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Design Guidelines for Maintenance of Traffic through Construction Zones (aka Temporary Traffic Control)

Description:

Maintaining traffic during construction in a constrained roadway environment is a common practice. Often, work is needed on or near existing lanes of traffic, and the traffic lanes must be moved to perform the needed construction. In many cases, limited room is available to maintain traffic. Shoulders, temporary widening, median crossovers, and temporary alignments are used to avoid road closures, detours, or reducing the number of lanes available to traffic. These temporary conditions can be short-term, intermediate, or long-term durations. Many designers do their best to fit a solution to maintain capacity of a road. The need is more prominent on higher-speed facilities such as freeways and expressways, and it becomes more complicated near entrance and exit ramps. The engineers and designers use available resources such as the MUTCD to introduce lane shifts and closure tapers in the work zone. A few agencies have specified that superelevation (SE) transitioning can use Method 2 SE transitions instead of Method 5 transitions for temporary alignments. Method 2 assumes drivers will accept more discomfort for a temporary construction condition and relies on side friction to the vehicles in curves more so than Method 5 SE transitioning (which is used by most agencies for permanent design). A few other guidelines may be found from agency to agency regarding temporary conditions regarding to permitting narrower lanes in some conditions and some requirements for barrier placement and drop offs near live traffic.

What has been found is that most agencies do not have much guidance available to the engineer regarding temporary geometric design criteria. That often puts engineers in a position to attempt to use design criteria developed for permanent conditions (e.g., those found in the AASHTO Green Book, their State Highway Design Manual, or local standards) or to use a design based on their best judgment or something another agency may have allowed. Guidelines for temporary conditions based on research would be preferred, as this is a reoccurring condition for roads in every jurisdiction. The profession should evaluate what guidelines for temporary conditions should use those specified for permanent conditions and what guidelines may allow for something less. Criteria that need to be examined for temporary conditions include:

· Validating the use of Method 2 SE transitions (including running traffic on lanes with adverse crown – such as an outside shoulder sloping away from the median in a curve to the left).

· Allowable grades.

· Cross-slope breaks (between lanes or even within a driving lane).

· Ramp terminal acceleration and deceleration distances.

· Taper rates.

· Sight distance.

Related questions that could be addressed with temporary traffic control guidelines include:

· Are there any specific locations where traffic control devices must be included or avoided (including regulatory signs)?

· Are engineers using permanent condition criteria when they could be using something less? This could be increasing the cost for the temporary design.

· Are engineers using a design that may not be the safest option in order to fit a solution to the space available?

Having guidelines available for temporary conditions is desirable from an operational standpoint (keeping the traffic moving), from an agency/designer standpoint (reducing their liability by utilizing recognized design research – not under-designing), and a cost standpoint (so temporary conditions are not over-designed).

Designers often overlook drainage impacts of these temporary lane shifts. Often concrete barriers are used to separate the construction work zone from traffic without much consideration of the effect on drainage patterns. Additionally, these lane shifts often do not have shoulders to carry stormwater runoff and therefore localized flooding may occur within the lane transitions. Additional guidance is needed to accommodate drainage considerations for various duration closures, especially those that may be subject to winter driving conditions.

With advances in vehicle and infrastructure technology, a portion of this research should examine what, if anything, needs to be incorporated into the Maintenance of Traffic (MOT) design considerations to aid or facilitate autonomous and connected vehicles through a work zone. What additional traffic control devices may be needed for the vehicle recognition software to recognize the lane transition, especially when horizontal clearances may be limited? The research should evaluate what may need to be incorporated in the MOT design for effective implementation in the field (one possibility raised by the authors of this research needs statement was whether a constant temporary stripe [e.g., 6 inches wide to be recognized by autonomous vehicles] might be needed along each outside edge of a particular direction of traffic).

Objective:

The objective of this research is to provide geometric design criteria for temporary lane configurations needed during construction activities. The research would be helpful to the transportation design professional and facility owners. The findings may lead to modification of the currently used design criteria or creation of design criteria. This could lead to more uniform design practices, a reduction in design risk, and possibly a reduction in costs (for those agencies that may currently be over-designing for temporary conditions). Some agencies also have a process to deviate from design criteria that is also used for temporary conditions. This research may reduce the number of exceptions to those criteria. The results of the project should be developed in a manner that allows it to be directly used within future updates to the AASHTO Green Book and the Manual on Uniform Traffic Control Devices.

Benefits:

This is an urgent matter as this is an ongoing problem area on most construction projects on high-speed facilities. This research need has been identified as a high priority by the AASHTO Technical Committee on Geometric Design, the TRB Committee on Geometric Design, and the TRB Committee on Operational Effects of Geometrics at their July 2016 combined meeting and again at their June 2018 joint meeting. The research is needed to provide enhanced guidance that will directly affect the design of maintenance of traffic plans for high-speed facilities. The potential payoff is the selection of lower risk, more consistent, and more cost efficient designs.

The AASHTO Standing Committee on Research – NCHRP’s governing body – will select projects based on two key factors: the potential value of the research results and the likelihood of implementation-ready products. This section should describe the anticipated product and the potential benefits if the research is completed successfully and the products deployed. It should also discuss the potential negative impacts if this problem statement is not funded.

Related Research:

A literature review indicates that some state agencies have adopted some permanent design criteria (often from the AASHTO “Green Book”) or have developed standards and criteria utilizing something less than the criteria within. It is unlikely the lesser conditions are based on design research for temporary conditions. The following state transportation agencies were found to have some temporary design guidelines; however, the guidelines are limited:

o Illinois Department of Transportation (BDE Manual)

o CALTRANS (Design Manual)

o Florida Department of Transportation (Design Manual)

o Texas Department of Transportation (Design Manual)

o Pennsylvania Department of Transportation (Traffic Engineering Manual)

o Illinois State Toll Highway Authority (MOT Manual)

o Ohio Department of Transportation (Traffic Engineering Manual – Part 6, and Ohio Manual of Uniform Traffic Control Devices)

The Institute of Transportation Engineers included a chapter in the 6th edition of the Traffic Engineering Handbook on Maintenance of Traffic Design.

Guidelines on Motorcycle and Bicycle Work Zone Safety. Workzone.org.

Other more research-focused resources include:

o Traffic Control Strategies in Work Zones with Edge Drop-Offs. Sponsored by the Office of Traffic and Safety, Iowa Department of Transportation. Center for Transportation Research and Education. CTRE Final Report, August 2002, CTRE Project 97-15.

o Work Zone Operations Best Practices Guidebook (Third Edition). Publication No. FHWA-HOP-13-012 August 2013. USDOT.

o Design of Construction Work Zones on High-Speed Highways. NCHRP Report 581. 2007.

o NCHRP Web-Only Document 105. Final Report for NCHRP Report 581: Design of Construction Work Zones on High-Speed Highways. October 2006

Tasks:

Some of the tasks that could be completed in this project proposal include:

· Completion of a comprehensive literature review and summary of current practice. This should include both international domestic resources and practices. This review should also identify locations with operational and crash history for temporary design conditions.

· Identify if temporary design criteria should be the same as permanent design criteria or if criteria for long-term, intermediate, or short-term traffic control conditions are recommended.

· To identify this information, an owner/agency survey will likely be needed.

· Develop and perform owner/agency survey.

· Evaluate the collected data.

· Determine a way to study data in order to make a recommendation on design criteria for:

o Horizontal curves (with a special focus on Method 2 superelevation transitions).

o Cross-slope breaks (between lanes and within a lane)

o Ramp terminal design.

o Acceleration and deceleration near ramps.

o Lane shifts.

o Tapers (especially closures).

o Grades.

o Regulatory and guide sign placement.

o Temporary traffic control device placement.

o Use of temporary stripes vs. drums and barricades (especially in ramp gores).

o Temporary drainage strategies that may need to be deployed.

o Additional considerations for autonomous vehicle recognition software related to temporary lane conditions

· Provide recommendations for various geometric design elements.

· Propose new text for the next edition of the AASHTO Green Book based on the results of the research project.

Implementation:

All engineers, designers, agencies, and contractors involved in the design or implementation of maintenance of traffic plans on high-speed facilities will be impacted by this research. In addition to the component of the research to investigate the implications to autonomous and connected vehicle technologies, this also will be important to automobile and other vehicle manufactures. Few barriers to this research are expected as few agencies currently have design criteria (especially based on research) for temporary conditions.

Sponsoring Committee:AKD10, Performance Effects on Geometric Design
Research Period:12 - 24 months
Research Priority:High
RNS Developer:David McDonald, Jason Hodges, Alan Glen
Source Info:This problem statement was developed in connection with the June 2018 mid-year joint meeting of the AASHTO Technical Committee on Geometric Design, the TRB Committee on Geometric Design (AFB10), and the TRB Committee on Operational Effects of Geometrics (AHB65).
Date Posted:09/21/2018
Date Modified:12/31/2018
Index Terms:Geometric design, Work zone traffic control, Work zones, Autonomous land vehicles, Intelligent vehicles, Connected vehicles,
Cosponsoring Committees: 
Subjects    
Highways
Design
Operations and Traffic Management
Safety and Human Factors

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