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?
Should right-turn traffic from minor streets be counted in the traffic volume for signal warrant studies, or should it be disregarded?
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.)?
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?
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?
Why was a 56% column added to Table 4C-1, and will that make it more or less difficult to install a signal?
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?
Warrant #3 (Peak Hour Warrant) requires the use of data on "vehicle-hours of delay." How is this data measured and collected?
Where did the numbers for the Pedestrian Volume and School Crossing signal warrants come from?
Sections 4D.01 and 4D.32 of the 2009 MUTCD refer to "covering" of signal faces as one of the acceptable methods for indicating a signal is not in operation. In my jurisdiction, yellow retroreflective borders are used on the signal backplates of some signal faces. If such a face is to be covered, are there any specific requirements about covering the yellow retroreflective backplate borders?
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")?
Where the cross street is one-way, can a vertical green arrow indication be substituted for circular green, to emphasize that wrong-way turns are not allowed into that one-way cross street?
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?
Are strobe lights allowed in red signals?
Are traffic signal indications using light emitting diodes (LEDs) in conformance with the MUTCD?
Are there maintenance issues associated with LED-based signals?
Do the Institute of Transportation Engineers (ITE) Vehicle Traffic Control Signal Heads standards include the new U-turn arrow signal indications?
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?
Why was the previous MUTCD guidance that recommended yellow signal head housings eliminated?
Why does the 2009 MUTCD recommend against locating a signal face that displays a circular green indication above or in front of an exclusive left turn lane?
My agency prefers to have a signal face over each lane on the approach, including left turn lanes that are operated as "permissive-protected" or "permissive only" mode left turns. Is there a way to do that without violating paragraph 09 of Section 4D.13?
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 2009 MUTCD now require red arrows in protected-only mode left turn signals?
My State still 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. Until we replace the circular reds with red left arrows, 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?
Does the MUTCD now require agencies to provide a flashing yellow arrow indication for a left-turn movement for the permissive left-turn phase?
What sign should be used to explain to drivers what flashing yellow arrow means?
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?
Are the ITE formulas the only "engineering practices" that can be used to determine duration of yellow change and red clearance intervals?
What is the difference between priority control and preemption control, such as for emergency vehicles?
Does the MUTCD allow changing from a stop-and-go signal operation to a flashing mode during low volume periods?
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?
The 2009 MUTCD has lowered the recommended walking speed for calculating the Pedestrian Clearance Time from 4.0 ft/sec. to 3.5 ft/sec. But Section 4E.06 indicates that a walking speed of 3.0 ft/sec is also to be used. Where should 3.0 ft/sec be used instead of 3.5 ft/sec?
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?
Does the MUTCD allow the use of a "Leading Pedestrian Interval"?
The 2009 MUTCD now requires pedestrian countdown signals to be used except when the pedestrian change interval is 7 seconds or less. 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?
Table I-2 lists a December 22, 2013 compliance date for Section 4E.07 pedestrian countdown signal hardware requirements. Does that mean that pedestrian countdowns must be installed at all locations by that date?
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?
Is there any guidance on bicycle or equestrian signals, such as design and functional requirements?
Why does Section 4F.02 say that Pedestrian Hybrid Beacons should not be installed at or within 100 feet of side streets or driveways that are controlled by STOP or YIELD signs? Sometimes the only reasonable place to install a hybrid pedestrian beacon is at the intersection.
Why are Rectangular Rapid Flashing Beacons (RRFB) not in the 2009 MUTCD?
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)?
What is the appropriate color of In-Roadway Warning Lights used with crosswalks? Section 4N.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?

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 the U.S. has an estimated 2009 population of 307 million, we've got over 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 a 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: 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: 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. See Section 4C.01, paragraph 14, in the 2009 MUTCD.

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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: 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 factor 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: 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: 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/2009/part4/part4c.htm.

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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: Where did the numbers for the Pedestrian Volume and School Crossing signal warrants come from?

A: The Pedestrian Volume warrant (currently Warrant 4) has been in the MUTCD since the 1935 edition. In the 2009 edition, the warrant criteria and numbers for this warrant were revised based on research as documented in the 2006 report "Improving Pedestrian Safety at Unsignalized Pedestrian Crossings" (TCRP Report 112/NCHRP Report 562.). 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: Sections 4D.01 and 4D.32 of the 2009 MUTCD refer to "covering" of signal faces as one of the acceptable methods for indicating a signal is not in operation. In my jurisdiction, yellow retroreflective borders are used on the signal backplates of some signal faces. If such a face is to be covered, are there any specific requirements about covering the yellow retroreflective backplate borders?

A: One of the purposes of adding a yellow retroreflective border to the backplate (as allowed by Section 4D.12, paragraph 21) is to helps road users to recognize the presence of a signalized intersection during a power failure and react appropriately, such as treating the intersection as an all-way stop, as is required by law in some States. On the other hand, the purpose of covering a signal face that is out of service, such as before it is placed in service, or during seasonal shutdowns, is to avoid misleading unfamiliar road users into thinking that the intersection is signalized but the power has failed, because that could cause some road users to unexpectedly come to a stop, when no such stop is required by the right-of-way controls that are in place at the intersection. Therefore, it is inappropriate for the yellow retroreflective backplate border, if used, to be visible when the signal face is otherwise "covered". In February 2010, the FHWA issued Official Interpretation #4(09)-001(I) stating that that if the signal faces have backplates with yellow borders, the entire faces, including the backplates, should be covered. Additionally, if the signal faces are turned, rather than covered, they should be oriented such that the yellow backplate borders will not reflect light back to road users on any of the approaches to the intersection.

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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 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, paragraph 03, 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: Where the cross street is one-way, can a vertical green arrow indication be substituted for circular green, to emphasize that wrong-way turns are not allowed into that one-way cross street?

A: It depends. Section 4D.05, paragraph 03, item F.1 only allows the display of a green arrow (including the vertical green arrow as well as turn arrows) to a movement that is not in conflict with other movements that are moving on a green or yellow indication. A left turn from the opposing approach that is allowed to move at the same time on a permissive basis on a circular green or flashing yellow arrow would be in conflict with the thru movement, as defined in Section 4D.05, so that thru movement could not be shown a vertical green arrow. A vertical green arrow could be displayed if the opposing approach has no simultaneous left turn because the left turn is: 1) geometrically not possible, 2) prohibited, or 3) controlled by a "protected only" mode of operation.

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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: Section 4D.26 of the 2009 MUTCD specifically prohibits flashing green, vehicular countdown displays, or other similar displays intended to display a "pre-yellow." 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: Are strobe lights allowed in red signals?

A: No, they are not allowed. Section 4D.06 of the 2009 MUTCD specifically prohibits strobes within or adjacent to any signal indication. 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 or adjacent to traffic signals and no further experimentations with these types of strobe lights in traffic signals will be approved.

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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.06 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.06 also requires the design, illumination, and color all signal indications, including those using Led's, 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: Do the Institute of Transportation Engineers (ITE) Vehicle Traffic Control Signal Heads standards include the new U-turn arrow signal indications?

A: No, not yet, but the U-turn arrow details are anticipated to be developed by ITE and incorporated into an upcoming revision of their standard.

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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: 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, it 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: "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: Why does the 2009 MUTCD recommend against locating a signal face that displays a circular green indication above or in front of an exclusive left turn lane?

A: Section 4D.13, paragraph 09, contains this Guidance: "For new or reconstructed signal installations, on an approach with an exclusive turn lane(s) for a left-turn (or U-turn to the left) movement and with opposing vehicular traffic, signal faces that display a CIRCULAR GREEN signal indication should not be post-mounted on the far-side median or mounted overhead above the exclusive turn lane(s) or the extension of the lane(s)." This provision is based on research (reported in NCHRP Report 493) which found that the circular green permissive left-turn indication is confusing to some left-turn drivers who assume it provides right-of-way during the permissive interval. The placement of the circular green indication directly above or in line with an exclusive left-turn lane exacerbates the safety issues with this display. Research has found that displaying a circular green signal indication directly over an exclusive left-turn lane led to a higher left-turn crash rate than "shared" displays placed over the lane line between the left-turn lane and the adjacent through lane or to the right of that line. Placing the shared signal display over the lane line or to the right of it helps to promote the idea that the signal display with the circular green indication is being shared by the left turn and through lanes. This can help reduce the infrequent but very dangerous occurrence of the circular green permissive indication being misunderstood as a protected "go" indication by a left-turn driver.

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Q: My agency prefers to have a signal face over each lane on the approach, including left turn lanes that are operated as "permissive-protected" or "permissive only" mode left turns. Is there a way to do that without violating paragraph 09 of Section 4D.13?

A: Yes, but only if the signal face over the left-turn lane does not have a circular green in it and instead uses a flashing yellow arrow to indicate the permissive movement. The flashing yellow arrow is now available for optional use as the permissive turn display (see Sections 4D.17 through 4D.20 for details.)

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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 2009 MUTCD now require red arrows in protected-only mode left turn signals?

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. Therefore, the proposal to eliminate red arrows from the MUTCD was not adopted in the 2000 edition. Most States are now using red arrows. The updated Older Driver Handbook that is expected to be published in 2010 will be revised accordingly. The 2009 MUTCD now makes red left arrow the standard display for protected-only mode left-turn signal faces.

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Q: My State still 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. Until we replace the circular reds with red left arrows, 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: The 2009 MUTCD has eliminated the option of using a circular red in a "protected-only" mode left turn signal face. Over time, all such circular reds must be replaced with red left turn arrow indications. And, in the meantime, where circular reds are still in use in a left turn signal face, R3-5L or R10-5 signs cannot be used to identify it as a left turn signal. 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 (R10-10L) 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: Does the MUTCD now require agencies to provide a flashing yellow arrow indication for a left-turn movement for the permissive left-turn phase?

A: No, this is not mandatory, but the flashing yellow arrow is now allowed in the 2009 MUTCD as an optional alternative display for PPLT or "permissive only" left turn movements (see Sections 4D.17 through 4D.20). 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. An NCHRP follow-up study found that converting circular green permissive left-turn displays to flashing yellow arrow improved safety. Flashing yellow arrow displays are also now allowed for use with permissive right-turn movements (see Sections 4D.21 through 4D.24.)

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Q: What sign should be used to explain to drivers what flashing yellow arrow means?

A: The MUTCD does not include a standard sign for this purpose, because research has shown that no sign is needed. Researchers found that the flashing yellow arrow display is intuitively obvious in meaning to drivers and that an explanatory sign was unnecessary. See NCHRP Report 493.

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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: Section 4D.26 of the 2009 MUTCD requires the duration of the yellow change interval to be determined using engineering practices, and indicates that such engineering practices can be found in two books published by ITE. (Visit ITE's website at www.ite.org, where you will find additional information under "Technical Information".) 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, as noted in the ITE guidelines.

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Q: Are the ITE formulas the only "engineering practices" that can be used to determine duration of yellow change and red clearance intervals?

A: No, the MUTCD just lists the ITE publications as examples of engineering practices for these determinations. However, the FHWA suggests that the ITE guidelines be used as a starting point, because 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. Significant safety benefits have been found to result when yellow change intervals are retimed using the ITE guidelines.

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Q: What is the difference between priority control and preemption control, such as for emergency vehicles?

A: Section 4D.27 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 drawbridge signals) and trains (at signals at or near railroad crossings).

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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, this is specifically allowed by paragraph 07 in Section 4D.28 of the 2009 MUTCD, 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. Also, Section 4C.04 allows a signal warranted only by Warrant #3 (Peak Hour) to be operated in the flashing mode during the hours the volume criteria of warrant #3 are not met.

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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 2009 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: The 2009 MUTCD has lowered the recommended walking speed for calculating the Pedestrian Clearance Time from 4.0 ft/sec. to 3.5 ft/sec. But Section 4E.06 indicates that a walking speed of 3.0 ft/sec is also to be used. Where should 3.0 ft/sec be used instead of 3.5 ft/sec?

A: The 3.0 ft/sec walking speed is indicated for use in paragraph 14 of Section 4E.06. This is used as a "cross-check" calculation to determine if there is sufficient crossing time for slower pedestrians, such as those in wheelchairs or who are visually disabled, to cross wide streets. In this particular calculation, instead of using the curb-to-curb crossing distance, the distance used is measured from the pedestrian pushbutton (or, if none, from 6 feet back from the face of curb) to the far side curb. That distance in feet is divided by the 3.0 ft/sec assumed walking speed to obtain a value in number of seconds (for purposes of this example, let's call this value the "Slower Ped Time.") The Walk interval is allowed to be used to satisfy the calculated "Slower Ped Time," so the sum of the duration of the Walk interval (typically at least 7 sec.) plus the duration of the Pedestrian Clearance Time that was previously calculated using the regular 3.5 ft/sec walking speed is compared to the calculated "Slower Ped Time." For very wide streets, generally in the range of 95-100 feet or more, the calculations may find that the Slower Ped Time exceeds the calculated Pedestrian Clearance Time. In that case, the Walk interval, rather than the Pedestrian Clearance Time, should be increased in duration to satisfy the 3.0 ft/sec criterion.

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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 might 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 the 3.5 feet per second rate recommended by Section 4E.06, or slower if necessary.) Suppose that, based on the assumed walking speed and the width of road to be crossed, 20 seconds is calculated as the needed pedestrian clearance time. Section 4E.06 of the 2009 MUTCD allows the pedestrian clearance time to be either 1) contained totally within the vehicular green interval (in which case the 20 seconds is set on the controller as the pedestrian change interval flashing UPRAISED HAND time), OR 2) split between the green interval and some or all of the yellow interval. (However, there must always be a minimum of 3 seconds of "buffer interval" during which steady UPRAISED HAND must be displayed prior to release of any conflicting traffic.) Including the some or all of 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. If that is going to be considered for a given approach with a yellow change interval of 4 seconds, followed by a red clearance interval of 3 seconds or more to serve as the required "buffer," then that 4 seconds of yellow could 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 (flashing UPRAISED HAND) interval. Figure 4E-2 illustrates this concept.

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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: Again, it depends. See the discussion under FAQ number 33 above, and also refer to Figure 4E-2 in the 2009 MUTCD. That figure illustrates the relationships of pedestrian intervals and pedestrian displays to vehicular intervals and displays.

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Q: Does the MUTCD allow the use of a "Leading Pedestrian Interval"?

A: Yes, the leading pedestrian interval (LPI) is now specifically allowed by Section 4E.06 of the 2009 MUTCD. 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 at some locations where they determine it is needed, and its use is increasing. The Pedestrian User Guide published by FHWA and available on the Walkinginfo.org web site indicates that studies have found the 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.

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Q: The 2009 MUTCD now requires pedestrian countdown signals to be used except when the pedestrian change interval is 7 seconds or less. 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: Table I-2 lists a December 22, 2013 compliance date for Section 4E.07 pedestrian countdown signal hardware requirements. Does that mean that pedestrian countdowns must be installed at all locations by that date?

A: No. The December 22, 2013 date was established upon adoption of the 2003 edition of the MUTCD. The "hardware requirements" that must be complied with by that date are the provisions first established in the 2003 MUTCD (and still in effect) regarding the size, color, and location of the countdown numerals — IF countdowns are used. This 2013 date is the deadline for replacing any existing countdown hardware that doesn't meet those requirements. With the adoption of the 2009 MUTCD, any new countdowns installed from now onward must meet not only the hardware requirements but also the new provisions added in the 2009 edition, including the new requirement that any new or replacement pedestrian signals being installed must include countdowns unless the pedestrian change interval (flashing UPRAISED HAND) is 7 sec. or less. There is no specific date for adding countdowns to those pedestrian signals that do not currently have them. Such additions should be made as a part of the jurisdiction's plans for systematic upgrading of all their signals.

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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. Future research may lead to changes in how the pedestrian change interval is displayed, to eliminate potentially conflicting meanings.

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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 Public Right-of-Way Accessibility Guidelines (PROWAG). 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. The FHWA's policy is to consider the U.S. Access Board's draft PROWAG as recommended practice for new and reconstructed signals. 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: 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: Why does Section 4F.02 say that Pedestrian Hybrid Beacons should not be installed at or within 100 feet of side streets or driveways that are controlled by STOP or YIELD signs? Sometimes the only reasonable place to install a hybrid pedestrian beacon is at the intersection.

A: The FHWA has been discouraging "half-signals" for several decades because of the issues such designs cause when the interruption of the major street traffic flow by a pedestrian actuation is used by side street drivers as their opportunity to turn onto the major street, in conflict with the crossing pedestrians. Hybrid beacons placed at or adjacent to an intersection with a stop or yield sign controlled side street is a half-signal with the same operational and safety issues. The provision in Section 4F.02 is also consistent with the anti-half-signal provisions that were adopted in Sections 4C.05 and 4C.06. Please note that these provisions in 4C.05, 4C.06, and 4F.02 are Guidance, not Standards. Thus, based on an engineering study or engineering judgment, a jurisdiction can decide to install the device at such an intersection if it determines that is the best location for it, considering all pertinent factors, and/or there are mitigating measures, such as blank-out No Right Turn/No Left Turn signs for the side street or making the side street one-way away from the intersection. The decisions should be documented in the jurisdictions' files as basis for deviating from a Guidance statement in the MUTCD. It should also be noted that the National Committee on Uniform Traffic Control Devices (NCUTCD) has recommended to FHWA that the Section 4F.02 guidance against installing pedestrian hybrid beacons within 100 feet of an intersection should be removed from the MUTCD, because a study of hybrid beacons at intersections in Tucson, Arizona, did not find significant operational or safety issues. The FHWA will give consideration to proposing the removal of the 100 feet guidance for the next edition of the MUTCD.

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Q: Why are Rectangular Rapid Flashing Beacons (RRFB) not in the 2009 MUTCD?

A: The Rectangular Rapid Flash Beacon (RRFB) is not in the 2009 MUTCD because it was granted Interim Approval status too late to include in the January 2008 Notice of Proposed Amendments (NPA). RRFB will have to go through the formal rulemaking process via a future NPA, public review and comment, and then a final rule for a future MUTCD. However, until that occurs, the RRFB can continue to be used under the provisions of Interim Approval #IA-11 dated July 16, 2008. No "testing" or data collection is required for such use.

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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 4N.01 and 4N.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 4N 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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Q: What is the appropriate color of In-Roadway Warning Lights used with crosswalks? Section 4N.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 4N.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 at 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 4N.02 states that IRWLs "shall not be used at crosswalks controlled by YIELD signs, STOP signs, or traffic control signals" and Section 4N.01 states that IRWLs "shall not be used for any application that is not described in this Chapter." 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 4N.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 4N.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 4N.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 4N.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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