Using speed and volume data, the joint merge traffic control plan was found to increase the efficiency of the closed lane and better encourage the use of both lanes... Merged Lane Closed
INTRODUCTION
Problem Statement
The current MUTCD-specified lane closure design aims to guide drivers from the closed lane to the merged lane but can be unsafe and inefficient during high traffic volumes High vehicle concentration in the open lane creates lane volume imbalances, leading to longer queues and varying operating speeds, which are associated with increased crash risks Driver behavior also impacts safety, as some aggressive drivers exploit these conditions by passing slower traffic and merging at the front of the queue, causing irritation among early mergers who wait patiently for their turn.
Blocking lanes, either partially or fully, to prevent late-merging drivers from passing is a common but dangerous behavior Truck drivers often create "rolling blockades" by traveling side by side at the same speed, further impeding traffic flow (Pesti et al., 1999) Such practices have historically led to reckless maneuvers like driving on shoulders, increased road rage incidents, and, in some cases, fatal traffic crashes (Massachusetts Highway Department, 2006).
Extensive research highlights ongoing efforts to improve vehicle safety and mobility in work zones (U.S Department of Transportation, 2002) However, the potential of optimizing the geometric layout of transition zones to address merging challenges has been underexplored Enhancing design features such as taper lengths, alignment of channeling devices, and implementing effective traffic control measures like experimental signs can significantly improve traffic flow and safety at work zone entrances.
Tasks
The primary aim of the study was to evaluate an innovative merge design intended to improve the merging efficiency of two traffic streams into a single lane The research focused on testing whether this experimental approach could enhance traffic flow and safety at merging points Key tasks included analyzing the effectiveness of the new merge design through experimental testing and assessing its impact on traffic congestion and collision rates Overall, the study aimed to determine if the proposed merge system offers a better solution for traffic management and lane merging efficiency.
1 Identify and document both the state-of-the-art and state-of-the-practice with respect to the geometric design and traffic control at the entrance to construction work zones on rural freeways
2 Select or design a merging strategy that was thought to accomplish a more efficient merge than current designs
3 Identify potential sites on rural freeways in Louisiana to test and compare the conventional and experimental merge configuration
4 Generate alternative traffic control schemes for the selected experimental merge design, and apply them to the appointed work zone test site
5 Obtain lane specific speed and volume data from the work zone site
6 Evaluate and analyze the traffic data gathered for the two design configurations, the experimental and the conventionally used configuration
8 Provide recommendations on design features that are thought to enhance the function of the experimental merge configuration.
Significance of Research
The increasing demand for roadway rehabilitation and reconstruction, along with rising traffic congestion, presents significant safety and mobility challenges in work zones across the nation Since 2004, the Federal Highway Administration (FHWA) has mandated that state and local governments receiving federal aid implement measures to improve safety and mobility in work zones Recent statistics highlight ongoing safety and mobility issues in work zones, emphasizing the need for continued research and effective solutions.
A unique and innovative "joint merge" technique was developed to enhance traffic flow and minimize driver frustration near transition zones This method encourages approaching drivers to evenly distribute their lane positions upstream without signaling which lane will end, promoting a fair and balanced merging process Consequently, neither lane has priority, fostering an alternating merge pattern that improves safety and efficiency in transitional roadway areas.
9 lanes simultaneously converge into a single center lane It has been suggested that the joint merge operation can improve traffic operations by:
• reducing queue lengths upstream of the merge point as both the closed and open lanes become evenly utilized;
Enhancing the quality of merging events and promoting a smoother traffic flow within the transition zone are essential for improving overall roadway safety and efficiency This can be achieved by encouraging more uniform operating speeds among drivers and reducing lane changing and weaving behaviors prior to entering the transition zone Implementing these strategies helps create a seamless transition, minimizes congestion, and decreases the risk of accidents, ultimately leading to safer and more efficient traffic management.
• improving driver satisfaction as drivers can no longer gain an advantage by choosing one lane over the other and confusion of which lane is closed is decrease
Despite longstanding global practice of various joint merge strategies, the belief that lane priority must be established during lane closures persists in the United States Limited implementations of joint merge concepts are used in the U.S to promote orderly traffic flow, but until now, this design has not been tested in real-world work zone conditions The findings from this study’s field tests could provide valuable insights for practitioners seeking alternative methods to enhance mobility and safety in work zones As infrastructure age and maintenance increases across the U.S., the adoption of joint merge designs is expected to grow, offering a promising solution for efficient lane management.
LITERATURE REVIEW
Work Zone Traffic Control Issue
High speeds combined with crowded freeways pose a significant safety concern for state highway officials, as dense traffic leaves limited room for driver correction and increases the risk of crashes Crash rates are notably higher in work zones compared to outside areas, with construction reducing roadway efficiency and increasing the likelihood of rear-end collisions Specifically, in Washington State, 35% of freeway crashes are rear-end collisions, often caused by approaching vehicles' inability to stop or maneuver around stationary queues, highlighting the critical safety challenges on busy, congested roads.
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11 transportation operation strategies, and public information strategies (Federal Highway Administration 2006)
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1 High potential for rear end crashes;
2 Drivers not knowing which lane is closed in advance of the queue;
3 Frustrations experienced by drivers in the open lane because drivers in the closed lane are passing them; and
4 Frustration experienced by drivers in the closed lane who are blocked by vehicles straddling two lanes preventing passing
Suggestions were also made by the focus group to address these problems These included practices to:
1 Always close the right lane;
2 Use variable message signs that provide real time information to drivers upstream;
3 Use speed monitoring displays to discourage speeding; and
4 Use no passing zones in advance of the lane closure
Other state agencies such as the Massachusetts Highway Department have been addressing the following notable concerns of work zone management plan:
1 The safety of bicyclist pedestrians, and motorist traveling through the work zone
2 Protection of work crews from hazards associated with moving vehicles
4 Access and maintenance to nearby facilities
5 Issues that may result in project delay
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Work Zone Capacity
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Table 2: HCM Measured Average Capacity for Lane Closures
(Source: Beacher, Fontaine and Garber 2004)
The disparity in capacity estimates often results from the differing methods used to determine capacity Al-Kaisy et al (2000) highlight that maximum flow rates are achieved under specific conditions, emphasizing the importance of accurate measurement techniques for reliable capacity assessment.
A 14 percent decline in speed is typically identified by analyzing speed and time graphs to locate periods where the average speed drops significantly, prior to a sharp decrease Jiang (1999) defines capacity as the traffic flow rate just before a sudden speed drop followed by sustained low vehicle speeds and fluctuating traffic flow, emphasizing that capacity is primarily governed by conditions during congestion rather than free-flow periods This perspective is supported by other studies such as Migletz et al (1999) and Kim, Wang, and Ulfarsson (2007) Additionally, Dixon et al (1996) found that capacity within work zones is affected by the location and intensity of ongoing work activities, with heavy work zones involving significant equipment and personnel resulting in reduced capacity compared to inactive work zones.
Number of Studies Average Capacity (vphpl)
Traffic capacity is primarily influenced by taper designs and upstream merging behaviors Introducing a construction zone on a main freeway reduces overall capacity, leading to a higher likelihood of congestion Effective management of merge zones and taper configurations is essential to minimize congestion impacts and maintain optimal traffic flow.
The Components of a Merging Maneuver
When a roadway is temporarily altered, it is standard practice to install warning signs to inform drivers of the change Conventional traffic control plans typically utilize static signs placed in advance of lane reductions to ensure driver awareness and safety These plans usually feature two warning signs: an initial textual warning sign followed by a second symbolic warning sign, as illustrated in Figures 4 and 5 Such signage effectively communicates upcoming road changes, helping to maintain smooth traffic flow and prevent accidents.
According to Louisiana State Highway Patrol officers, drivers in the closed lane are responsible for safely merging with the open lane, which has priority This merging law is standard across neighboring states and nationwide, promoting early merging in the transition zone Over 95% of drivers in the closed lane complete their merge before reaching the transition zone, with less than 5% utilizing the taper within the zone to merge Implementing priority and encouraging early merging improve traffic flow and safety on highways.
In 1988, it was observed that this phenomenon decreases roadway capacity because available space is underutilized According to McCoy and Pesti (2001), effective lane distribution is a key indicator of merging area efficiency Traffic flow reaches its maximum when vehicles are evenly distributed across lanes, optimizing overall traffic movement.
Research by Zhu and Saccomanno (2003) demonstrated that the direction of a merge significantly impacts driver behavior, with left lane closures producing higher speed variances and uncomfortable deceleration rates exceeding 9.8 ft/sec Their findings indicate that left-to-right merges are more uncomfortable and pose greater safety risks for drivers compared to right-to-left merges, highlighting the influence of merge direction on driver comfort and safety.
Trucks are significantly influenced by the direction of a merge, often remaining in their current lane during congestion, particularly when in the right lane Merging from right to left is generally easier for trucks than from left to right due to larger blind spots on the right side, which can affect safety and maneuverability (Pesti et al., 1999).
Merging Strategies
The conventional merge layout, as shown in Figure 3, includes lane closure signs positioned one and a half miles before the transition zone, followed by a lane reduction sign approximately 1,500 feet from the transition entrance and a flashing arrow panel at the entrance, aligning with MUTCD guidelines However, this design can be inefficient during peak congestion periods, leading to long queues that extend upstream beyond advance warning signs When drivers are unaware of downstream stopped queues, they may fail to stop in time, posing safety risks To address these issues, alternative merging strategies have been explored to improve safety and traffic flow in work zones.
Early merge strategies in work zones, first implemented by the Indiana Department of Transportation, aim to improve driver response times by placing warning signs one mile in advance of lane closures, alerting drivers about upcoming merges According to McCoy and Pesti’s (2001) literature review, some studies indicate that early merge signs can reduce rear-end crashes and forced merges, while others suggest they may increase travel time and the risk of side-swipe crashes The conflicting findings are believed to result from variations in traffic characteristics at different study sites.
The dynamic early merge strategy is based on real-time traffic measurements that activate “Do Not Pass When Flashing” signs upstream of lane closures, as depicted in Figure 7 These signs are positioned at ¼ to ½ mile intervals and work alongside sonic detectors that identify stopped vehicles near the signs When a vehicle is detected, a signal activates the beacon lights on the nearest upstream sign, which turn off once the queue clears While McCoy and Pesti (2001) found that this strategy facilitated smoother merging in a 1997 Indiana Department of Transportation study, it did not increase throughput, and Purdue University simulations indicated that travel times were longer compared to static early merge methods.
Figure 6: Dynamic Early Merge (Source: McCoy and Pesti, 2001)
The “late merge” strategy, developed by the Pennsylvania Department of Transportation, aims to reduce aggressive driving and improve traffic flow by encouraging motorists to utilize both the closed and open lanes up to a designated merging point This method promotes using both lanes until the taper, where vehicles merge in an alternating pattern, reducing bottlenecks and wait times Clear signage is essential; a “Use Both Lanes To Merge Point” sign is typically placed approximately 1.5 miles before the taper, followed by a series of road work signs and a “Merge Here Take Your Turn” sign positioned about 350 feet prior to the transition area, ensuring drivers are well-informed and prepared to merge safely This approach enhances safety and efficiency during lane closures and road work zones.
Figure 7: Late Merge Layout (Source: Pesti, et al.)
McCoy and Pesti (2001) found that late merges resulted in 75% fewer forced merges and 30% fewer lane straddles at traffic densities below 25 vehicles per mile, indicating smoother traffic flow and increased driver cooperation As traffic density increased, these benefits diminished, but overall, late merging reduced aggressive driving behaviors and improved roadway capacity by nearly 20% Their study concluded that drivers exhibited greater willingness to cooperate when all drivers adhered to merging rules, leading to enhanced efficiency at congested intersections.
19 to Pesti et al (1999), queue lengths could be reduced by as much as 50 percent if both lanes were fully utilized up to the merging point
A study by Beacher et al (2004) found no significant difference in work zone throughput volume when using the late merge strategy, likely due to factors such as a low percentage of heavy vehicles (6.4%), proximity of ramps to the work zone, and the presence of intermediate traffic signals The impact of heavy vehicles on throughput was unclear, as they can either create large gaps or maximize lane storage capacity Lane straddling among trucks posed challenges, and most motorists did not adopt the expected merging behavior The study observed a slight increase of 5.1% in vehicles utilizing the closed lane during the late merge strategy, with many vehicles using the open lane to pass through the merge point more efficiently.
Pesti et al (1999) identified a significant difference in lane distribution patterns between trucks and passenger cars Specifically, 5% of trucks and 30% of passenger cars remained in the closed lane until reaching the W4-2 sign, located about 500 feet before the transition zone Additionally, only 18% of passenger cars stayed in the closed lane after passing the W4-2 sign, highlighting differing driver behaviors and lane utilization between vehicle types.
The late merge strategy significantly reduces traffic conflicts, primarily by decreasing the occurrence of forced merges and rolling blockades Specifically, using the late merge results in approximately 75% fewer forced merges and 30% fewer lane straddles compared to conventional merging methods Additionally, implementing the late merge enhances site capacity, increasing throughput to 1,470 vehicles per hour (vph) from 1,360 vph observed with traditional merging practices.
20 the conventional merge The researchers concluded that the late merge is more effective than the conventional merge in terms of safety and efficiency
Most late merge studies have been limited in assessing the full effectiveness of the strategy, as drivers typically do not utilize both lanes until reaching the merge point Drivers tend to reduce their speed and merge prematurely, often before the designated merge zone This behavior is likely influenced by roadwork signage instructing “Use Both Lanes Until Merge Point” and drivers’ negative perceptions of courteous behavior in the open lanes, which discourage them from following the late merge approach.
Safety concerns in the late merge design include the risk of two vehicles traveling at the same speed and approaching the merge point simultaneously, creating potential hazards The dynamic late merge concept aims to address this by adjusting merging strategies based on traffic volume, activating signs to inform drivers to use both lanes during high volume periods and reverting to conventional merging during low volumes However, the activation and deactivation of these signs can also pose safety risks, as slower vehicles in the open lane may merge into the closed lane with faster-moving traffic when signs are activated during high volumes, increasing the likelihood of conflicts and accidents.
The dynamic late merge strategy has been extensively tested by state agencies like MnDOT and MDOT, with mixed results MnDOT found that while this approach did not significantly impact travel time, it effectively reduced traffic volume within construction zones and decreased queue lengths by 35 percent Additionally, vehicles were nearly equally distributed near the merge point, indicating improved traffic flow and potentially enhanced safety during construction periods.
Implementing the dynamic late merge system in Minnesota has been shown to improve traffic flow and increase merging efficiency at the taper, according to MDOT studies Specifically, the strategy leads to a higher percentage of merging vehicles successfully merging, which enhances overall highway performance Additionally, significant reductions in travel time have been observed following the adoption of the dynamic late merge approach However, during peak evening hours, such as the P.M peak periods, no notable improvements were detected, indicating the strategy's variable effectiveness depending on traffic conditions.
The “Always Close Right Lane” strategy is widely utilized in Arkansas to improve traffic flow and safety during lane closures This method ensures drivers consistently close the right lane, allowing experienced drivers to anticipate the merging point and reduce sudden lane changes Once the first merge occurs, vehicles are guided to the appropriate lane opposite the construction zone, promoting smoother traffic movement Although empirical data on this strategy’s effectiveness is limited, studies indicate that the crash rate associated with the “Always Close Right Lane” approach is 46 percent lower than traditional lane closure methods (See, Schrock and McClure).
Crossover methods are implemented when all lanes in one direction are under construction, directing vehicles into an adjacent roadway and turning it into a bi-directional route for the duration of the work This exposes drivers to opposing traffic with minimal lateral separation, increasing safety risks To mitigate high-speed opposing traffic, a common strategy is the installation of a concrete median barrier along the work zone However, factors such as heavy traffic, nighttime visibility challenges, and adverse weather conditions pose additional safety concerns with this approach Moreover, this control method decreases lane capacity due to the close proximity of opposing traffic, impacting traffic flow efficiency (Pal and Sinha, 1996).
In the Netherlands, Belgium and Germany, alternating merge operations are known as “ritsen” or
During congested periods in Germany, drivers follow a “zipper rule,” allowing vehicles from adjacent lanes to merge alternately in a continuous lane, with right-of-way temporarily suspended until traffic eases This “zipper” maneuver is also employed in lane drop areas during uncongested times, where signage instructs drivers to begin merging approximately 1,500 feet before the lane closure to ensure smooth traffic flow.
Conclusion
Recent research emphasizes the ongoing need for effective work zone traffic control planning, highlighting that efficient merging strategies are essential for optimal operation of advance warning areas While tested merging strategies exhibit both benefits and drawbacks, the late merge and dynamic late merge stand out as the most effective and well-studied approaches These strategies have demonstrated advantages such as shorter queue lengths, increased capacity, and fewer forced merges, although they also present certain challenges that require further investigation Continued research is crucial to refine these strategies for improved traffic flow and safety in work zones.
A key issue associated with the late merge and dynamic late merge strategies is the frequent occurrence of non-compliant drivers These drivers often start merging prematurely, well before reaching the designated merging point, leading to potential disruptions and safety concerns on the roadway.
Table 3: Work Zone Traffic Control Merging Strategies
Type Intended Purpose Pros Cons
Alerts drivers of a lane reduction in advance of the transition area ahead
Insufficient during high volume periods Increases potential for rear end and side swipe crashes May increase queue lengths and aggressive driving
Encourages drivers to move into the open lane by placing additional warning signs further in advance of the transition area
May encourage drivers to use alternate routes which would decrease the approach volume
Insufficient during high volume periods Potential side swipe crashes Increase queue lengths and aggressive driving
L a te M er g e Encourages drivers to use both the closed and open lane until the transition area, at which time each driver is instructed to take turns merging
Decreases potential for rear end crashes and aggressive driving
May be hazardous during low volume periods Drivers do not comply with new strategy
The right lane is always closed during construction Drivers who are familiar with the rule know ahead of time which lane is closed
Less confusion on which lane is closed resulting in less potential for side swipe crashes
Insufficient during high volume periods Available space is not fully utilized
Detectors are used to produce real time traffic measurements, which triggers a series of flashing "Do Not Pass" signs in advance of the transition area when queues are detected
Manages the usage of lanes during low and high volume periods
Insufficient during high volume periods Available space is not fully utilized
D y n a m ic L a te M er g e Alternates merging strategies from the traditional merge to the late merge
Sensors detect approaching traffic volume to determine when to activate or deactivate traffic signs During high traffic volume periods, flashing signs instruct drivers to use both lanes to facilitate a late merge, improving traffic flow When traffic volume decreases, these signs are turned off, and the traditional merge protocol is reestablished, ensuring safe and efficient vehicle merging.
Sufficient during low and high volume conditions Decreases potential for side swipe and rear end crashes
Relatively expensive, requires longer setup time and periodic maintenance of sensors, there are concerns of confusion during the transition from the late merge to traditional merge strategy
Confusion between the signage and the arrangement of channeling devices often leads to unwanted merging behaviors on roads Although dynamic late merge signs promote the use of both lanes, channeling devices indicate that one lane terminates, causing drivers to believe that the open lane has priority This tendency to favor one lane over the other reflects a conventional merge strategy, which, during high traffic volumes, can result in congestion and increased risk of accidents Effective signage and clear lane design are essential to reduce driver confusion and improve traffic flow during merging scenarios.
• Decreased capacity, and high potential for rear end and side swipe crashes
Zipping, a merging technique that offers equal opportunity for motorists to access a lane without right-of-way priority, is believed to provide greater benefits and fewer negative effects compared to conventional merging methods Although the concept of zipping is relatively new in the context of open highway conditions in the United States, it has been successfully implemented for various applications across the country This innovative approach challenges traditional merging practices and has the potential to improve traffic flow and safety on U.S roadways.
The use of zipper merging techniques is increasingly popular across European countries, promoting traffic flow efficiency By evenly distributing vehicles into neighboring lanes and creating a smooth alternating pattern, each vehicle takes turns merging seamlessly This coordinated approach enhances safety and reduces congestion, especially in moderate-to-high traffic volume conditions.
A field test conducted by the Connecticut Department of Transportation demonstrated that an experimental sign depicting the zipping pattern can enhance merging behavior, improve safety, and optimize traffic flow at lane closures Notably, this was the only zipping study in the United States that directly assessed its effectiveness in real-world conditions, highlighting its potential benefits for traffic management.
This article discusses the design and evaluation of a new lane closure configuration implemented in a Louisiana work zone, featuring 30 merging operations within the transition area Key elements from the CDOT study and various merging strategies were incorporated to develop this innovative approach The chapter details the procedures used to design the new merge configuration and outlines the data collection methods employed at the test site to assess performance.
METHODOLOGY
Experimental Merge Design Selection
After evaluating the advantages and disadvantages of various work zone merging strategies, it was concluded that the most effective approach is one that is both cost-efficient and easy to understand, ensuring smooth traffic flow and reduced congestion.
Implementing effective merging strategies can significantly improve traffic flow and safety in work zones The late merge strategy has been shown to reduce queues and increase traffic flow by utilizing both lanes up to a designated point The "always close right lane" approach helps decrease driver confusion regarding lane closures, streamlining the merging process Additionally, the zipping concept, used in the CDOT Alternating Merge study, effectively reduces undesirable merges and encourages desirable ones The joint merge strategy combines these benefits by promoting lane utilization, minimizing confusion, and fostering cooperative driving behavior, ultimately aiming to enhance mobility and safety through better traffic management in work zones.
The joint merge is an essential traffic control plan designed for both temporary and long-term work zones to improve safety and efficiency It utilizes warning signage in the advance warning area and channeling devices in the transition zone to ensure an even distribution of vehicles across lanes By employing a series of warning signs and a "funnel-shaped" setup with traffic control devices at the transition zone entrance, the joint merge effectively combines two lanes into one This method enhances traffic flow and reduces congestion in work zone areas.
3.1.2 Selection of a Joint Merge Traffic Control Layout
Three alternative joint merge design schemes were presented to a committee of state and local traffic officials and researchers, with one scheme selected for testing at a work zone site These designs, detailed with diagrams in Appendix C, primarily differed in the transition zone design and sign placement, while maintaining similar overall structures Notably, Alternative One featured a single overhead flashing arrow board spanning the lanes, displaying two converging arrows to direct drivers effectively.
The transition zone was divided into two segments, the first simultaneously transitioned two lanes into one and the second shifted vehicles to the left away from construction
The W4-2 sign shown in Figure 4 was used in the second alternative joint design scheme
To effectively communicate lane merging, W4-2 directional signs were installed on both sides of the road—specifically, the 'Merge Right' sign on the right and the 'Merge Left' sign on the left The transition zone was divided into two segments: the first tapering two lanes into one to guide drivers smoothly through the merging area, and the second shifting vehicles to the left to direct traffic away from construction zones These measures enhance safety and traffic flow during lane closures and construction activities.
This study explored combining design elements from different schemes, such as integrating the overhead panel from Scheme One with the geometric layout of Scheme Two The third alternative design scheme successfully incorporated all essential components to create an effective joint merge This comprehensive design was selected for the study, with detailed descriptions of its joint merge components provided to ensure clarity and understanding.
Joint Merge Design Components
The traffic control plan for the joint merge configuration, as shown in Figures 13 and 14, differs from conventional traffic setups by incorporating physical channeling mechanisms that guide vehicles smoothly to merge Unlike late merge and zipper merge strategies, which primarily serve as traffic rules, the joint merge uses physical design features to naturally constrain vehicle movement Studies indicate that late merge rules are often inconsistently followed by drivers due to confusion and unfamiliarity, which is largely influenced by the physical configuration of traffic control devices.
The transition zone of the joint merge configuration is divided into three segments, highlighted in purple in Figure 15 The first segment gradually merges two incoming traffic streams into a single lane, while the second segment creates the illusion of a continuous lane before reaching the third segment In the third segment, vehicles are redirected left or right depending on construction needs; in this study, right lane closures are implemented, directing traffic to the left lane as shown in Figure 16 The lengths of these segments are L, ẵL, and ẵL respectively, with the total length L calculated based on lane width and posted speed limit using equation (1) According to MUTCD guidelines, the length of the shifting tapers, such as segment three, should be at least half the length of the merging taper in segment one to ensure safe and effective lane merging.
The joint merge design incorporated three experimental signs, including two textural signs—“Lane Closed Ahead” and “Both Lanes Merge”—to effectively communicate merging instructions to motorists Additionally, a symbolic joint merge sign designed by CDOT was used to enhance visibility and understanding of merging movements The CDOT-developed symbolic sign, shown in Figure 9, was selected for this project based on survey results conducted by CDOT, which validated its effectiveness in improving driver guidance and safety during lane reductions.
Two arrow boards were strategically placed on both sides of the transition zone entrance to effectively alert motorists of the upcoming lane reduction from two lanes to one This clear signage enhances driver awareness and promotes safety during the lane transition.
Figure 15: Joint Merge Traffic Control Plan 37
1 2 3 : Joint Merge Traffic Control Plan with Transition Zone Segment Coding
Figure 16: Segments 2 and 3 of the Joint Merge Transition Zone
In the work zone, arrow boards were followed by channeling devices spaced at forty-foot intervals, with the lateral distance gradually decreasing to sixteen feet from the entrance of the transition zone to the end of its first segment Louisiana state law mandates that all channeling devices used in work zones lasting over half a day be equipped with beacon lights operational during evening hours To comply with this regulation, beacon lights were attached to each channeling device throughout the study.
Changeable Message Boards (CMBs) are mobile units that display real-time, transcribed information to alert drivers about road conditions requiring extra attention When utilized effectively, CMBs are more impactful than static signage, providing timely and clear messages to motorists An effective CMB communicates essential information quickly and understandably, enhancing road safety and driver awareness (Ullman, Dudek, and Ulman).
2005) Guidelines expressed in the MUTCD should be used when placing CMBs, however, the specific details of CMB placement and procedures vary from state to state
During the installation and operation of the joint merge configuration, three CMBs were strategically positioned to enhance safety and traffic management The first CMB was installed half a mile before the initial advance warning sign, ensuring early driver alertness The remaining two CMBs were placed 1,500 feet prior to the first advance warning sign and just 210 feet before the third transition segment, providing clear guidance throughout the merging process Proper placement of these CMBs is essential for effective traffic flow and crash reduction in work zones.
The joint merge configuration was tested at the same location during two field tests Initially, the first message board displayed “Reduce Speed to 60 mph,” while the second message board consistently showed a series of messages: “Both Lanes Merge,” “Use Extreme Caution,” and “Road Work Ahead,” each appearing every three seconds, as illustrated in Figure 17 Additionally, the final message board near segment three continuously displayed “Lane Shifts to Left,” providing clear and consistent guidance to drivers during the test.
Figure 17: Second Changeable Message Board
During the second phase of the joint merge, three CMBs were installed and remained until the configuration was removed, effectively conveying key traffic messages to drivers Although phrased slightly differently at the discretion of LA-DOTD maintenance staff, all CMBs communicated consistent instructions The first CMB instructed drivers to “Reduce Speed to 60 mph,” while the second displayed alternating messages every three seconds: “Lanes Merge to Center” and “Use Extreme Caution,” to alert motorists of upcoming lane changes The third CMB in segment three combined text and symbols, displaying “Lane Shifts” alongside arrows pointing left, clearly indicating the direction of lane shifts for driver awareness.
To ensure consistency between designs for accurate comparative analysis, the placement of signs in the conventional merge configuration closely matched their positioning in the joint merge configuration test The specific sign positions are detailed in Table 4.
Table 4: Placement of Static Signs for the Conventional and Joint Merge
Signs Distance in Advance of Transition Zone
“Road Work 1 Mile” 1 mile 1 mile
“Speed Zone Ahead” 3,400 feet 3,400 feet
“ (Right) Lane Closed Ahead” 2,600 feet 2,600 feet
Illustrated Sign (W4-2 or Experimental) 1,000 feet 1,000 feet
“Speed Limit XX” 2,600 feet 1,800 feet
“Both Lanes Merge” 1,800 feet NA
The merge configurations necessitated modifications to the placement of key advance warning signs, including the “Speed Limit XX” and “Both Lanes Merge” signs When transitioning from the conventional to the joint configuration, the “Speed Limit XX” sign was replaced with a “Both Lanes Merge” sign and relocated 1,600 feet upstream to improve traffic safety and ensure clear driver communication.
Site Selection
Selecting a suitable site is crucial for accurate analysis, as uncontrollable roadway elements and external disturbances like nearby interchange ramps and uneven terrain can bias results Choosing the proper test location reduces the impact of surrounding environmental factors on travel behavior To identify the ideal site, specific criteria were established, emphasizing the importance of minimizing external influences and ensuring reliable data collection for the study.
1 Active construction work on rural freeways;
2 Two-to-one lane closures;
3 Recurring periods of congestion and queuing;
4 Adequate space along the shoulder for set up of data collection devices;
5 Limited access to entrance and exit ramps within or near the study area; and
6 Relatively straight horizontal and level vertical alignments
This study selected a site within approximately 100 miles of Louisiana State University, specifically on Interstate 55 north of Hammond between mile markers 33 and 36 The research focused on merge configuration experiments initially developed for routine road maintenance projects; however, it did not analyze traffic behavior in active work zones due to scheduling conflicts between LA-DOTD, contractors, and researchers Instead, "dummy" work zones—areas without any ongoing construction—were utilized for the study.
Description of the Study Site
This study was conducted on a straight, level segment of I-55 to effectively eliminate the effects of roadway curvature The testing area spanned 7,704 feet, with the nearest onramp located 250 feet before the study section and the closest off-ramp positioned two miles downstream.
According to Louisiana Department of Transportation and Development (LA-DOTD) the
2007 average annual daily traffic counts north bound on I-55 near the study site was approximately 20,858 vehicles per day (vpd) During normal operations, the posted speed limit is
70 mph, but when lane closures are present the posted speed limit is changed to 60 mph
Throughout the study, researchers periodically visited the site to capture video footage of merging events, providing valuable insights into traffic behavior Observations also included evidence of vehicular crashes, such as tire marks, dismembered beacon lights, and displaced channeling devices, indicating crash occurrences These crash-related findings will be incorporated into a separate safety study currently in progress, enhancing overall traffic safety analysis.
During lane closures, LA-DOTD road-maintenance personnel conducted daily site visits to ensure traffic control devices were operating correctly, typically inspecting the site once during the day and once in the evening to maintain safe traffic flow.
Five detection zones were established to monitor traffic flow, with four zones (Zone A, Zone B, Zone C, and Zone D) located in advance of the transition zone and one zone (Zone E) positioned immediately after the transition These zones are clearly illustrated in Figure 18, with each zone labeled sequentially from Zone A, the first zone before the initial warning sign, to Zone E, which is after the lane reduction from two lanes to one is completed This systematic placement ensures comprehensive detection and monitoring throughout the transition process.
43 the advance warning area, and it represents the traffic behavior under normal driving circumstances not influenced by any signage or lane closures
Vehicle Magnetic Imaging Recorders (MIRs) are advanced, self-contained sensors installed under a protective rubber cover in the center of traffic lanes, requiring no external equipment or physical contact from vehicles These sensors utilize magnetic imaging technology to detect and monitor passing vehicles by sensing disturbances in the Earth's magnetic field caused by iron components within vehicles MIRs can accurately record essential traffic data such as vehicle presence, speed, type, and length, as well as count the number of vehicles passing through a given point Additionally, MIRs provide valuable environmental data by reporting road surface temperature, making them a comprehensive tool for traffic monitoring and analysis.
Our sensors accurately record vehicle speeds and lengths with 90% precision, within a margin of plus or minus four miles per hour and four feet, ensuring reliable traffic data Vehicle counts are reported with an impressive 99% accuracy, providing essential insights for traffic management The units have a maximum storage capacity of 300,000 vehicles or 21 days of data, whichever comes first, enabling continuous monitoring without data loss Headways are calculated internally based on vehicle counts and speed information, allowing for precise traffic flow analysis Additionally, the system automatically identifies stopped vehicles by flagging those moving below eight miles per hour, enhancing incident detection and traffic safety.
Figure 18: Established Zones Used for Traffic Control Plan Analysis
An over-the-counter hard disk drive camcorder was installed on an overpass facing the opposite direction of travel, capturing merging events from the start of the transition zone to the study site The camera’s range, as shown in Figure 19, allowed for comprehensive coverage of the merging area Recorded video footage was used for both qualitative and quantitative analyses, supplementing data collected by Milepost Impact Recording (MIR) devices During each site visit, approximately two hours of video were captured, including periods during installation and removal of lane closures In total, this effort resulted in over ten hours of valuable video recordings under lane closure conditions, providing detailed insights into vehicle merging behavior.
Figure 19: Entry into Transition Zone of the Joint Merge Configuration
This study involved a labor-intensive data collection process that required significant effort, particularly in installing MIRs Challenges such as holiday periods causing increased traffic, adverse weather conditions, and the availability of LA-DOTD road-maintenance personnel impacted the installation process.
To enhance safety near the installation crew, it was observed that 46 vehicles were speeding in the area The study aimed to collect lane-specific traffic information across multiple zones within the site, which necessitated implementing comprehensive safety measures to ensure data accuracy and protect personnel during the data collection process.
Arrow boards, initially utilized during MIR sensor installations, served as effective traffic control tools alongside static signs A truck-mounted arrow board was strategically placed at least half a mile before the installation area to direct motorists away from the work zone; for instance, if MIRs were installed in the right lane, the arrow board pointed left to guide drivers accordingly To ensure safety, at least five LA-DOTD maintenance personnel were evenly spaced from the arrow board to the installation site, with maintenance staff actively flagging motorists in the opposite lane to provide additional security for the installation crew.
The MIRs were attached to the middle of the lane using the following tools:
3 Hammer Drill and 5/8” drill bit
An electric hammer drill powered by a gas generator mounted on a truck was used to create two-inch deep holes for the installation During drilling, a leaf blower was employed to clear away residue, which previous tests showed could hinder screwing Afterward, screw-anchors were inserted into the prepared holes The MIRs were then encased in protective rubber covers and securely attached to the lane with screws, washers, and a ratchet set This installation process was repeated seven times, with detailed steps illustrated in Figures 21 and 22.
Figure 20: Flaggers near the Installation of MIRs
Sensor placement focused on locations near other sensors in adjacent zones and areas with high lane-changing activity to ensure effective data collection Strategically, sensors were positioned close to signs conveying critical information, as motorists tend to respond to messages they find noteworthy Key signs targeted included “Lane Closed Ahead,” “Speed Limit XX,” and symbolic right lane closed signs, which are most likely to influence driver behavior and improve traffic management.
The sensor, encased in a protective rubber cover, was securely attached to the lane using screws, washers, and a ratchet set This installation process was repeated seven times at different locations to ensure consistent placement Visual documentation of the sensor and installation procedures is provided in Figures 21 and 22.
Sensor placement locations were strategically chosen based on existing traffic signs, proximity to other sensors, and zones with frequent lane changes, as these areas are where motorists are most responsive to noteworthy information Key signs such as “Lane Closed Ahead” and “Speed Limit XX” were identified as highly influential in driver behavior, making them ideal locations for sensor installation Sensors were encased in protective rubber covers, securely mounted to lanes with screws and washers, ensuring durability in busy traffic zones Images of the sensors and signs helped verify optimal placement, aligning sensor locations with areas where drivers are most likely to respond to important signage, thereby improving traffic monitoring and safety.
Figure 21: Example of the Installation Process
Figure 22: Attached MIR with Protective Cover
In all zones except ZONE E, which featured only a single lane and sensor, two MIR sensors were installed per zone These sensors were positioned directly opposite each other in the center of each lane, ensuring optimal coverage An example illustration of the mounted MIR sensors is provided in Figure 23, with their specific zonal locations detailed in Table 5.
Table 5: Placement of MIR Sensors for Both Merge Configurations
Zone MIR Sensors Distance From the Beginning of the Taper
A 1 and 2 1500’ before first advance warning sign
1500’ before first advance warning sign
Note: *Denotes that the distance is measured in the direction of traffic from the beginning to the end of the transition zone
Data Collection
Work activity at a construction site can significantly reduce roadway capacity, negatively impacting traffic flow in areas approaching the transition zone (Dixon, Hummer, and Lorscheider, 1996) Reduced capacity from active construction zones often causes long queues that quickly propagate backwards, disrupting traffic operations To ensure accurate analysis of merge configurations, this study was conducted in an inactive work zone, as uninfluenced roadways provide more reliable data for traffic flow assessments.
This study was conducted over eight months, involving the collection of more than 600 hours of data across multiple locations within the designated study area Collaborating with the Louisiana Transportation Research Center and the Hammond District of LA-DOTD, researchers gathered extensive data specifically from the north-bound lanes of I-55 To ensure data accuracy, information recorded during rainy periods was excluded from the analysis, as it was believed to introduce unexamined variables that could impact results.
The study involved a comprehensive analysis of traffic control configurations, including ten days of deploying channeling devices and signs to match conventional right lane closure plans The same location was used for setting up and evaluating the joint merge configuration, which was analyzed across two separate periods totaling eighteen days To ensure accurate results, at least three weeks of normal freeway operations without lane closures were incorporated between data collection phases, minimizing the risk of traffic behavior transfer and biasing the study outcomes.
Data collection combined established techniques and insights gained from prior research and practical experience The study hypothesized that lane closure efficiency is influenced by total traffic volume and vehicle positioning near the transition zone Consequently, lane-specific volume and speed data for both configurations were recorded in 60-minute intervals to analyze their impact on traffic flow.
• Programming Speed Groups in the MIRs
MIRs utilize up to fifteen predefined speed groups to accurately record and average vehicle speeds hourly During the study, many motorists exceeded the posted speed limit of 60 mph, with some traveling over 80 mph The speed groups listed in Table 6 were specifically programmed into the MIR units to effectively capture the range of vehicle speeds at the study site, ensuring comprehensive data collection for analysis.
Speed Group Miles Per Hour
Typically, volumes are classified as belonging to one of three categories low, medium or high
To enhance the analysis, the study increased the number of volume classes from four to six, providing a more detailed categorization The six volume groups were created with equal increments of 300 vph, covering flow rates up to a maximum of 1,672 vph, to ensure balanced representation of volume contributions in the merge configurations This approach improves the accuracy of flow analysis and operational insights, as detailed in Table 7.
Volume Class Vehicles Per Hour
Sensor data were systematically extracted and organized into a spreadsheet through a series of ordinal steps, including grouping by merge configuration type, time of day, zones, volume classification, and lane orientation (right or left lane) Statistical analyses, such as T-tests and ANOVA, were conducted at a 95% confidence level to compare the different groupings based on speed and volume Data segments lacking complete data sets within specific time intervals were excluded from the analysis to ensure accuracy and reliability.
Measures of Effectiveness
The primary goal of the joint merge configuration was to preserve the natural traffic flow characteristics of the pre-work zone, ensuring that the lane closure did not disrupt existing traffic patterns Implementing a lane closure was anticipated to negatively impact traffic operations, potentially causing congestion and delays By maintaining the pre-closure traffic conditions, the design aims to minimize disruptions and ensure smooth traffic movement through the work zone.
1 Relatively safe and uniform speeds unchanging as vehicles travel through roadway segments, and
These flow characteristics were used to select appropriate measures of effectiveness for the study, which were average speed, flow rate, and vehicle lane distribution
The joint merge was designed to improve speed consistency in both open and closed lanes as vehicles pass through each zone Comparative analysis showed significant differences in average speed changes between the joint and conventional configurations across various zones, lanes, and traffic volumes Statistical tests detailed in Chapter 4 confirm the effectiveness of the joint merge in maintaining higher and more stable speeds, demonstrating its potential to enhance traffic flow and safety.
The queue discharge rate, which occurs during congested periods, represents the hourly flow rate of vehicles after capacity has been exceeded According to Jiang (1999), this measure provides a more accurate assessment of corridor efficiency than flow rates observed during uncongested conditions Therefore, analyzing the queue discharge rate is essential for understanding traffic flow dynamics during congestion and optimizing lane closure capacity studies.
Congested periods occur once traffic capacity is exceeded, often identified using time-stamped speed data Previous research indicates that capacity is characterized by the flow rate just before a significant speed reduction followed by sustained low speeds (Jiang, 1999; Dudek and Richards, 1982; Al-Kaisy, Zhou, and Hall, 2000) According to Maze et al (2000), current speed-flow models, such as those in the Highway Capacity Manual, show maximum flow when speeds decrease by approximately 14% This study defines congestion as periods with a speed drop of 14% or more, during which the queue discharge rate reaches its highest levels.
This study analyzed the observed flow rates during congested periods, averaging queue discharge rates across different configurations T-test analysis was employed to compare these rates and identify significant differences An example of a selected queue discharge rate used in the analysis is illustrated in Figure 24, providing insight into flow behavior during congestion.
Figure 24: Example of Speed / Time and Volume / Time Graph Used in Selecting
Figure 24 presents a line graph illustrating the relationship between speed and time (purple) and volume and time (red) A notable decrease in speed occurs at 15:00 hours, with recovery not observed until 18:00 hours, indicating a congestion period from 3:00 p.m to 6:00 p.m During this peak congestion, the highest flow rate recorded was approximately 1,672 vehicles per hour This flow rate was subsequently averaged with other maximum flow rates observed during different congested periods to analyze overall traffic patterns.
Channeling devices in the joint merge configuration were strategically arranged to ensure balanced lane volumes across all zones, regardless of traffic volume levels This setup aimed to distribute approximately 50% of the total traffic through the closed lane at each zone during both low and high traffic periods The percentage of vehicles utilizing the closed lane in both configurations was carefully measured and analyzed Detailed results and data tables are provided in Appendix B.
Maximizing flow rate in a traffic segment occurs when there is an even 50/50 distribution of vehicles between lanes Studies indicate that less than 5% of drivers enter the transition zone from the closed lane in traditional merge setups Statistical analyses, including ANOVA and T-tests, compared joint and conventional merge configurations to assess their effectiveness in encouraging 50% of motorists to remain in the closed lane continuously The vehicle percentages in the closed lane were analyzed across different zones and volume levels to evaluate performance.
This study evaluates the impact of the joint merge configuration on traffic operations within a work zone’s advance warning area, highlighting its potential to better maintain smooth traffic flow compared to conventional merge setups Several analytical measures were employed to assess how the joint merge influences traffic performance under different conditions The subsequent analysis details the statistical testing methods used to compare the two merge configurations, ensuring a robust evaluation of their effectiveness Results from these tests demonstrate the advantages and limitations of both merge types, providing valuable insights for optimizing traffic management in work zone environments.