Guidelines for Using Late Merge Traffic Control in Work Zones

Typical traffic control and operations at work zones are not effective in mitigating the work zone bottleneck, as the common early merge behavior limits utilizing the available capacity in the closed lane. Recently, using late merge strategy is encouraged to fully utilize the closed lane, therefore increasing efficiency of the work zone. In practice, the late merge strategy does not work effectively due to the lack of compliance by drivers. This paper is aimed at exploring two work zone late merge strategies with and without enabling connected vehicles (CV) technology. This first strategy is the late merge without CV enabled. The second strategy incorporates CV-enabled cooperative merge to enhance the work zone efficiency through communications between vehicles in the open and closed lanes. The CV-enabled strategy employs a rule based decentralized control algorithm. The paper has implemented both late merge strategies in microsimulation and evaluated the operational performances. Three major performance measures, which are throughput, delay and queue length, are used in the evaluation. The results indicate that the operational performance of the CV-enabled cooperative late merge is superior to the late merge strategy without CV in most cases, especially when traffic demand is moderate, while both late merge strategies outperform the traditional early merge strategy. Moreover, effects of the control variables including the traffic demand, heavy vehicle percentage, lane distribution percentage, late merge length, reduction of gap acceptance factor, and compliance rate, have been analyzed. Ultimately, sensitivity analysis has been performed to investigate the trend of effects from the significant variables control.

Conventional traffic control plans for lane closures of rural Interstate highways normally work well as long as congestion does not develop. However, when the traffic demand exceeds the capacity of the work zone, queues may extend back past the advance warning signs, often surprising approaching traffic and increasing the accident potential. Also, smooth and orderly merging operations may be lost as some drivers remain in the closed lane attempting to squeeze into the open lane at the head of the queue, while other drivers try to prevent drivers in the closed lane from passing them by straddling the centerline or traveling slowly in tandem with another vehicle in the closed lane. These maneuvers tend to reduce the capacity of the merging operation and increase the accident potential and road rage among drivers. Early merge and late merge are two forms of merge control designed to deal with these problems. However, these approaches have operational characteristics that limit their effectiveness under both congested and uncongested traffic flow conditions. The advantages and disadvantages of each approach are examined. A new concept called the dynamic late merge is described, which features the integration of the late merge and conventional lane-closure merge control on the basis of real-time measurements of traffic conditions in advance of the lane closure.

A series of field evaluations were conducted within work zone lane closures on rural freeways in Michigan to determine 1) the optimal positioning of a speed feedback trailer (SFT) approaching an active work area, 2) the effectiveness of a digital speed limit (DSL) sign for posting work zone speed limit reductions, and 3) the effectiveness of a speed feedback panel paired with a DSL. Speed trajectories were collected for vehicles traversing each work zone using a series of handheld light detection and ranging (LiDAR) guns operated by a team of technicians seated in unmarked vehicles within each lane closure. The SFT was found to be increasingly more effective at reducing speeds of vehicles approaching and entering the work area as it was positioned closer to the work area. Positioning the SFT 200 ft from the start of the work area, which was determined to be the optimal position, reduced speeds entering the work area by 3.1 mph compared with when the SFT was positioned further upstream. This SFT position helps ensure that motorists receive timely feedback within sight of the work area while providing sufficient deceleration time to maximize speed reductions as drivers enter the work area. The use of a DSL to reduce the work zone speed limit from 60 mph to 45 mph reduced vehicle speeds by 3.7 mph near DSL. Furthermore, activation of the speed feedback panel that was on the same assembly as the DSL reduced vehicle speeds by an additional 1.8 mph.

Research performed to assess the effectiveness of a flashing warning-light system for use at work-zone lane closures is summarized. The system is composed of a series of interconnected, synchronized flashing warning lights that produce the illusion of motion. Researchers investigated motorist understanding and perceived usefulness of various designs of the warning-light system, and the potential of this system to yield significant operational or safety benefits in actual work-zone applications. Results from proving ground and field studies show that the flashing warning-light system used in the work-zone lane closure is perceived positively and is not confusing to the motoring public. The field-study results also revealed that the prototype warning-light system may encourage motorists to vacate a closed travel lane farther upstream from the work zone (which is believed to offer a potential safety benefit). When the warning-light system was activated at the urban freeway test site, a relatively new closure, there was a one-fourth reduction in the number of passenger vehicles and a two-thirds reduction in the number of trucks in the closed lane 305 m (1,000 ft) upstream of the lane closure. However, the system did not significantly affect lane choice at the rural road test site where the lane closure had been installed for 6 months. Thus, the greatest potential safety benefit of the warning-light system may be when it is used in conjunction with short-duration or intermediate-term maintenance or construction projects.

Estimation of the capacity of work zones is vital to manage the possibility of traffic flows exceeding capacity and resulting in unbearable queues during work zone lane closures. A plethora of research papers have studied several ways to estimate work zone capacity, with the Highway Capacity Manual (HCM) having its own methodology to estimate capacity based on various site characteristics. However, HCM always recommends validating its model with local data to reflect the actual driving behavior of the region. This study considered work zone capacity as a function of queue discharge rate (QDR), defined as the 15-min average flow rate immediately after breakdown, also known as postbreakdown flow rate. By collecting data from 10 different work zones within the state of Louisiana, the study estimated QDR and its corresponding duration at breakdowns. An average QDR of 1,664 pcphpl and an associated queue of 120 min average duration was found. Analysis of variance showed that average QDRs across all sites were not significantly different. The QDR prediction model revealed that a closed right lane and a work zone on linear roadways significantly increased the discharge rate. However, the presence of nearby exit ramps, daytime scenarios, and an increase in the speed ratio and truck percentages were found to decrease the discharge rate. A separate model for the duration of queue or breakdown found the time of day, change in the speed ratio, presence of entry ramp, location of work zones, and annual average daily traffic of the roadway to be significant variables.

The reduction of upstream end-of-queue (EOQ) crashes at work zone lane closures has been a focus of the Texas Department of Transportation, Austin, for several years. An ongoing widening effort on Interstate 35 through central Texas prompted officials to examine and implement technologies to mitigate the impacts of EOQ warning crashes. An EOQ warning system was established, which consisted of a highly portable work zone intelligent transportation system of easily deployable radar speed sensors linked to one or more portable changeable message signs and highly portable transverse rumble strips. The EOQ system was deployed upstream of nighttime lane closures, where queues were expected to develop. Although the sample sizes were relatively small, the trends did suggest that the systems were having a positive effect to reduce crashes. Overall, the EOQ warning system was estimated to have reduced crashes 44% from what they otherwise would have been if the system had not been used. The crashes that did occur were less severe, which was most likely because fewer of them were of the high-speed, rear-end-collision variety. With traditional societal crash cost values updated to 2014 dollars, the use of the EOQ warning system at nighttime lane closures reduced crash costs by $1.36 million over the analysis period. This figure equated to $6,313 in crash cost savings per night of deployment. Compared with the approximate costs of procurement and deployment of these systems, a break-even point was achieved after 95 to 190 nights of use.

The study proposes the association between work zone types and work zone lane closure types used in the construction of South Korean expressways through the use of the text mining and association analysis techniques. Of the factors that greatly affect the capacity of work zones, work zone lane closure types and night work were analyzed. Words were extracted from the narrated work types using the text mining technique, and the associations among the words, lane closure types, and night work variables were identified. The analysis revealed a significant difference between the work types associated with main lane closure and shoulder lane closure. It is expected that this study can be effectively applied to establishing transportation management plans (TMPs) for work zones.

The impact of work zones on mean travel time and travel time reliability has gained attention as agencies focus on performance measurement. Travel time reliability in work zones often has been difficult for agencies to quantify because of the time and expense required to collect travel time data. Several private-sector companies have begun to sell travel time data; this availability has created an opportunity to examine cost-effectively work zone impacts on travel time reliability on a broader basis. The Virginia Department of Transportation recently acquired probe vehicle-based travel time data for 2010 from a private-sector data provider. These data were used to calculate measures of travel time reliability at 15 work zones and to examine factors that affected travel time reliability. Travel time reliability was quantified with 95th percentile travel time, a buffer index, and a planning time index. The work zones experienced a statistically significant degradation across all measures of travel time reliability as compared with baseline conditions. Work zone mean buffer index, planning time index, and 95th percentile travel time rates were higher by 48%, 18%, and 16%, respectively. Although lane closures occurred during off-peak periods, work zones that involved lane closures experienced increases in their mean buffer index, planning time index, and 95th percentile travel time with rates of 67%, 23%, and 22%, respectively. Annual average daily traffic per lane and the number of access points per mile were found to have the most obvious relationships with declines in reliability at work zones.

The paper provides methodologies for microscopic simulation modelling of freeway work zones with lane closures in the proximity of interchanges. In addition, the research presents simulation results using calibrated modelling parameters to determine the capacity available for mainline flow under various operating conditions. The results will help researchers or practitioners with designing and studying freeway work zone sites under various lane configurations using better estimates of delays and queue sizes in the proximity of interchanges. Additionally, a 2 to 1 on-ramp merge condition was explored to predict the merge ratios under both demand and service flow conditions. The paper illustrates how ramp demand affects the share of segment capacity available to mainline traffic to reveal strategies for controlling this demand (via ramp metering for example) in order to maintain a prescribed freeway capacity through the work zone. The overall study result indicates the degree to which the presence of a work zone with lane closures decreases the proportion of mainline flow and shows the degree to which differences in work zone lane configurations affect merge and weave scenarios.

The traffic congestion problem in urban areas is worsening since traditional traffic signal control systems cannot provide efficient traffic control. Therefore, dynamic traffic signal control in intelligent transportation system (ITS) recently has received increasing attention. This study devised an adaptive and cooperative multi-agent fuzzy system for a decentralized traffic signal control. To achieve this goal we have worked on a model, which has three levels of control. Every intersection is controlled by its own traffic situation, its neighboring intersections recommendations and a knowledge base, which provides the traffic pattern of each intersection in any particular day of the week and hour of the day. The proposed architecture comprises a knowledge base, prediction module and a traffic observer that provide data to real traffic data preparation module, then a decision-making layer takes decision to how long should the intersection green light be extended. The proposed architecture can achieve dynamic traffic signal control. We have also developed a NetLogo-based traffic simulator to serve as the agents' world. Our approach is tested with traffic control of a large connected junction and the result obtained is promising; The average delay time can be reduced by 21.76% compared to the conventional fixed sequence traffic signal and 14.77% compared to the vehicle actuated traffic signal control strategy.

Research conducted to explore the effects of natural diversion on traffic conditions and travel patterns upstream of temporary work zone lane closures on high-volume urban freeways in Texas is described. Specific objectives were to explore how natural diversion affects traffic volumes at the exit and entrance ramps upstream of the lane closures and the interrelationships between the freeway and frontage road operating conditions that develop at a closure and the amount of natural diversion that occurs. The field studies showed that the rate of queue growth upstream of the short-term lane closures diminished significantly after the first hour at each site. Eventually, the queues approached a balanced state in which the upstream end of the queue became almost stationary. This stabilization was due to significant reductions in entrance ramp volumes both upstream of the freeway queue and within the limits of queuing, as well as to changes in exit ramp volumes within the queue. As a result of these ramp volume changes the constrained flow rate within the queue increased as a function of the distance upstream of the actual lane closure. Using the theory of shock waves in a traffic stream it was shown that the changes in ramp volumes and resulting impact on constrained freeway flow rates within the queue were consistent with the queue stabilization process observed at each site.

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.

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 study explored the impact of in-vehicle messages relative to roadside messages to alert drivers to events within a simulated work zone, in order to determine if these messages can improve driving performance within the work zone. Safety risks in work zones are usually mitigated by design standards and clear signage to communicate work zone information to drivers. Due to distraction and other driving task demands, these signs are not always noticed by motorists, nor are they always followed when they are noticed. The driving simulation tested drivers in two different types of work zones, shoulder work, and lane closure. Participants drove through these work zones three times, each with different messaging interfaces to communicate hazardous events to the driver. The interfaces included a roadside, portable changeable message sign, a smartphone presenting only auditory messages, and a smartphone presenting audio-visual messages. There was significantly better driving performance on key metrics including lane deviation for the in-vehicle message conditions relative to the roadside signs. Furthermore, drivers directed visual attention toward the roadway for the in-vehicle message conditions relative to the roadside sign condition. The results indicate that in-vehicle messaging could provide benefits to primary task performance in driving if the message content is appropriately designed. The findings provide support for a design framework to support in-vehicle communication to drivers approaching work zones and other environments to safely alert them to hazards.

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.