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Frequently Asked Questions
- Part 4 Highway Traffic Signals
The following list of questions relates to the MUTCD Part 4 Highway
Traffic Signals:
- How many signalized intersections are there in the
U.S.?
- Why did red and green get selected as the signal
colors to mean "stop" and "go"?
- Why is red in the top position of the signal and green
in the bottom?
- Where did the numbers come from for the vehicular
volume signal warrants in the MUTCD?
- Why does the MUTCD allow the signal warrant volumes
to be reduced to 70 percent of the normal values in certain conditions?
- Where did the numbers for the Pedestrian Volume and
School Crossing signal warrants come from?
- Some agencies' policy is that, whenever one or more
of the numerical signal warrants are met, a signal will be installed.
Doesn't the MUTCD say that other factors beyond just the warrants
have to be considered in the decision to install a signal?
- If none of the numerical signal warrants are met at
an intersection, is there ever any justification for installing a
signal anyway?
- With the increase in traffic volumes, the signal warrants
are being met more frequently. Is the FHWA considering an increase
in volume levels for traffic signal warrants?
- Why was a 56% column added to Table 4C-1, and will
that make it more or less difficult to install a signal?
- Should right-turn traffic from minor streets be counted
in the traffic volume for signal warrant studies, or should it be
disregarded?
- How can I obtain the formulas on which the curves
in the graphs for signal warrants 2 (four-hour warrant) and 3 (peak
hour warrant) are based?
- When analyzing the signal warrants, must the individual
hourly volumes be for hours that all start "on the hour"
(i.e., 6-7 am, 7-8 am, etc.)?
- Warrant #3 (Peak Hour Warrant) requires the use of
data on "vehicle-hours of delay." How is this data measured
and collected?
- Does the MUTCD allow changing from a stop-and-go
signal operation to a flashing mode during low volume periods?
- The MUTCD specifies that the duration of the yellow
change interval should be between 3 and 6 seconds. How is the actual
length determined for a given intersection?
- What is the difference between priority control and
preemption control, such as for emergency vehicles?
- Are traffic signal indications using light emitting
diodes (LEDs) in conformance with the MUTCD?
- Are there maintenance issues associated with LED-based
signals?
- Why was the previous MUTCD guidance that recommended
yellow signal head housings eliminated?
- Are strobe lights allowed in red signals?
- I've invented a new type of signal device that gives
an "early warning" of the impending signal change from green
to yellow by flashing the green for a few seconds before yellow or
by "counting down" the number of seconds until the yellow
comes on. Will FHWA adopt my great new safety idea into the MUTCD?
- How do the standards for traffic signals accommodate
the needs of color-vision deficient drivers? Would it be better to
add shapes to the signal indications to help the colorblind identify
what signal is on?
- My State has many "protected only" mode
left turn signal faces that have a circular red (rather than a red
arrow), a yellow arrow, and a green arrow. Can the R3-5L sign (mandatory
movement left turn only sign) or the R10-5 (LEFT ON GREEN ARROW ONLY)
sign be used alongside this signal face to identify it as a left turn
signal?
- FHWA's Highway Design Handbook for Older Drivers
and Pedestrians recommends that red arrows should not be used
for left turn signals. Why does the MUTCD continue to allow red arrows?
- The 2000 MUTCD changed the meaning of a right turn
red arrow signal by prohibiting right turns on a red arrow after stopping
unless there is a sign specifically allowing it. Then, in the 2003
MUTCD, the R10-17a (Right on Red Arrow After Stop) sign was added
to go along with this. In my State, turning right on a red arrow after
stopping is legal. Why was the MUTCD changed?
- What is the "yellow trap" and why is it
a safety issue?
- Is it correct to assume that there is no need to
be concerned about the "yellow trap" on an intersection
approach where there is no separate left turn phase (that is, the
left turn mode on that approach is "permissive only")?
- Does the MUTCD permit agencies to provide a flashing
amber indication for a left-turn movement for the permissive left-turn
phase?
- When did separate Walk and Don't Walk signals for
pedestrians come into use, and why were those words chosen?
- Pedestrians don't seem to understand the meaning
of the flashing orange hand. Would a "Don't Start" word
legend or a different color work better as a pedestrian change interval
display?
- What is the compliance date for the use of symbols
in existing installations of pedestrian signal heads?
- After calculating the required pedestrian clearance
time, is that the duration of the flashing orange upraised hand interval
that gets set on the signal controller?
- If I choose to use the yellow vehicle change interval
time to satisfy part of the calculated pedestrian clearance time,
does the flashing orange hand have to continue flashing during the
yellow interval?
- The 2003 MUTCD now allows pedestrian countdown signals
to be used. However, it only allows the pedestrian countdown to be
displayed during the pedestrian change interval (flashing orange upraised
hand symbol). Why can't it be displayed during the Walk (white walking
person symbol) interval?
- Studies I've seen on pedestrian countdowns seem to
indicate that they can induce more pedestrians to leave the curb and
start their crossing during the flashing orange hand pedestrian change
interval. Is the countdown encouraging pedestrians to violate the
legal meaning of the flashing orange hand?
- When pedestrian countdowns are used with accessible
pedestrian signals (APS), should there be an audible countdown provided
for vision-impaired pedestrians?
- Will accessible pedestrian signals eventually become
mandatory?
- Does the MUTCD allow the use of a "Leading Pedestrian
Interval"?
- Is there any guidance on bicycle or equestrian signals,
such as design and functional requirements?
- What is the appropriate color of In-Roadway Warning
Lights used with crosswalks? Section 4L.02 indicates yellow but the
color of crosswalk lines is white. Why isn't the color of the In-Roadway
Warning Lights the same color as the crosswalk lines?
- Are In-Roadway Warning Lights allowed for crosswalks
or stop lines at signalized intersections or roundabouts?
- Is any guidance provided in the MUTCD for the flashing
rate of In-Roadway Warning Lights?
- Can in-roadway lights be used to provide brightly
visible guidelines for turning vehicles through an intersection, such
as at a single-point urban interchange (SPUI)?
Part 4 Highway Traffic Signals: Frequently Asked
Questions
- Q: How many signalized intersections are
there in the U.S.?
A: No one can say for sure, because no one collects
comprehensive data on this. A 2004 Institute of Transportation Engineers
(ITE) project, "Signal Timing Practices and Procedures: State
of the Practice", included a survey of a large number of jurisdictions
of all sizes, to estimate the total number of signalized intersections
in the U.S. That report concluded that a very accurate "rule
of thumb" is one signalized intersection per 1,000 population.
That would mean that, as we approach a population of 300 million,
we're approaching 300,000 signals in the U.S.
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- Q: Why did red and green get
selected as the signal colors to mean "stop" and "go"?
A: One of the best references on questions about
the history of traffic control devices such as traffic signals is
a 1971 ITE publication entitled "Traffic Devices---Historical
Aspects Thereof." To summarize information from that publication:
Traffic signals descended from the "semaphores" used by
the railroads. The earliest train tracks were laid in the horse-and-wagon
roads of England. The laws of England required the locomotives to
be accompanied by a flagman who walked in front of the train to warn
other vehicles and horses, and the flagman was required to carry red
flags and red lanterns for this purpose. Red was a color associated
with "danger." (This may be associated with red being the
color of blood.) After the tracks were taken off the roads in England
and put on separate alignments, the railroads developed systems of
semaphores to give directions of stop, go, or proceed with caution
to train engineers. The earliest semaphores often used either red
letters or a red background on the semaphore arm that conveyed the
"stop" message. When lights or lanterns were added to the
semaphores to make them more visible, red was the natural choice for
stop. In the U.S., red kerosene lanterns were used to mark holes or
obstructions in the road, again signifying "danger." The
first traffic signals typically used only two colors, red and green,
although there were some cities that used green to mean east-west
traffic goes and yellow for north-south traffic goes, etc. It was
apparently very confusing, and eventually consensus developed to use
red for stop and green for go, regardless of direction of travel.
By the time a third lens was added to traffic signals to denote the
change interval, yellow had come to be associated with "caution"
via its use on warning signs.
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- Q: Why is red in the top position
of the signal and green in the bottom?
A: Some of the earliest signals used only one set
of two light bulbs to illuminate all the lenses for all four directions.
So, for example, the sides of the signal that faced north and south
would have the red lens on top and the green lens on the bottom, while
the sides that faced east and west would have the green lens on top
and the red on the bottom. In 1927, a committee of municipal officials
(the American Society for Municipal Improvements) recommended that
color and lens position should be standardized to eliminate confusion
and make it possible for people traveling from one city to another
to know what to expect. That committee came to the agreement that
red would be on top and green would be on the bottom and, when used,
yellow would be in the middle. These requirements appeared in the
1930 "urban MUTCD". It's not documented why, but most likely
the red was put on top because the stop message is more important
than the go message and because the top position conveys highest priority
and is more visible above the tops of other vehicles ahead, by virtue
of being higher up over the sidewalk or road.
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- Q: Where did the numbers come
from for the vehicular volume signal warrants in the MUTCD?
A: Vehicular volume warrants for traffic signals
have been in the MUTCD since the earliest editions in the 1930's.
Changes in those warrants have been occurring almost continuously
with each new edition. The original signal warrants came mostly from
a consensus of practicing traffic engineers in the late 1920's as
to what volume conditions seemed to result in improved safety and
efficiency with signalization. Until the 1970's, changes in the warrants
also reflected only engineering consensus and, as far as is known,
were not based on any research. The first warrant changes that had
any research basis were the 4-hour and Peak Hour warrants that first
entered the MUTCD in the 1978 edition. The graphs in the 1978 MUTCD
for the 4-hour and Peak Hour warrants were derived mostly from a very
complicated study done for NCHRP in 1976 by KLD Associates, Inc.,
which evaluated the warrants then in effect and developed additional
"new" warrants by utilizing network simulation models.
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- Q: Why does the MUTCD allow the
signal warrant volumes to be reduced to 70 percent of the normal values
in certain conditions?
A: The KLD NCHRP study report from 1976 indicates
that the 70% factor emerged in the late 50's (when the 1961 MUTCD
was being written) as a "compromise" between rural and urban
traffic engineers then on the NCUTCD. In prior editions of the MUTCD
(1948 and earlier) there had been separate urban and rural warrant
numbers, and the NCUTCD was trying to revise and consolidate them
into a single set of numbers applicable for all conditions. Rural
interests (predominantly the State highway departments) favored lower
warrant numbers so that they could justify signals at rural intersections
and in the downtowns of the small rural communities, both of which
typically exhibited lower volumes than in the cities. The urban interests
felt that the higher (100%) numbers should be retained because with
lower warrant values the number of signals they would have to install
in the rapidly developing cities would greatly increase. Citing conversations
with many "old-timer" NCUTCD members at that time, the KLD
report states that the 70% reduction for speeds over 40 mph and in
the built-up areas of isolated rural communities under 10,000 population
was a "compromise of differing views" between the states
and cities---but there was no research to validate that 70%. The language
in the 1961 and 1971 MUTCDs even indicates that the 70% factor is
"in recognition of differences in the nature and operational
characteristics of traffic in urban and rural environments and smaller
municipalities." (This "explanation" was dropped in
the 1978 and subsequent editions.).
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- Q: Where did the numbers for
the Pedestrian Volume and School Crossing signal warrants come from?
A: A Pedestrian Volume warrant (currently Warrant
4), has been in the MUTCD since the 1935 edition. The numbers in the
original pedestrian volume warrant were not based on any research;
they were the consensus of practicing traffic engineers at that time.
However, in the 1980's the prevailing view was that the numbers were
unrealistically high and too difficult to meet. Two research studies
were done to try to develop new pedestrian volume warrant numbers:
1) Candidate Signal Warrants from Gap Data, February 1983, Report
No. FHWA/RD-82/152; and 2) Pedestrian Signalization Alternatives,
July 1985, Report No. FHWA/RD-83/102. As a result of these studies,
in 1988 the MUTCD was changed, and those numbers for the pedestrian
volume warrant have remained the same since then. The School Crossing
warrant (currently Warrant 5), was added to the MUTCD in 1971. No
information is available on how that warrant was developed or what
it was based on, although there may have been some supporting research
in the late 60s or 1970.
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- Q: Some agencies' policy is that,
whenever one or more of the numerical signal warrants are met, a signal
will be installed. Doesn't the MUTCD say that other factors beyond
just the warrants have to be considered in the decision to install
a signal?
A: Yes, other factors must be considered. The MUTCD
text in Section 4C.01 says "The satisfaction of a traffic signal
warrant or warrants shall not in itself require the installation of
a traffic control signal." It also says that an engineering study
shall be done, and that the study shall include an analysis of those
warrants "and other factors related to existing operation and
safety" at the study location. Basically, the warrants are a
starting point for the analysis leading to determination of justification
for a signal, but engineering judgment must always be applied to assess
all pertinent information in making the decision whether to signalize
or not.
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- Q: If none of the numerical signal
warrants are met at an intersection, is there ever any justification
for installing a signal anyway?
A: In the vast majority of cases, a signal should
not be installed if the MUTCD signal warrants are not met. However,
there can be very rare cases where the engineer's study finds no satisfaction
of numerical warrants but finds other special conditions that cause
him/her to conclude that a signal is the best solution (vs. other
possible alternatives). An experienced and properly qualified traffic
engineer has the ability to assess conditions and make this kind of
a determination under the provisions of the MUTCD. Section 4C.01 says
a signal should not be installed unless one or more of the warrants
are satisfied. That's a "should not" rather than a "shall
not", for the very reason discussed above. The decision and the
engineering reasons for it should be clearly documented in the study.
It is important to note that a politically dictated unwarranted signal
installation (typically against the professional advice of the traffic
engineer) is not what is contemplated by the MUTCD language.
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- Q: With the increase in traffic
volumes, the signal warrants are being met more frequently. Is the
FHWA considering an increase in volume levels for traffic signal warrants?
A: No, the FHWA is not currently considering an
increase in volume levels for traffic signal warrants. However, we
are monitoring ongoing studies that are evaluating potential revisions
in the methodologies and criteria for the Crash Experience Warrant
(#7) and Pedestrian Volume Warrant (#4).
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- Q: Why was a 56% column added
to Table 4C-1, and will that make it more or less difficult to install
a signal?
A: In the 1988 and previous MUTCDs, the 56% factor
was neither explicitly allowed nor prohibited in the signal warrants.
But many jurisdictions inferred that, when applying what used to be
called the Combination Warrant (which allows a reduction to 80%) in
high-speed or isolated rural community conditions (where a reduction
to 70% is allowed), 70% of 80% (56%) could be used. When the warrants
were in a narrative, rather than tabular, form it was possible for
agencies to infer this. In the 2000 MUTCD, when the warrant values
were put into tabular form, the NCUTCD consciously recommended (and
FHWA decided) to not include a 56% column. Subsequently, there were
objections from many agencies that had installed significant numbers
of signals based on meeting the 56% volumes and now those signals
were technically not compliant with the MUTCD. The 2003 edition of
the MUTCD added a 56% column and described the conditions under which
it may be used. This does make it easier to meet the numerical signal
warrants in some conditions. However, because it is an OPTION, jurisdictions
have the ability to decide whether or not this option will be used.
Also, satisfying the numerical warrants does not mean that a signal
must be installed.
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- Q: Should right-turn traffic
from minor streets be counted in the traffic volume for signal warrant
studies, or should it be disregarded?
A: In Section 4C.01, the MUTCD states, "Guidance:
The study [engineering study] should consider the effects of the right-turn
vehicles from the minor-street approaches. Engineering judgment should
be used to determine what, if any, portion of the right-turn traffic
is subtracted from the minor-street traffic count when evaluating
the count against the above signal warrants." Section 4C.01 also
includes additional guidance concerning the presence of an exclusive
right-turn lane and how that might impact how much of the right turn
volume is included. Please refer to that section for more detail on
this issue.
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- Q: How can I obtain the formulas
on which the curves in the graphs for signal warrants 2 (four-hour
warrant) and 3 (peak hour warrant) are based?
A: The formulas are not readily available. Those
graphical MUTCD signal warrants were based (loosely) on modeling and
simulation research in the 1970's that developed a large number of
curves. The curves that ended up in the MUTCD don't exactly match
what's in the research report, as a result of massaging that was done
to obtain consensus agreement on the new warrants from the practicing
traffic engineering community at that time. The developers of commercial
software products that "automate" the signal warrant analysis
process most likely created formulas or equations by working backwards
from plotted points on the curves and/or using "curve fitting"
programs. Also, the HTML version of Part 4 on FHWA's MUTCD website
has tabular formatted charts of the graphs that are part of the Section
508-compliant "text descriptions" of the figures and graphics.
Those descriptions were developed specifically to meet Section 508
of the ADA law, which requires the federal government to make accessible
to blind and visually-impaired persons any material that is posted
in electronic format on websites. The firm that developed the descriptions
for FHWA did what anyone could have done---plot values of some points
on the curves and put them into tabular form that a visually disabled
person's HTML-reader software can read. However, it must be recognized
that these plotted point numerical values have no official or legal
basis and are just estimates provided for user information only. A
direct link to the HTML version of Chapter 4C is:
http://mutcd.fhwa.dot.gov/HTM/2003/part4/part4c.htm.
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- Q: When analyzing the signal
warrants, must the individual hourly volumes be for hours that all
start "on the hour" (i.e., 6-7 am, 7-8 am, etc.)?
A: There is nothing in the MUTCD text that requires
the hours being analyzed to start on the hour. Many agencies' traffic
counts are tabulated with 15-minute subtotals and it has been very
common longstanding practice for signal warrant analyses to evaluate
not just the 1-hour periods that start "on the hour" at
:00 but also those that start at :15, :30, etc. This is because the
peak traffic hours can occur any time, often resulting from school
start/end times, factory or shopping mall open/close times, etc. The
one-hour periods need not be consecutive. They can be any one-hour
periods that do not overlap each other. For example, the 3 highest
non-overlapping hours in the AM peak might be 6:15 to 7:15, 7:30 to
8:30, and 8:45 to 9:45. However, whatever hours are selected must
be used to evaluate warrant satisfaction for both the major road volume
and the minor road volume in those specific hours.
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- Q: Warrant #3 (Peak Hour Warrant)
requires the use of data on "vehicle-hours of delay." How
is this data measured and collected?
A: In the peak hour, the number of vehicles on the
approach must be counted and either the average delay per vehicle,
or the total delay encountered by all the vehicles on that approach
during that peak hour, must be measured (typically with a stopwatch)
and recorded. If there is, for example, a volume of 300 vehicles on
the minor street approach during the peak one hour, and the average
delay per vehicle on that approach during that peak hour is 60 seconds
per vehicle, then there would be 300 x 60 or 18,000 vehicle-seconds
of delay. Since there are 3600 seconds in one hour, 18,000 vehicle-seconds
equates to 5.0 vehicle-hours of delay.
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- Q: Does the MUTCD allow changing
from a stop-and-go signal operation to a flashing mode during low
volume periods?
A: Yes, but specific guidance is not given in the
MUTCD on thresholds for such changes, which should be based on an
engineering study or engineering judgment. Section 4D.11, Application
of Flashing Signal Indications, and Section 4D.12, Flashing Operation
of Traffic Control Signals, discuss flash rate, the flashing indications,
the colors allowed to flash on which movements' displays, and how
flashing mode is initiated and terminated.
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- Q: The MUTCD specifies that
the duration of the yellow change interval should be between 3 and
6 seconds. How is the actual length determined for a given intersection?
A: Within this 3 to 6 second range recommended by
Section 4D.10 of the MUTCD, jurisdictions are free to set yellow change
interval timing based on their own policies or studies. ITE has published
guidelines for determining the length of yellow and all-red intervals.
(Visit ITE's website at www.ite.org
where you will find additional information under "Technical Information".)
Those ITE guidelines utilize scientifically derived formulas based
on engineering principles and years of research. The yellow change
interval is calculated based on speed of approaching vehicles, the
stopping ability of approaching vehicles, and the width of the intersection.
The ITE guidelines are used by many jurisdictions as the basis of
either the overall policies or the individual intersection timings
for yellow change intervals. Because vehicle laws vary by State and
conditions vary by intersection, the engineer must exercise judgment
in deciding on the length of the yellow interval.
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- Q: What is the difference between
priority control and preemption control, such as for emergency vehicles?
A: Section 4D.13 provides standards, guidance and
options for the preemption and priority control of traffic control
signals. Priority control can be given to certain non-emergency vehicles
such as buses and light-rail vehicles. It is typically less disruptive
to normal signal operations, and most normal rules for signal sequences
and timing apply. Preemption control can disrupt normal operations
and institute special signal phases, and shortening or omission of
certain normally-required intervals is permitted. When preemption
occurs, it may take several signal cycles to resume normal operation
in a coordinated signal system. Therefore, preemption control typically
is given only to emergency vehicles and to vehicles that cannot be
easily stopped, such as boats (at drawbridges) and trains (at or near
railroad crossings).
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- Q: Are traffic signal indications
using light emitting diodes (LEDs) in conformance with the MUTCD?
A: Yes, as long as they comply with the applicable
ITE standards. The MUTCD does not specify the type of light source
used for traffic control signal indications. Section 4D.18 states,
"Support: Research has resulted in signal optical units that
are not lenses, such as, but not limited to, light-emitting diode
(LED) traffic signal modules." It also states, "Standard:
References to signal lenses in this section shall not be used to limit
signal optical units to incandescent lamps within optical assemblies
that include lenses." However, Section 4D.18 also requires the
design, illumination, and color all signal indications, including
those using LEDs, to meet the requirements of the "Standards
for Vehicle Traffic Control Signal Heads" published by the Institute
of Transportation Engineers (ITE). The intensity and distribution
of light from each illuminated signal lens should also conform to
the ITE standards. ITE updated those standards in 2005 (information
available at http://www.ite.org/standards/led.asp).
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- Q: Are there maintenance issues
associated with LED-based signals?
A: Agencies using LED-based signals should be aware
that these signals need to be monitored for adequate brightness of
the signals and for needed replacement, typically well before the
signals fail totally. LEDs have a long life before total failure,
but the LEDs gradually become dimmer over time and may become so dim
that they cannot be adequately seen under all lighting conditions.
This is in contrast to signals using incandescent bulbs, which usually
remain sufficiently bright over their full lifetime and then fail
completely by "burning out". Agencies thus quickly become
aware of and replace failed incandescent signals. Agencies need a
different strategy for monitoring and replacing LED signals.
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- Q: Why was the previous MUTCD
guidance that recommended yellow signal head housings eliminated?
A: The 1988 and prior editions of the MUTCD stated
that "it is desirable that signal head housings be yellow."
This language was not a strong recommendation and, as such, was not
a uniform practice by many agencies. In the 2000 MUTCD, with reformatting
of all text into standards, guidance, options, and support, this became
a Guidance statement that "to obtain the best possible contrast
with the visual background, signal housings should be highway yellow."
This guidance was deleted effective with the 2003 edition, because
there is no consensus that yellow signal housings universally provide
the best contrast in all of the various environments. In actual practice,
it is estimated that far fewer than 50 percent of the signal heads
in the United States are highway yellow. California, New York State,
and many other jurisdictions with very large numbers of signals require
their signal heads to be other colors, such as green, black, gray,
brown, etc. Regardless of the color of the signal housings, it is
important to assure that the signal indications are adequately visible
and in contrast to their backgrounds by applying the MUTCD standards
and guidance on design aspects such as signal head placement, signal
lens size, use of backplates, etc.
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- Q: Are strobe lights allowed
in red signals?
A: No, they are not allowed. There are no provisions
in Part 4 of the MUTCD that allow the use of strobes within red traffic
signals. Section 4D.18 requires the design, illumination, and color
all signal indications, including those using LEDs, to meet the requirements
of the "Standards for Vehicle Traffic Control Signal Heads"
published by the Institute of Transportation Engineers (ITE), and
those standards do not provide for strobes as part of the design.
Research and experimentation over the years with white strobe lights
as a circular "halo" outer ring around the red signal or
as horizontal bar across the red signal has found no lasting safety
benefit and, in some cases, the strobes resulted in increased crash
frequency. Based on this experience, FHWA made a determination in
1990 no further experimentation with strobe lights in traffic signals
would be approved and that all existing strobes were to be removed.
In 1995 a report by the Virginia Transportation Research Council provided
an updated review of strobe light effectiveness in the States where
they had been used. That report validated the previous analyses and
came to the same basic conclusion, that there is no evidence that
strobe lights are consistently effective in reducing crashes. Therefore,
it is still FHWA's position that strobe lights are not allowed in
traffic signals and no further experimentations with these types of
strobe lights in traffic signals will be approved. This position was
formalized in July 2003 with an Official Interpretation of the MUTCD,
number 4-263(I).
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- Q: I've invented a new type
of signal device that gives an "early warning" of the impending
signal change from green to yellow by flashing the green for a few
seconds before yellow or by "counting down" the number of
seconds until the yellow comes on. Will FHWA adopt my great new safety
idea into the MUTCD?
A: There has been considerable experience with ideas
intended to provide an advance signal indication of the change from
green to yellow. Typically, the ideas have involved flashing the green
for a few seconds before the yellow appears, varieties of displayed
numbers that count down to zero, and sequences of lights being extinguished,
illuminated, or flashed as the change from green to yellow is approaching.
Although well intentioned, these ideas have not proven to be effective;
in fact they have been counter-productive, due to unintended consequences.
Each time displays such as these have been tried, it was found that
they lengthened the "dilemma zone" in which drivers are
unsure whether to stop or proceed, they encouraged more drivers to
unreasonably speed up to "beat the light," and the increased
aggressive driving behavior caused more crashes to occur than was
the case without the advance indication of the change to yellow. Because
research in other countries as well as in the U.S. has conclusively
shown that such displays reduce, rather than improve, highway safety,
FHWA does not believe it is appropriate to allow experimentation or
to consider including any such pre-yellow signal displays for vehicular
traffic control signals in the MUTCD.
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- Q: How do the standards for
traffic signals accommodate the needs of color-vision deficient drivers?
Would it be better to add shapes to the signal indications to help
the colorblind identify what signal is on?
A: Distinguishing reds from greens is by far the
most common problem for color vision deficient people. This has been
taken into account in the MUTCD, which since the 1930s has specified
the relative positions of the different colored signal indications,
with red always being above yellow, which is always above green (in
a vertically-arranged signal.) This positional requirement also applies
to arrow indications, with red arrows always being above yellow arrows,
which are always above green arrows. For horizontally arranged signals,
similar positional requirements are established, with red always being
the left-most indication, etc. It would seem logical that shapes could
potentially provide additional assistance to colorblind road users,
beyond that already provided by the positional standards. However,
a Canadian province that has used such a shape system in its traffic
signals in the past has abandoned it due to lack of effectiveness
and other issues. Changing the shape of the signal indications results
in changes in light output and this impacts how well and how far away
the signals can be seen by drivers, particularly under adverse conditions
such as fog, smoke, dust, visually complex environments, etc. Therefore,
research would be needed to evaluate what changes in signal light
sources and intensity might be necessary if the shapes of the lenses
were to be changed, and also how colored arrow signals could be associated
with shapes. Meanwhile, studies have found that most color blind people
adapt and compensate well by using the positional requirements contained
in the existing traffic signal standards to help them discern the
colors. Also, in the most recent update of the detailed color standards
for traffic signals (published by ITE), the green has been specified
to be a bit more "blue-green" because this makes it easier
for persons with red-green color vision deficiencies to distinguish
it from red.
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- Q: My State has many "protected
only" mode left turn signal faces that have a circular red (rather
than a red arrow), a yellow arrow, and a green arrow. Can the R3-5L
sign (mandatory movement left turn only sign) or the R10-5 (LEFT ON
GREEN ARROW ONLY) sign be used alongside this signal face to identify
it as a left turn signal?
A: No, the R3-5L or R10-5 signs cannot be used for
this purpose. Section 4D.06, in discussing the requirements for signal
displays for "protected only" mode left turns, states that
when a circular red is used instead of a red arrow in a 3-section
left turn signal face for this mode, "Unless the circular red
signal indication is shielded, hooded, louvered, positioned, or designed
such that it is not readily visible to drivers in the through lane(s),
a LEFT TURN SIGNAL sign (R10-10) shall be used." Thus, the R10-10L
is the only sign to be used for this purpose, which is to help prevent
through traffic from mistaking the circular red in the left turn signal
face as applying to the through movement. The R3-5L sign requires
road users in a specific lane to only turn left from that lane and
not make other movements. The R10-5 sign communicates to left turn
drivers about when they are allowed to turn. Neither the R3-5L nor
the R10-5 is intended to convey any message about what the purpose
of the signal face is or what movements must obey that signal face.
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- Q: FHWA's Highway Design
Handbook for Older Drivers and Pedestrians recommends that red
arrows should not be used for left turn signals. Why does the MUTCD
continue to allow red arrows?
A: When the use of red arrows was proposed for elimination
from the MUTCD in the late 1990s, based on the older driver report's
recommendations, some commenters to the docket pointed out problems
with the underlying research. They identified the fact that the older
driver red arrow research was conducted in the 1980s, at a time when
red arrows were relatively new, not in much use yet around the country,
and thus "unfamiliar" to many older drivers. The State of
Florida, which has used red arrows extensively for many years, reported
their very positive experience with red arrows and the preference
among older drivers in Florida for red arrows rather than red balls
for left turn signals. Many commenters noted that a red arrow is a
very valuable tool that provides far better control than a circular
red indication in some geometric situations. These facts led FHWA
to determine that the recommendation to remove red arrows from the
MUTCD was flawed, and that proposal was withdrawn. There is no intention
to remove red arrows from the MUTCD in the future and in fact most
States are now using red arrows.
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- Q: The 2000 MUTCD changed the
meaning of a right turn red arrow signal by prohibiting right turns
on a red arrow after stopping unless there is a sign specifically
allowing it. Then, in the 2003 MUTCD, the R10-17a (Right on Red Arrow
After Stop) sign was added to go along with this. In my State, turning
right on a red arrow after stopping is legal. Why was the MUTCD changed?
A: The R10-17a sign and the revised definition of
the meaning of a red arrow signal stem from a change in the Uniform
Vehicle Code (UVC) that revised the meaning of the red arrow to include
the prohibition of turns on red arrow after stopping unless a sign
specifically permits it. The UVC change came about because of the
lack of uniformity among State laws on this subject. The majority
of States' laws prohibit the turn on red arrow after stopping without
a permissive sign, while the minority of States allow turns on red
arrows after stop unless a sign prohibits it. The UVC, which is written
by a group comprised mostly of State motor vehicle administrators,
adopted the majority practice. The change also took into account that
a key use of red right arrows is with signal phasing that "protects"
the pedestrian crossing from right turn traffic during a "leading
pedestrian interval" by keeping the right turns stopped on a
red arrow, while the parallel thru movement receives a green. Although
this isn't the only use for red right turn arrows, it is one in which
the red arrow is critical. Allowing RTOR on red arrow under this condition
is counter-productive to the purpose of using the red arrow. It was
felt that, at the relatively few red right arrow locations where agencies
might actually want to allow RTOR, this could be accommodated by posting
the sign to specifically allow it there. For reasons of national uniformity,
the MUTCD's text on the meanings of signal indications must match
the UVC.
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- Q: What is the "yellow
trap" and why is it a safety issue?
A: The "yellow trap" is a potentially
adverse safety situation inherent in some signal phasing sequences
involving lagging left turns in one direction. A left turning driver,
in the intersection waiting for gaps in oncoming traffic in order
to turn left on a permissive green signal indication, sees the signals
for adjacent through traffic change from green to yellow and mistakenly
assumes that oncoming through traffic also has yellow signals at the
same time and will be soon coming to a stop. This mistaken assumption
"traps" the permissive left turner into thinking it is OK
to safely complete the turn when in reality it is not safe, because
the opposing traffic continues along with a lagging left turn, and
a severe crash can be the result. Section 4D.05, item B.4 prohibits
the "yellow trap" sequence except in rare and unusual cases
and then only with a W25-1 or W25-2 sign to warn drivers of the condition.
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- Q: Is it correct to assume
that there is no need to be concerned about the "yellow trap"
on an intersection approach where there is no separate left turn phase
(that is, the left turn mode on that approach is "permissive
only")?
A: No, this is not a correct assumption. The prohibition
against "yellow trap" sequences applies to any signalized
location at which any left turn movement can be made on a permissive
basis. An approach that does not have a left turn green arrow but
from which a left turn movement is legal and feasible during the circular
green phase would "trap" left turners on yellow if the opposite
approach has a lagging left turn phase (the opposing green continues.)
Also, with actuated signal operation, phase skipping in the absence
of demand can also result in the yellow trap. This can be avoided
by using the "anti-backup" feature provided by most signal
controller manufacturers.
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- Q: Does the MUTCD permit agencies
to provide a flashing amber indication for a left-turn movement for
the permissive left-turn phase?
A: This display is not allowed by the 2003 MUTCD.
Section 4D.06 requires the display applicable to a left turn lane
that is allowed to turn permissively to be a CIRCULAR GREEN. However,
NCHRP Report 493 describes the results of a comprehensive research
project to evaluate the use of different permissive displays for protected-permissive
mode left turns (PPLT), including the flashing yellow arrow (FYA).
The research found that the most easily understood and most effective
permissive display is the FYA in an all-arrows separate turn signal
face for the left turn. As a part of the NCHRP research project and
as follow-up to it, several dozen jurisdictions have been experimenting
with the FYA for PPLT. Based on experience to date, FHWA anticipates
proposing for the next edition of the MUTCD that the FYA display be
added to Section 4D.06 as an optional alternative for PPLT mode. In
March 2006, the FHWA issued an Interim Approval for the use of FYA
as an optional alternative display for PPLT or "permissive only"
left turn movements. Any jurisdiction that wishes to use FYA under
the Interim Approval must write to FHWA and agree to the conditions.
For more information, see http://mutcd.fhwa.dot.gov/res-interim_approvals.htm.
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- Q: When did separate Walk and
Don't Walk signals for pedestrians come into use, and why were those
words chosen?
A: During the 1930's, city officials were trying
to figure out how to reduce the death and injury toll among pedestrians.
One method was to add a light to the traffic signals to indicate a
walk phase, during which all traffic approaching the intersection
stopped so pedestrians could cross the streets in all directions,
including diagonally. New York, Chicago, and Washington, DC are known
to be early users of this idea. In the 1930's and 1940's the most
typical practice was to add a fourth signal indication below the standard
red-yellow-green vehicular signal, with a white "WALK" on
circular black background. The "WALK" would come on for
an "exclusive" pedestrian phase, and then for the pedestrian
change interval the "WALK" would be extinguished while the
red vehicular signal indications stayed on. The 1935 MUTCD was the
first to discuss pedestrian signal indications, allowing circular
signal lenses with the words WALK and WAIT to be used. The 1948 MUTCD
recommended that pedestrian indications be separately mounted on the
intersection corners and allowed either circular lenses with white
WALK and orange WAIT or rectangular shaped sections with red neon
tubing forming the words WALK and DON'T WALK. A steady WAIT or DON'T
WALK was used for the pedestrian change interval. The addition of
the flashing Don't Walk display for the change interval (starting
as an optional alternative in the 1961 MUTCD) was presumably due to
pedestrian compliance problems with the former practice. The 1961
MUTCD also stated: "Former editions have authorized WAIT as an
alternative to DON'T WALK. WAIT is believed to be less readily understood
by pedestrians and is too easily mistaken for WALK. Therefore WAIT
is deleted as a permissible standard."
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- Q: Pedestrians don't seem to
understand the meaning of the flashing orange hand. Would a "Don't
Start" word legend or a different color work better as a pedestrian
change interval display?
A: Studies have consistently shown that the flashing
orange hand and its predecessor, the flashing word legend "DON'T
WALK", are not well understood by pedestrians. One reason may
be the dual meaning of the indication, depending on whether you are
on the curb (stay on the curb and don't begin to cross) or already
in the crosswalk (continue crossing to the far side or a safety island.)
A variety of research studies have evaluated possible alternatives,
such as WAIT, DON'T START, three-section pedestrian signals with different
colors for the pedestrian change interval, and various combinations
of these. Unfortunately, none of the alternatives have been found
to be significantly superior to the existing. It appears that the
best strategy is to better educate pedestrians as to the meanings
of the existing pedestrian signal indications. Many jurisdictions
have developed educational flyers and website information on this
subject, as well as installing pedestrian educational plaques (R10-3b,
c, d, or e) explaining the meanings adjacent to pedestrian push buttons.
Also, pedestrian countdown displays can help to reduce the occurrence
of pedestrians still in the street at the end of the pedestrian clearance
time.
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- Q: What is the compliance date
for the use of symbols in existing installations of pedestrian signal
heads?
A: The requirement to use symbols for pedestrian
signal indications for new installations first appeared in the 2000
edition of the MUTCD. In the 2003 edition, the requirement for new
installations was further limited to solid symbols rather than outline
style symbols, due to the difficulty that older pedestrians and pedestrians
with visual disabilities experience in seeing the outline symbols.
However, the previously existing word legend and outline symbol pedestrian
signal indications are "grandfathered" and do not have a
specific compliance date for replacement with solid symbols. Section
4E.04 of the 2003 MUTCD states, "Standard: All new pedestrian
signal indications shall be displayed within a rectangular background
and shall consist of symbolized messages, except that existing pedestrian
signal indications with lettered or outline style symbol messages
may be retained for the remainder of their useful service life."
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- Q: After calculating the required
pedestrian clearance time, is that the duration of the flashing orange
upraised hand interval that gets set on the signal controller?
A: It depends---it may be, but it doesn't have to
be. There is a subtle but important difference between "pedestrian
clearance time" and "pedestrian change interval". The
pedestrian clearance time is the calculated number of seconds needed
for pedestrians to cross the distance to the far side of the traveled
way (or median) when walking at a given walking speed (such as 4 feet
per second, or slower if necessary.) Suppose that, based on the assumed
walking speed and the width of road to be crossed, 20 seconds is needed
for the pedestrian clearance time. Section 4E.10 allows the 20 seconds
of pedestrian clearance time to be contained totally within the vehicular
green interval (in which case the 20 seconds is set on the controller
as the pedestrian change interval time), OR it can be split between
the green interval and the yellow interval. In this latter case, if
the yellow change interval is 4 seconds, that 4 seconds would be counted
as part of the 20 seconds and thus 16 seconds would be set on the
controller as the duration of the pedestrian change interval. Including
the yellow time as part of the pedestrian clearance time is typically
considered when significant intersection capacity concerns make it
necessary to keep the green time as short as possible.
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- Q: If I choose to use the yellow
vehicle change interval time to satisfy part of the calculated pedestrian
clearance time, does the flashing orange hand have to continue flashing
during the yellow interval?
A: With most actuated controllers, the orange hand
is flashed only during the time set as the pedestrian change interval
and it would be steady orange hand during the yellow change interval.
However, some jurisdictions set up their controllers to flash the
orange hand all the way through the vehicular yellow interval. This
is allowable under Section 4E.10 but is not required. However, when
(optional) Countdown Pedestrian Signal displays are used with the
pedestrian signals, Sections 4E.07 and 4E.10 now require the end of
the flashing orange hand to occur simultaneously with the end of vehicular
green/start of yellow. So, if countdowns are used, the flashing orange
hand cannot continue through the yellow interval. If no countdowns
are used, the flashing orange hand may continue through the yellow
interval but there is no requirement to do so.
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- Q: The 2003 MUTCD now allows
pedestrian countdown signals to be used. However, it only allows the
pedestrian countdown to be displayed during the pedestrian change
interval (flashing orange upraised hand symbol). Why can't it be displayed
during the Walk (white walking person symbol) interval?
A: The MUTCD specifies that the countdown is not
to start until the start of the flashing orange hand. This is because
in vehicle-actuated systems that use the "rest in walk"
feature with a variable-duration vehicular green phase, it is not
feasible to display a countdown during the Walk interval. While the
vehicular phase is either "resting" (with no vehicles detected
on conflicting phases) or being extended by approaching vehicles,
the parallel concurrent pedestrian phase remains in Walk. In the absence
of a conflicting call, the Walk remains on indefinitely. It is only
after a conflicting phase call is detected that the pedestrian change
interval (flashing orange hand) begins timing. With this "rest-in-walk"
operation, it is not feasible to count down the walk interval. Even
though some jurisdictions do not use "rest in walk" mode,
and some jurisdictions may have virtually all fixed-time signals,
it would be confusing to pedestrians if they encountered different
countdown operations at different intersections, within the same jurisdiction
or as they travel from one jurisdiction to another. The common denominator
workable with all signals, regardless of actuated or fixed time, is
to count down only the pedestrian change interval.
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- Q: Studies I've seen on pedestrian
countdowns seem to indicate that they can induce more pedestrians
to leave the curb and start their crossing during the flashing orange
hand pedestrian change interval. Is the countdown encouraging pedestrians
to violate the legal meaning of the flashing orange hand?
A: Yes, studies have found that the pedestrian countdown
display does result in a larger percentage of pedestrians who start
their crossing during the flashing orange hand. However, the studies
have also found that the countdowns result in a significantly smaller
percentage of pedestrians who have not completed their crossing by
the end of the allocated pedestrian clearance time. The countdown
information is most likely leading pedestrians to speed up their pace
as the numerals decrease toward zero, something that may not occur
at locations without the countdown information. Regarding the legal
meaning of the flashing orange hand, it must be remembered that this
meaning was developed well prior to any consideration of a countdown
display being used. It's also important to note that the duration
of the pedestrian clearance time is based on an assumed walking speed.
Pedestrians who walk faster than that assumed speed often come to
realize that they can leave the curb a few seconds after the flashing
orange hand starts and still make it across in plenty of time, and
the countdown information reinforces that behavior, which is not necessarily
unsafe. Some jurisdictions have enacted ordinances that specifically
make it legal to start crossing during the flashing orange hand at
crossings equipped with countdowns, as long as the pedestrian completes
his or her crossing before conflicting traffic gets a green signal.
Similar changes may need to be considered in the future for the Uniform
Vehicle Code and MUTCD language on meanings of pedestrian indications.
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- Q: When pedestrian countdowns
are used with accessible pedestrian signals (APS), should there be
an audible countdown provided for vision-impaired pedestrians?
A: Some advocates for the visually disabled believe
that the countdown information should also be provided in an accessible
(audible) format. However, there are some significant problems with
providing the countdown information to people with visual disabilities.
The countdown only occurs during the pedestrian change interval (flashing
orange hand), during which pedestrians have already left the corner
and are in the street. The Orientation and Mobility Division of the
Association for Education and Rehabilitation of the Blind and Visually
Impaired has investigated the issue of providing audible pedestrian
change interval signals, including audible countdowns, and has recommended
against them. If the countdown were broadcast in audible format from
the opposite side of the street to ensure those crossing can hear
it to the end of the crossing, then the audible countdown will mask
the other environmental and moving traffic sounds that blind people
need to be able to hear and concentrate on once they have started
their crossing. If the audible countdown were broadcast from the near
side of the street, the sound will fade as the person crosses. Also,
the more audible messages there are at an intersection which already
has APS pushbutton locator tones and tones to signal the Walk interval,
the greater the likelihood that blind pedestrians will confuse one
with the other. The more loud signals there are, the greater the likelihood
that there will be neighborhood objection and/or vandalism.
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- Q: Will accessible pedestrian
signals eventually become mandatory?
A: At this point, it is too early to determine whether
accessible pedestrian signals will become mandatory. As with many
new traffic control devices, the Standards, Guidance, and Options
for their use will most likely evolve as more accessible pedestrian
signals are in use. Also, the U.S. Access Board, part of the U.S.
Department of Justice, the agency that administers the Americans with
Disabilities Act (ADA), plans to initiate a formal rulemaking process
for adopting ADA Accessibility Guidelines for the Public Right-of-Way.
The current draft of those guidelines calls for accessible pedestrian
signals to be required at all intersections equipped with pedestrian
signals and at all pedestrian crossings across multi-lane roundabout
entry or exit roadways, whenever new construction or alterations occur.
If the proposed requirements are retained in the Access Board's final
rule, the MUTCD will have to be revised in the future to reflect those
requirements.
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- Q: Does the MUTCD allow the
use of a "Leading Pedestrian Interval"?
A: This type of sequence has been used for a long
time by a many cities to help pedestrians get a bit of an "edge"
over turning vehicles where an engineering study determines it is
needed, and its use is increasing. It was specifically described in
the 1961, 1971, and 1978 editions of the MUTCD. The 1988 MUTCD eliminated
the narrative descriptions of this and all other types of pedestrian
signal phasing, considering that information more suitable for handbooks.
The Pedestrian User Guide published by FHWA and available on the Walkinginfo.org
web site indicates that studies have found the leading pedestrian
interval (LPI) has reduced conflicts for pedestrians. The LPI is particularly
helpful for older pedestrians who are slower to start into the intersection
than other pedestrians, thus giving better notice of their presence
in the roadway/crosswalk for right turning drivers. The FHWA Older
Driver and Pedestrian Highway Design Handbook recommends the use of
the LPI where older pedestrians use the intersection. Even though
there is currently no specific text in Part 4 of the MUTCD that describes
LPI, a signal sequence that includes LPI is fully compliant as long
as the basic MUTCD principles and rules of signal displays are followed.
It is not experimental and no experimentation request is needed in
order to use it.
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- Q: Is there any guidance on
bicycle or equestrian signals, such as design and functional requirements?
A: Traffic control signals used for bicyclists and
equestrian crossing locations shall conform to Part 4 of the MUTCD
(that is, they must be pedestrian signals per Chapter 4E or vehicular
signals per Chapter 4D.) There are no special signal indications for
bicycles or equestrians in the MUTCD at present. A few jurisdictions
have received FHWA experimentation approval for use of bicycle signal
indications. These are bicycle-shaped red, yellow, and green symbols
on opaque backgrounds. Any other jurisdictions wishing to use bicycle
signal indications, or equestrian signal indications, must request
experimentation approval.
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- Q: What is the appropriate
color of In-Roadway Warning Lights used with crosswalks? Section 4L.02
indicates yellow but the color of crosswalk lines is white. Why isn't
the color of the In-Roadway Warning Lights the same color as the crosswalk
lines?
A: Section 4L.02 states that In-Roadway Warning
Lights at crosswalks shall display a flashing yellow indication when
actuated. Since this is a warning device intended to alert road users
to exercise special caution, similar to a flashing beacon, the color
yellow is specified to provide a distinct warning message that gets
the attention of road users in advance of the actual crosswalk.
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- Q: Are In-Roadway Warning Lights
allowed for crosswalks or stop lines at signalized intersections or
roundabouts?
A: They are allowed for crosswalks at roundabouts
but not allowed for crosswalks or stop lines at signalized intersections.
Typical modern roundabout design calls for the crosswalks to be located
25 to 40 feet in advance of where the entering roadway traffic must
yield to the circulatory roadway traffic. Those crosswalks are thus
considered an uncontrolled location and thereby eligible for the use
of In-Roadway Warning Lights (IRWLs). Use at signalized intersections
is not allowed because Section 4L.02 states that IRWLs "shall
not be used at crosswalks controlled by YIELD signs, STOP signs, or
traffic control signals." A few jurisdictions have obtained FHWA
approval to experiment with red in-roadway warning lights that are
illuminated when the red signal is on, to supplement stop lines at
signalized intersections. Other jurisdictions wishing to use in-roadway
lights in applications other than that described in Section 4L.02
must request experimentation approval.
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- Q: Is any guidance provided
in the MUTCD for the flashing rate of In-Roadway Warning Lights?
A: Section 4L.02 states that the flash rate for
In-Roadway Warning Lights at crosswalks shall be at least 50, but
not more than 60 flash periods per minute. This standard is modified
by the option in Section 4L.01 that allows In-Roadway Warning Lights
to have a flash rate different from the flash rate of standard beacons.
Some varieties of In-Roadway Warning Lights use a "stutter flash"
that rapidly pulses the lights during the "on" portion of
their on-off cycle. Section 4L.02 further states that the flash rate
shall not be between 5 and 30 flashes per second, to avoid frequencies
that might cause seizures. Thus, the pulsing during the "on"
periods of the light must be at a rate slower than 5 per second or
faster than 30 per second.
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- Q: Can in-roadway lights be
used to provide brightly visible guidelines for turning vehicles through
an intersection, such as at a single-point urban interchange (SPUI)?
A: A distinction must be made between "internally
illuminated raised pavement markers" (IIRPMs), which are regulated
by Sections 3B.11 through 3B.14), and "in-roadway warning lights"
(IRWLs), which are regulated by Sections 4L.01 and 4L.02. IIRPMs can
be used to provide the same functions as retroreflective RPMs, such
as supplementing normal longitudinal pavement marking lines. IIRPMs
can be illuminated by incandescent, LED, or other light sources, but
they must be steadily illuminated and not flashed. IIRPMs have been
used in accordance with Part 3 standards to supplement dotted line
extensions for turning movements through intersections or interchanges.
In-roadway lights that are flashed intermittently have been determined
to be IRWLs, which Chapter 4L requires to be yellow in color because
they provide the same function as a traditional flashing beacon. IRWLs
are limited in application by the current MUTCD to uncontrolled crosswalks.
However, some jurisdictions have requested and received FHWA approval
for experimentations to evaluate the use of flashing IRWLs of other
colors and for other uses.
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