American Association of State Highway and Transportation Officials
Special Committee on Research and Innovation
FY2023 NCHRP PROBLEM STATEMENT TEMPLATE
Problem Number: 2023-G-18
Problem Title
LED Applications on Traffic Control Devices
Background Information
and Need For Research
The use of LED’s has been expanded into the
traffic control area with units used to enhance attention/conspicuity of signs,
create dynamic sign legends, and provide basic traffic control. The Manual on
Uniform Traffic Control Devices (MUTCD) administered by the FHWA has contained
limited LED provisions to guide the LED applications This has created some
indecision among public agencies relative to the appropriate application of
LED’s in their traffic control applications. The NCUTCD has submitted LED
recommendations to FHWA that maintain basic traffic control concepts, recognize
the adaptability of LED technology and provide guidance for LED use. The
development of those MUTCD recommendations identified a number of issues where
research was not available to support the recommendations. There continues to
be growing use of LED signs without clear understanding of possible safety
advantages and/or impacts to automated vehicles, road users and adjacent
residents. This research is needed to provide industry clarification on the LED
applications and guide roadway agencies on basic traffic control concepts that
ensure life cycle of significant investments and safety to road users.
Literature Search
Summary
A literature search on the TRID database
identified limited research that have addressed the LED design issues
identified below. Most of the prior work focuses on design rather than
consequence of LED applications. The following studies partially reviewed the
application of LED’s but provided little to no information on emerging issues
noted in this problem statement.
A. Texas Transportation Institute (TTI)
TTI has conducted a number of research studies
that utilized LED’s beginning with Report FHWA/TX-04/4271-1, October 2003,
Traffic Operational Impacts of Higher Conspicuity Sign Materials, on LED Stop
signs and red border Speed Limit signs. A 2004 report, Project No. 404940,
Legibility Distances of Smaller Character Light-Emitting Diode (LED) Dynamic
Message Signs for Arterial Roadways, recommended that the City of Dallas should
not reduce the legend size. Report FHWA/TX-12/0-6462-1, December 2011, Modern
Traffic Control Devices to Improve Safety at Rural Intersections, provided some
guidance on usage of embedded LED’s on STOP signs. Project FHWA/TX-12/0-6407-1, January 2012,
Studies to Determine the Effectiveness of Automated Flagger Assistance Devices
and School Crossing Devices, addressed various configurations and LED applications
for STOP/SLOW paddles.
B. Transportation Association of Canada
The Transportation Association has sponsored
two research studies. TOMSC No. 293, Appropriate Use of Blinking Border Lights,
April 2010, provided some recommendations on border LED applications and the
Final Report, September 2010, provides some recommendations on usage, flash
rate, pattern, color, number and placement, and intensity.
Research Objective
The objective of this research is to evaluate
various LED sign applications and provide research data that supports the best
LED application on regulatory and warning signs for the road user. The issues
to be researched are identified below in priority order with the scope of the
research subject to change because of limited funding. A research plan for each
issue should be developed and approved.
The issues to be considered in the research are
as follows:
1. Refresh
Rate: LEDs refresh at a rate that is not observable by human eyes (typically
above 60 Hz). However, at these rates detections systems for automated vehicles
see blank images due to the “slow” refresh rates. This applies to CMS as well
as traffic signal and beacon displays (in addition to street lighting and
vehicle lighting which may affect automated vehicle perception devices –
sensors, cameras, software). A 200 Hz minimum rate has been proposed without
research into secondary impacts to radio frequency standards set by FCC Part 15
due to power loads. Future misinterpretations of traffic control or vehicle
lighting/turn displays would pose a public safety risk. Because of the
significant cost of CMS, signs could become obsolete without clear
understanding of refresh rates, machine detection and radio frequencies. What
is the optimal refresh rate for LEDs in traffic control applications and how
can this be shared across street lighting and vehicle lighting use?
2. Flash
Rate: The recommended MUTCD (Section 2A.07) flash rate varies from 50 to 120
times per minute. Rectangular Rapid Flashing Beacons (RRFB’s) have interim FHWA
approval for a unique flash rate at pedestrian crosswalks. Would different
specified flash rates for beacons based upon groups of signs such as stop,
warning, or pedestrian to identify the sign application be beneficial for the
road user?
3. Flash
Pattern: In addition to flash rate, flash patterns are utilized for various
traffic control devices. Basic flashing is where illuminated elements are
simultaneously on and then off repeatedly at fixed intervals (flash rate).
Coordinated flashing can occur in four different ways: a) sequential flashing where
flashing elements of the sign progressively display a message either within a
sign or from sign to sign (for example W1-8 Chevrons in a curve); b)
alternating or dancing flashing where the same symbol or beacon is displayed in
different horizontal position (for example alternating diamonds); c) rapid
flashing where the flash rate differs from simultaneous (for example a
rectangular rapid flash beacon); and d) streaming flashing where a symbol is
displays progressively across a CMS multiple times (different from a single
change which would be alternating, for example portable temporary traffic
control using sequential chevrons). When should the various flash rates be
applied to produce the best outcomes for safety? Should these flash rates be
unique to single traffic control devices or applications to have maximum
effect? Given the range of enhanced conspicuity, which flashing rates align
with various traffic control devices?
4. LED
pitch (spacing): LED’s are placed within a sign legend to depict the letter
stroke width and size of letter. What LED pitch or spacing should be used to
display sign legend and provide maximum sign legibility consistent with MUTCD
legends, text and symbols? Can standard CMS font forms matching the standard
highway fonts be created to improve uniformity?
5. Sign
Shape: The shape of a regulatory and warning sign have been a basic sign design
principle since the 1930’s. The shape provide the road user advance
identification of the sign application prior to legibility of the sign legend.
LED’s are used in the border of signs to enhance their conspicuity. Placing
excessive LEDs on the border can “glare out” driver perspective of sign shape
and legend. What spacing of LED’s in the border are needed to identify the sign
shape for the various regulatory and warning signs and provide enhance
conspicuity?
6. LED
Size: The LED size recommended for sign enhancement and legend has been limited
at ¼ inch. Larger LED’s are available in a variety of types, sizes, colors,
illumination intensity and side fire LED’s.
What are the recommended LED size for regulatory and warning sign
applications that provide the best sign conspicuity while preserving sign
legibility? Does the size of LED, dimming or the intensity of display impact
glare and road user/automated vehicle recognition of traffic control device
function?
7. LED
Sign Size: The LED applications for sign legends increases the sign legibility
beyond static retro-reflective sign legends. Does the use of LED’s in sign
legends permit smaller sign sizes for the some roadway applications?
The research is proposed in two phases. Phase I
will review and update the information on LED usage for regulatory and warning
sign applications. Phase I will also assess the LED technology available for
sign applications and develop appropriate research studies to address the above
seven issues plus any additional identified research. Phase II will conduct the
research with a final report that will document the research studies and
recommend LED applications for regulatory and warning signs.
Accomplishment
of the project objectives will require at least the following tasks.
TASKS
Phase I
Task 1 – Conduct a literature search for any
documents pertaining to the above issues.
Task 2 – Investigate current state of the
practice related to DOT/transportation agency equipment acquisition involving
LEDs. Review manufacturers products to assess the current technology and sign
applications. Survey specifications
related to each of the research issues.
Task 3 – Create research work plans that
provide data-driven resolution to each of the seven issues/questions. Develop
research plan for the issues and budgets for each issue.
Task 4 – Submit an Interim Report for Tasks 1
through 3.
Task 5 – Meet with Research Panel to review the
Interim Report and obtain approval of the research plan.
Phase II
Task 6 – Conduct research studies which provide
data and support to determine optimal LED specifications which address road
user comprehension, uniformity and automated vehicle detection.
Task 7 – Develop recommendations based on the
research to address the issues identified. Recommendations would include
guidelines which would be considered for incorporation in the MUTCD. Identify
potential solutions which may include physical, electronic, or operational
changes to traffic control devices, vehicle image capture and image processing
systems, or both that meet the needs of both human drivers and automated
driving systems.
Task 8 – Submit a Final Report documenting the
entire research.
Urgency And Potential
Benefits
Automated vehicles are increasingly becoming a
part of the vehicle fleet. Electronic traffic control devices are expensive and
have long service lives (over 20 years). Once a CMS or signal is built with LED
specifications that ignore the consequences of uniformity and detection, it
results in greater potential for negative safety consequences and undue
expensive legacy equipment replacement costs.
Any delay in the research will result in the use of non-uniform traffic
control devices at great cost to the public that have the potential for
significant safety implications (ie. dark signals to automated vehicles) and do
not have the best interests of the road user before the convenience and
discretion of manufacturers.
Implementation
Considerations
The prompt completion of this research will
provide the answers that can be incorporated in the Manual on Uniform Traffic
Control Devices (MUTCD) allowing for rapid incorporation by State DOTs and
transportation agencies across the United States to improve long term safety to
road users. This research should include panel members from the National
Committee on Uniform Traffic Control Devices who develop recommended MUTCD
provisions for consideration by the Federal Highway Administration.
Due to the nature of the topic and because this
research will benefit not only state DOTs but also the traffic control device
and automotive industries, a significant number of organizations will be
interested in the research results and could help support implementation
● AASHTO
Committee on Traffic Engineering (CTE)
● AASHTO
Committee on Transportation System Operations (CTSO)
● American
Traffic Safety Services Association (ATSSA)
● Illuminating
Engineering Society of North America (IESNA)
● International Commission on
Illumination (CIE)
● International
Municipal Signal Association (IMSA)
● Institute
of Transportation Engineers (ITE)
● National
Committee on Uniform Traffic Control Devices
● National
Electrical Manufacturers Association (NEMA)
● Society
of Automotive Engineers (SAE)
● USDOT,
Federal Highway Administration
● USDOT,
National Highway Traffic Safety Administration
● American
Society for Testing and Materials (ASTM)
Recommended Research
Funding and Research Period
Recommended Funding: $500,000
Research Period: 30 Months
Problem Statement
Author(S):
For each author, provide their name, affiliation, email address and phone.
James L. Pline, P.E.,PTOE; President, Pline
Engineering Inc., 2520 N. Fry Circle, Boise, ID, 83704, jplineinc@aol.com
, Chair, LED Task Force , Regulatory and
Warning Sign TechnicalCommittee, NCUTCD
Randy McCourt, PE, PTOE, retired, ITE Past President, 6528 SW
Alden Street, Portland, OR 97223, 503.randy.mccourt@gmail.com.
Potential Panel Members: For each panel
member, provide their name, affiliation, email address and phone.
Tom Heydel, WisDOT
Bill Lambert, New Hampshire DOT
Person Submitting The
Problem Statement:
Name, affiliation, email address and phone.
Regulatory and Warning Signs Technical
Committee & Research Committee of
NCUTCD.