to the system to improve impact performance and meet MASH requirements. The modifications included increasing the mounting height of the sign, installing weakening holes in the wood support post at a prescribed height, and adding a wire rope loop around the weakening holes to act as a hinge mechanism when sections of the wood sign support fracture during vehicle impact. Crash tests were performed on the modified system in accordance with the MASH Test Level 3 (TL-3) matrix for work-zone traffic control devices. The modified single wood-post, skid-mounted temporary sign support system with a 90 in. sign mounting height, weakening holes, and tether cable met the performance criteria for MASH TL-3 work-zone traffic control devices.

Evaluation of the Impact of Work Zone Traffic Control Devices on Change of Speed Using the SHRP 2 Naturalistic Driving Study

Speeding is a major concern in work zones and a major contributor to work zone crashes. Around 71.4% of fatal work zone crashes are speeding-related compared with 30% of fatal crashes overall. Addressing speeding in work zones is therefore critical to improving work zone safety. This study utilized data from the second Strategic Highway Research Program Naturalistic Driving Study to evaluate the impact of traffic control devices (TCDs) on reducing driver speed in work zones. Time series data assessed changes in speed for 380 drivers over 104 unique work zones on four- or multilane roadways. Speed change was measured for single-point TCDs encountered in the work zones (i.e., signing, changeable message signs [CMSs]), and estimated using a linear mixed-effect model. Results indicated speeds reduced by 4.0 mph for dynamic speed feedback signs (DSFSs), 2.3 mph for speed limit signs (both regular and work zone), 2.2 mph with trailer-mounted- and 1.2 mph for active overhead CMSs, 2.8 mph for arrow boards, and up to 2 mph for other static work zone sign types. Driver characteristics (i.e., age, gender, glance location, cell phone use) were included in initial models but were not statistically significant, probably because of sample size. For instance, simple statics indicated that drivers engaged in a cell phone task had a decrease of only 1 mph when encountering a DSFS whereas drivers not engaged in a cell phone task decreased speed by over 4 mph. However, only seven drivers were engaged in a cell phone task when encountering a DSFS—probably too small to detect statistical significance.

Assessing Work Zone Traffic Control Options for 3-to-1 Lane Closures

The presence of highway construction zones hinders mobility and affects traffic operations. A 2002 study by Wunderlich & Hardesty reported that nearly 20% of the National Highway System roads have scheduled construction work during the peak construction season. Additionally, approximately 24% of non-recurring delays on freeways are caused by work zones. To minimize time lost by travelers due to work zone induced traffic congestion, it is important to efficiently plan temporary traffic control (TTC) at work zones. Earlier research conducted by Sisiopiku & Ramadan, 2017 confirms that the majority of State Departments of Transportation currently rely on their earlier experience when planning for work zones, rather than consider operational and safety impacts. Using a study corridor in Birmingham, Alabama as a test bed, this study investigated the operational impacts of TTC options for work zones with 3-to-1 lane drop configuration using traffic data collected from the Alabama Department of Transportation. The VISSIM simulation platform was used to conduct the experiments. The experimental design considered two TTC strategies (i.e., static late and early merge) under 3-to-1 lane drop configuration for work-space length of 500 ft for long- and short-term lane closures. The study concluded that the 3-to-1 lane-drop configuration should not be scheduled for long-term duration. Maintenance work can be scheduled from midnight to early morning and under the 3-to-1 lane closure scenario the performance of early and late merge traffic control is similar. Overall, this study used simulation modeling to compare the effectiveness of two traffic control strategies at work zones on the basis of different performance measures. The results provide information about the impact of each control strategy on density, speed, travel time etc. They also help determine what time of the day is best for lane closings in order to reduce adverse impacts from capacity reduction. Thus, the findings are expected to provide valuable guidance for agencies responsible for planning, design, and operations of work zones in the future.

Development of Work Zone Traffic Control Algorithm for Two Lane Road

교대통행은 2차로 도로에서 한 차로를 점용한 공사 시, 다른 한 차로를 교대로 사용하여교통류를 처리하는 공사구간 교통관리기법이다. 신호수를 이용한 교대통행 교통관리 방안은 작업자의 안전문제와 방향별 통과 교통수요에 능동적으로 대처하는데 한계가 있다. 이런 잠재적 문제점을 해결하기 위한 하나의 방안으로 이동식 교대통행 운영시스템을 개발ㆍ적용하는 것이다. 본 연구에서는 이 시스템의 교통제어 기법을 개발하였다. 검지기에서 수집되는 방향별 교통량을 이용하여 공사구간 교대통행에 적용 가능한 교통제어 운영변수를 도출하고, 공사구간 내 차량의 존재 유무를 고려한 알고리즘을 설계하였다. 또한 교대통행 제어시스템의 운영효율성 극대화를 위하여 제어변수 최적화를 실시하였다. 최적화방안으로 유전알고리즘 기법을 적용하였으며, 적용 유무에 따른 지체시간을 산출하여 운영효율성을 평가하였다. 그 결과, 최적화를 시행했을 때 총 지체시간과 차량 한 대당 지체시간 모두 감소하는 것으로 나타났다. 본 연구에서 제시한 교대통행 동적제어 알고리즘을 통하여 교대통행 공사구간을 통과하는 차량에게 지체시간 감소효과를 기대할 수 있다.

Evaluation of Merge Control Strategies at Interstate Work Zones under Peak and Off-Peak Traffic Conditions

Maintenance and rehabilitation projects of interstate facilities typically mandate lane closures. Lane closures require merging maneuvers that often result in reduced speeds and traffic bottlenecks. Work zone impacts on traffic operations are magnified when project durations are extended. Conventionally, work zone traffic control plans are developed to address work zone impacts. This study evaluated various merge control strategies at interstate work zones peak and off-peak traffic conditions and summarized related impacts. A comprehensive microscopic simulation model was developed in full consideration of driver/vehicle behavior at work zones. The analysis of simulation results revealed that merge control strategies, when implemented during peak and off-peak conditions, can preserve the level of service and provide favorable mobility, safety, and environmental impacts. In addition, results indicate that transportation agencies’ practice of scheduling work zone activities during the off-peak may not be the most optimum approach. Overall, the findings of this study highlight the need for evaluation of work zone scheduling practices in full consideration of agency, user, and project costs.

Exploring endogeneity of macroscopic speed parameters: empirical study during low volume conditions in construction work zones

This paper uses a simultaneous equation modeling approach to explore the relationships between mean speed, standard deviation of speed and work zone design characteristics. Data for model estimation were collected in 17 work zones on four-lane, divided freeways in Pennsylvania and Texas. The three-stage least squares estimator was used, as it is both consistent and efficient in the presence of endogeneity and error covariance. The fixed effects and random effects estimators with instrumental variables were also used to address possible unobserved heterogeneity. Results pointed towards a truly simultaneous structure, where mean speed is determined by exogenous design and traffic control features and the standard deviation of speed and the standard deviation of speed is dependent on design and traffic control features as well as mean speed. A number of work zone design and traffic control features directly influenced both speed parameters. Findings of this research indicate the relationship between speed magnitude, speed dispersion and work zone design and traffic control features is more complex than documented generalizations made in current work zone design and traffic control decision processes.

Automated traffic light system for road user's safety in two lane road construction sites

The road construction safety traffic light system is designed to replace a manual traffic control on a road construction sites. This device can replace one or both flaggers during the two lane closures on the event of a road construction. The road construction safety traffic light system is considered one of the best devices in work zone traffic flow control systems. The device is a portable traffic light unit which can be best utilized in controlling traffic flow in a road construction site for long term or short term lane closures and to control two-way traffic in a single lane. By implementating new technologies in automating traffic flow in road construction site could possibly eliminate the usage of a conventional flagman at all times. The road construction safety traffic light system is a practical solution to solve problems which contribute towards hazards at road construction site and to be inline with the road safety regulation which is taken into granted by the contractors. The automated portable traffic light system can reduce direct costs in man power utilization and increase safety for the road users and construction workers by eliminating the need for a human flagmen. This system is applicable for public and privately funded road construction projects that require overnight or 24-hour traffic control as well as in different weather conditions.

Statistical comparisons of the crash characteristics on highways between construction time and non-construction time

Many studies in the past reported that crash frequencies during construction time were higher than during non-construction time at the same highway sections. A question was raised whether this trend applies to work zones in Utah. Descriptive statistics (mean, standard deviation and histogram), a paired t-test, a two-way ANOVA, and a Tukey test were used to test whether the crash rates are statistically higher during construction time than during non-construction time at the same highway sections using 202 work zone sites located on Utah's highways. These highway sections were grouped into four highway classes and the crashes were grouped into six crash severity levels. It was found that the difference in mean crash rates between construction time and non-construction time was not statistically significant at the 95% confidence level, indicating that the trend of higher crash rates during construction time reported by previous work zone safety-related studies was statistically not supported by Utah's work zone crash records. The observance by contractors of Utah Department of Transportation's (UDOT's) guidelines for work zone traffic control may have helped them achieve a similar level of traffic safety during construction and non-construction times.

Seemingly Unrelated Regression Model of Car Speeds and Speed Deviations in Freeway Work Zones

Current work zone design and traffic control guidance is based heavily on desirable speed-related outcomes, but knowledge concerning actual speed-related outcomes of design and traffic control decisions is limited. The objective of this research is to investigate relationships between speed behavior, roadway and roadside geometrics, and traffic control in work zones. The objective is accomplished through specification and estimation of a seemingly unrelated regression (SUR) model. The dependent variables modeled were 85th-percentile passenger car speed and standard deviation of passenger car speed. Work zone design and traffic control features were investigated as explanatory variables. Speed and infrastructure data used for estimation were collected in Pennsylvania and Texas work zones. The SUR model accounted for contemporaneous correlations of the disturbance terms in the two speed equations. In the equation for 85th-percentile speed, regression parameters were statistically significant for variables representing work zone configuration, type of roadway infrastructure, work zone location, distance traveled from the beginning of the work zone, posted speed limit, vertical alignment, and total paved cross-section width. In the equation for standard deviation of speed, parameters were statistically significant for variables representing distance traveled from the beginning of the work zone, total paved cross-section width, and reduction in posted speed and roadside conditions. Several recommendations for future work are provided, including expansion of the system of equations to include 85th-percentile truck speeds and standard deviation of truck speeds and consideration of possible contemporaneous relationships between speed measures.

Part 2: Work Zone Traffic Control and Safety: Motorist Comprehension of Traffic Control Devices for Mobile Operations

In 2004, researchers conducted surveys to evaluate motorist comprehension of various mobile traffic control devices used to inform drivers about the number of vehicles in a work convoy; speed differential between the work convoy and the normal traffic stream; and passing a work convoy on two-lane, two-way roadways with improved shoulders. Four static signs were investigated to ascertain whether they inform motorists that they are approaching multiple work vehicles. Three of the signs (including the sign Work Convoy) had comprehension levels less than 53%. Placing the number of work vehicles on the sign (i.e., 3 Vehicle Convey) improved the comprehension level to 79%. Various mobile speed displays were evaluated to determine if they provide information to motorists about the speed differential between the work convoy and approaching traffic. Only the Your Speed display (indicating speed of approaching vehicles) was understood by more than 85% of participants. In Texas, when mobile operations are cond...

Part 2: Work Zone Traffic Control: Field Evaluation of Late Merge Traffic Control in Work Zones

The traffic control strategy of the late merge in work zones was devised to improve flow and safety at work zone lane closures. Although some states have put the strategy into practice, only a handful of short-term field studies have formally evaluated its effectiveness. Additional field studies were necessary to assess the efficacy of the strategy and its proper deployment. This paper documents the results of a field test of the late merge traffic control conducted over several months. The late merge strategy was evaluated by comparing its effectiveness with that of traditional plans for work zone lane closures. The field test was conducted on a primary route in Tappahannock, Virginia, at a two-to-one lane closure. Results showed that throughput increased, but the increase was not statistically significant. Likewise, time in queue decreased, but the decrease was not statistically significant. These results were much less dramatic than those of other studies. Possible reasons for this disparity include different driver populations, road types, vehicle mixes, and site-specific characteristics. Despite limited improvements in throughput and time in queue, more drivers were in the closed lane, a positive response to the late merge signs.

Determining Design Wind Loads for Work Zone Traffic-Control Devices

Proper traffic control and delineation are critical to achieving safety in work zones. In addition to being crashworthy, a barricade or temporary sign support should have the ability to withstand anticipated service loads. If a barricade or temporary sign support fails or overturns, it cannot perform its intended function and the safety of the work zone may be compromised. Currently, no guidance is provided on the service loads that should be used in the design of these work zone devices. Recommendations are provided for design wind loads for work zone traffic-control devices. The results from field trials indicate that truck-induced wind loading is not a critical design issue for barricades and barricades with signs. The recommendations are thus based on an analytical determination of design wind speeds associated with different recurrence intervals that correspond to the duration of work zone activities. Analytical case studies are presented for two common barricade designs, with consideration given to both structural capacity and overturn. Guidance on the amount of ballast required to prevent overturn is provided as a function of wind speed, barricade length, and sign mounting height.

Evaluation of Automated Work Zone Information Systems

Motorists traveling through work zones are faced with both routine and unexpected tasks of driving coupled with additional distractions provided by the work zone. This can create conflicts despite significant applications of work zone traffic-control devices. When one or more through-traffic lanes are closed and traffic volumes exceed the capacity of merge points or of the reduced number of lanes, congestion can lead to the formation of queues, which result in delays and increased potential for crashes. An automated work zone information system (AWIS) may be implemented at a work zone to notify approaching motorists of changing traffic conditions, such as slowdowns or backups. Research was conducted at rural work zones in Arkansas on I-40, where two lanes of traffic in a direction were reduced to one lane. The objectives were to compare the displays of an AWIS with field observations of traffic conditions and to determine at what volume backups were forming. AWIS was compared with field observations for two traffic speeds, 30 and 50 mph. At 30 mph, the speed at which the system was programmed to identify a backup, AWIS concurred with the field observations 92% of the time. For a perceived backup speed of 50 mph, the system indicated a backup about 88% of the time. Backups formed at short-term flow rates as low as 800 to 900 passenger car equivalents per hour, which is lower than the capacities reported in the literature (1,100 to over 2,000 vehicles per hour).

Radial Basis Function Neural Network for Work Zone Capacity and Queue Estimation

An adaptive computational model is presented for estimating the work zone capacity and queue length and delay, taking into account the following factors: number of lanes, number of open lanes, work zone layout, length, lane width, percentage trucks, grade, speed, work intensity, darkness factor, and proximity of ramps. The model integrates judiciously the mathematical rigor of traffic flow theory with the adaptability of neural network analysis. A radial-basis function neural network model is developed to learn the mapping from quantifiable and nonquantifiable factors describing the work zone traffic control problem to the associated work zone capacity. This model exhibits good generalization properties from a small set of training data, a specially attractive feature for estimating the work zone capacity where only limited data is available. Queue delays and lengths are computed using a deterministic traffic flow model based on the estimated work zone capacity. The result of this research is being used to develop an intelligent decision support system to help work zone engineers perform scenario analysis and create traffic management plans consistently, reliably, and efficiently.

CBR Model for Freeway Work Zone Traffic Management

A case-based reasoning (CBR) model is presented for freeway work zone traffic management. The model considers work zone layout, traffic demand, work characteristics, traffic control measures, and mobility impacts. A four-set case base schema or domain theory is developed to represent the cases based on the aforementioned characteristics of the problem. It includes a general information set, a problem description set, a solution (or control) description set, and an effects set. To improve the interactivity of the CBR system and its user-friendliness, a hierarchical object-oriented case model is developed for work zone traffic management. The model is implemented into an intelligent decision-support tool to assist traffic agencies in the development of work zone traffic control plans and to better design and manage work zones for increased mobility and safety. Three examples are presented to show the practical utility of the CBR system for work zone traffic management.

Crash Testing and Analysis of Work-Zone Sign Supports

A variety of traffic-controlling devices are used in work zones; some of these are not normally found on the roadside or in the traveled way outside of the work zones. These devices are used to enhance the safety of the work zones by controlling the traffic through these areas. Because of the placement of the traffic control devices, the devices themselves may be potentially hazardous to both workers and errant vehicles. The impact performance of many work-zone traffic control devices is mainly unknown, and to date limited crash testing has been conducted under the criteria of NCHRP Report 350: Recommended Procedures for the Safety Performance Evaluation of Highway Features. The results of full-scale crash testing of flexible panel work-zone sign stands were evaluated and analyzed to quantify the features that successful devices shared, as well as common features of those devices that failed salient safety criteria. Parameters considered included sign base and upright properties, sign height, cross-member properties, and ancillary details. Results pointed to three problematic, fundamental design issues: ( a) combinations of base and upright stiffness and strength that generally lead to significant windshield damage, ( b) cross members that lead to windshield damage in the end-on (90°) impact orientation, and ( c) appurtenances that have an impact on performance. Although there are a significant number of variables that control the performance of a given device, these generalizations offer a basis for the evaluation of the fundamental design elements.

Quality Assurance Program for Work-Zone Traffic Control

A quality assurance program was developed and implemented by the New York State Department of Transportation to manage work-zone traffic control on department projects. Using a standardized process, a team of experienced engineers inspects a large sample of projects across the state each year. Standard rating forms are completed to describe the temporary traffic control observed on each project. “Emphasis points,” which describe recurring areas of concern, are evaluated on each project, and a quality rating is assigned using a standardized six-point 0 to 5 scale to describe the overall condition and effectiveness of the project. Quality goals have been established both for average ratings for regional program areas and for individual projects. Implementation of this quality assurance program over the past 14 years has led to a substantial improvement in the quality of work-zone traffic control on New York State projects.

Evaluation of Speed Displays and Rumble Strips at Rural-Maintenance Work Zones

An evaluation of the effectiveness of speed displays and portable rumble strips at reducing speeds in rural-maintenance work zones is described. Speed displays are radar-activated signs that dynamically display approaching vehicle speeds. The devices were tested on two-lane low-volume, high-speed rural roads where maintenance activities were completed in a single day. Speed and volume data were collected for cars and trucks as they traveled through four work zones. These data were collected when no work-zone traffic control was present, when normal work-zone traffic control was set up, and when the test treatment was installed. The results for the portable rumble strips were mixed, with passenger cars experiencing less than a 3.2-km/h (2-mph) reduction in mean speed approaching the temporary traffic-control zone. The impact of the rumble strips on trucks was more pronounced, with mean speed reductions approaching the temporary traffic-control zone of up to 11.6 km/h (7.2 mph) lower than normal traffic control. The percent of vehicles exceeding the speed limit in the advance warning area was also reduced when the rumble strips were used. The speed display was generally more effective than the rumble strips at reducing speeds in the advance warning area. Mean speeds were often reduced approaching the activity area, with speed reductions of up to 16.1 km/h (10 mph) being achieved. The percentage of vehicles exceeding the speed limit was also reduced in the advance warning area.

Work Zone Traffic Accidents Involving Traffic Control Devices, Safety Features, and Construction Operations

There were 496 work zone traffic accidents on New York State Department of Transportation construction projects from 1994 through 1996. These accidents involved impacts with work zone traffic control devices and safety features; construction features, such as pavement bumps and joints; drainage features; excavations and materials; and construction vehicles, equipment, and workers. These items, which include all of the features introduced into the roadway environment by construction activity, represent one-third of all work zone accidents and 37 percent of those involving serious injury. Channelizing devices, arrow panels, signs, and other traffic control devices generally resulted in little harm when impacted. Impact attenuators, both fixed and truck mounted, also performed well. Although portable concrete barriers prevent vehicle intrusions, impacts with barrier are severe events. Barriers must be properly designed and limited to only those locations where they are needed to protect more serious hazards. Construction vehicles, equipment, and workers were involved in over 20 percent of all work zone accidents, resulting in serious injuries. Although intrusions by private vehicles into work spaces are a serious concern, construction vehicles, equipment, and workers in open travel lanes are also a serious concern. Good design of work zone traffic control plans, combined with adequate training and supervision of workers, is essential to control both concerns.