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Geometric Design Guidelines During Construction, Maintenance of Traffic (aka Temporary Traffic Control) Design

Description:

Maintaining traffic during construction in a constrained environment is becoming common. Often, during these maintenance and construction activities work is needed on or near existing lanes of traffic and the traffic must be moved from these locations to perform the needed improvement. In many cases, limited room is available to maintain traffic. Shoulders, temporary widening, crossovers, and temporary alignments are utilized to avoid creating 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 something in to maintain a movement and maintain capacity of a road. The need is more prominent on higher speed facilities such as freeways and expressways and becomes more complicated in the vicinity of on- and off-ramps. The engineers and designers use available resources such as the Manual on Uniform Traffic Control Devices (MUTCD) to introduce lane shifts and closure tapers in the work zone. A few agencies have specified that superelevation 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 more 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. Some agencies use a reduced design speed, such as 10 mph less than the permanent facility design speed, to define temporary conditions.

Based on these findings, the conclusion is that most agencies do not have much more criteria available to the engineer regarding temporary geometric design criteria. That puts the engineer in a position to attempt to utilize design criteria developed for permanent conditions (often those found in the AASHTO Green Book) or to use something less 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 all of our roads. The authors 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 are: 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 breakover (between lanes or even within a driving lane), ramp terminal acceleration and deceleration distances, taper rates, and sight distance. Are there any specific locations where traffic control devices must be included or avoided (including regulatory signs)? Are the engineers utilizing criteria for permanent conditions, when in fact they could be using something less? That could be increasing the cost for the temporary design. Are the engineers trying to fit something in that may not be safe in order to just have a solution? Having guidelines available for temporary conditions is desirable from an operational aspect (keeping the traffic moving), from an agency/designer perspective (reducing their liability by utilizing recognized design research – not under-designing), and from a cost perspective (so that temporary conditions are not over-designed).

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 to aid or facilitate autonomous and connected vehicles through a work zone. At this time, we don’t know what this may be, but the research should look into what may need to be incorporated into MOT implemented in the field that should be specified and considered by the design (one possibility raised by the authors of this research needs statement was “might a constant temporary stripe 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 conditions. 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 a reduction in design risk, more uniform design, and could lead to reduced costs (for those agencies that may currently be over-designing for temporary conditions), and reduce ROW needs. 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 that 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:

The potential payoff is the selection of lower risk, more consistent, and more cost-efficient designs.

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 and national transportation agencies were found to have some temporary design guidelines:

· Illinois Department of Transportation, BDE Manual

· CALTRANS, Design Manual

· Florida Department of Transportation Design Manual

· Texas Department of Transportation Design Manual

· Pennsylvania Department of Transportation. Traffic Engineering Manual

· Illinois State Toll Highway Authority, MOT Manual

· Ohio Department of Transportation, Traffic Engineering Manual (TEM) – Part 6

· Ohio Department of Transportation, Manual on Uniform Traffic Control Devices (OMUTCD)

· Wisconsin Department of Transportation, Facilities Design Manual – Chapter 11: Design

· Institute of Transportation Engineers Traffic Engineering Handbook, 6th edition – Chapter on Maintenance of Traffic Design.

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

Other more research-focused resources include:

· 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.

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

· Design of Construction Work Zones on High-Speed Highways. NCHRP Report 581, National Cooperative Highway Research Program. 2007.

· Final Report for NCHRP Report 581: Design of Construction Work Zones on High-Speed Highways. NCHRP Web Only Document 105, National Cooperative Highway Research Program. 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 and 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.

· Develop and perform owner/agency survey to supplement the information from the two tasks above.

· Evaluate the collected data.

· Analyze data with an emphasis on design criteria for:

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

o Rollover (between lanes and within a lane)

o Ramp terminal design

o Acceleration and deceleration in the vicinity of ramps.

o Lane shifts

o Tapers (especially closures)

o Grades

o Design Speed

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).

· Provide recommendations for the various geometric design elements listed above.

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

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 manufacturers. Few barriers to this research are expected as few agencies currently have design criteria (especially based on research) for temporary conditions.

Relevance:

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. The research is needed to provide enhanced guidance that will directly impact 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.

Sponsoring Committee:AKD10, Performance Effects on Geometric Design
Research Period:12 - 24 months
Research Priority:High
RNS Developer:David McDonald, Jason Hodges, Richard Coakley
Source Info:Developed as part of the 2016 mid-year meeting of the TRB Committee on Geometric Design (AFB10), TRB Committee on Operational Effects of Geometrics (AHB65), and AASHTO Technical Committee on Geometric Design.
Date Posted:10/26/2016
Date Modified:11/14/2016
Index Terms:Work zone traffic control, Geometric design, Highway design, Highway capacity, Temporary barriers, Detours, Manual on Uniform Traffic Control Devices, Freeways,
Cosponsoring Committees: 
Subjects    
Highways
Construction
Design
Operations and Traffic Management
Safety and Human Factors

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