Geometric Design Guidelines During Construction, Maintenance of Traffic (aka Temporary Traffic Control) Design
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.
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”).
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.
The potential payoff is the selection of lower risk, more consistent, and more cost-efficient designs.
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
Department of Transportation, BDE Manual
Department of Transportation Design
Department of Transportation Design
Department of Transportation. Traffic
State Toll Highway Authority, MOT Manual
Department of Transportation, Traffic
Engineering Manual (TEM) – Part 6
Department of Transportation, Manual on
Uniform Traffic Control Devices (OMUTCD)
Department of Transportation, Facilities
Design Manual – Chapter 11: Design
of Transportation Engineers Traffic Engineering
Handbook, 6th edition – Chapter on Maintenance of Traffic
on Motorcycle and Bicycle Work Zone Safety, Workzone.org.
Other more research-focused
· 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.
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
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 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
· Provide recommendations for the various geometric design elements listed
· Propose new text based on the results of the research project for the
next edition of the AASHTO Green Book.
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.
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|
|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.|
|Index Terms:||Work zone traffic control, Geometric design, Highway design, Highway capacity, Temporary barriers, Detours, Manual on Uniform Traffic Control Devices, Freeways, |
Operations and Traffic Management
Safety and Human Factors