View source for 902.7 Flashing Operation of Traffic Control Signals (MUTCD Chapter 4G)

[[Category:902 Signals (MUTCD Part 4)|902.07]]
=={{SpanID|902.7.1}}902.7.1 Flashing Operation of Traffic Control Signals – General (MUTCD Section 4G.01)==

'''Standard. '''The light source of a flashing signal indication shall be flashed continuously at a rate of not less than 50 or more than 60 times per minute.

The displayed period of each flash shall be a minimum of ½ and a maximum of ⅔ of the total flash cycle.

Flashing signal indications shall comply with the requirements of other Sections of this Manual regarding visibility limiting or positioning of conflicting signal indications, except that flashing yellow signal indications for through traffic shall not be required to be visibility limited or positioned to minimize visual conflict for road users in separately-controlled turn lanes.

Each traffic control signal shall be provided with an independent flasher mechanism that operates in compliance with this Article.

A manual switch shall be provided to initiate the flashing mode. A conflict monitor (malfunction management unit) circuit and, if appropriate, an automatic means shall also be provided to initiate the flashing mode.

The flashing operation shall not be terminated by removing or turning off the controller unit or the conflict monitor (malfunction management unit) or both.

'''Support. '''There are two types of flashing operation: 
:A. All-direction cabinet flash – This type of flashing operation is initiated by the cabinet.  The cabinet can be put to flash via a manual switch, or if the signalized intersection is operating inappropriately via a conflict monitor (malfunction monitoring unit). 
:B. All-direction programmed flash – This type of flash operation is programmed into the controller to flash the signal during specific times every day.

'''Standard. '''All-direction cabinet flash is permitted to be made at any time. 

Actuated intersections shall run steady (stop-and-go) mode at all times and shall not utilize all-direction programmed flash, except for school signals as covered in [[902.11 Accessible Pedestrian Signals and Detectors (MUTCD Chapter 4K) #902.11.3|EPG 902.11.3]]. For pretimed intersections, every effort shall be made to upgrade the signalized intersection from pretimed to actuated operation. 

'''Guidance. '''Several factors should be used with good engineering judgment when making the decision to implement all-direction programmed flashing operation for pretimed intersections. Among these is crash history, presence of pedestrian signal indications, and sight distance. If correctable crashes were a significant factor in the justification for installation of the signal, then all-direction flashing operation should not be acceptable at any time.

'''Standard. '''If stopping sight distance is below the values listed in [[903.3 Warning Signs and Object Markers (MUTCD Chapter 2C) #tab903.3.1|Table 903.3.1]], then flashing operation shall not be considered.

'''Guidance. '''Fully actuated signals within a coordinated system should be analyzed for possible free operation when other signals within the system are operating in all-direction programmed flash. 

'''Support. '''An in-house MoDOT safety study identified that crashes at locations with late night/early morning flash tend to occur before 2 a.m. and in FHWA’s publication Signalized Intersections: Informational Guide (FHWA-HRT-04-091), it was found that an estimated 78% reduction in right-angle collisions and an estimated 32% reduction in all collisions can be expected with the removal from late night/early morning flash mode.

[[902.9 Pedestrian Control Features (MUTCD Chapter 4I) #902.9.6|EPG 902.9.6]] and [[902.11 Accessible Pedestrian Signals and Detectors (MUTCD Chapter 4K) #902.11.4|902.11.4]] contain information regarding the operation of pedestrian signal heads and accessible pedestrian signal detector push button locator tones, respectively, during flashing operation.

=={{SpanID|902.7.2}}902.7.2 Flashing Operation – Transition Into Flashing Mode (MUTCD Section 4G.02)==

'''Option. '''The transition from steady (stop-and-go) mode to flashing mode, if initiated by a conflict monitor (malfunction management unit) or by a manual switch, may be made at any time it is in fail-safe operation.

'''Standard. '''Programmed changes from steady (stop-and-go) mode to flashing mode shall be made under either of the following circumstances:
::A. At the end of the common major-street red interval (such as just prior to the start of the green in both directions on the major street), or
::B. Directly from a CIRCULAR GREEN signal indication to a flashing CIRCULAR YELLOW signal indication, or from a GREEN ARROW signal indication to a flashing YELLOW ARROW signal indication, or from a flashing YELLOW ARROW signal indication (see [[902.6 Steady (Stop-and-Go) Operation of Traffic Control Signals (MUTCD Chapter 4F) #902.6.2|EPG 902.6.2]], [[902.6 Steady (Stop-and-Go) Operation of Traffic Control Signals (MUTCD Chapter 4F) #902.6.4| 902.6.4]], [[902.6 Steady (Stop-and-Go) Operation of Traffic Control Signals (MUTCD Chapter 4F) #902.6.8|902.6.8]], [[902.6 Steady (Stop-and-Go) Operation of Traffic Control Signals (MUTCD Chapter 4F) #902.6.9|902.6.9]], [[902.6 Steady (Stop-and-Go) Operation of Traffic Control Signals (MUTCD Chapter 4F) #902.6.11|902.6.11]], and [[902.6 Steady (Stop-and-Go) Operation of Traffic Control Signals (MUTCD Chapter 4F) #902.6.15|902.6.15]]) to a flashing YELLOW ARROW signal indication in a different signal section.

During programmed changes into flashing mode, no green signal indication or flashing yellow signal indication shall be terminated and immediately followed by a steady red or flashing red signal indication without first displaying the steady yellow signal indication.

=={{SpanID|902.7.3}}902.7.3 Flashing Operation – Signal Indications During Flashing Mode (MUTCD Section 4G.03)==

'''Guidance. '''When a traffic control signal is operated in the flashing mode, there are two possible types of operation:
::A. Yellow-red flashing mode: For intersections where traffic volumes during flashing operation on the major street are significantly greater than traffic volumes on the minor street, a flashing yellow signal indication should be used for the major street and a flashing red signal indication should be used for the other approaches.
::B. Red-red flashing mode: For intersections where traffic volumes during flashing operation on all approaches are approximately equal, a flashing red signal indication should be used for all approaches. Complex intersections (5-leg, large widths, multiple dual left turn approaches) also operate with red indications for all approaches during flashing operation, regardless of traffic volumes.

When a system of interconnected signals is flashed, care should be taken to be consistent in flash color for the major street so as not to violate driver expectancy.

'''Support. '''A red/red flashing signal in the middle of a system of yellow/red flashing signals could lead to violations of the flashing red along the major street due to the expectancy of yellow flashing indications.

Fail-safe operation for a malfunctioning signal leads to all-direction flashing operation when tripped by a conflict monitor. Cabinet wiring determines all-direction flashing operation when a malfunction has occurred; this generally means malfunction flash will be red-red mode since it is wired the same as the start up from dark flash (see [[902.23 Traffic Signal Phasing and Operation #902.23.9|EPG 902.23.9]]).

'''Standard. '''When a traffic control signal is operated in the flashing mode, all of the green signal indications at the signalized location shall be dark (non-illuminated) and shall not be displayed in either a steady or flashing manner, except for single-section GREEN ARROW signal indications as provided in the fourth standard paragraph of this Article.

Flashing yellow signal indications shall be used on more than one approach to a signalized location only if those approaches do not conflict with each other.

When a traffic control signal is operated in the flashing mode, one and only one signal indication in every signal face at the signalized location shall be flashed.

No steady indications, other than a single-section signal face consisting of a continuously-displayed GREEN ARROW signal indication that is used alone to indicate a continuous movement in the steady (stop-and-go) mode, shall be displayed at the signalized location during the flashing mode. A single-section GREEN ARROW signal indication shall remain continuously displayed when the traffic control signal is operated in the flashing mode.

If a signal face includes both circular and arrow signal indications of the color that is to be flashed, only the circular signal indication shall be flashed. 

All signal faces that are flashed on an approach shall flash the same color, either yellow or red, except that separate turn signal faces (see [[902.6 Steady (Stop-and-Go) Operation of Traffic Control Signals (MUTCD Chapter 4F) #902.6.4|EPG 902.6.4]], [[902.6 Steady (Stop-and-Go) Operation of Traffic Control Signals (MUTCD Chapter 4F) #902.6.6|902.6.6]], [[902.6 Steady (Stop-and-Go) Operation of Traffic Control Signals (MUTCD Chapter 4F) #902.6.8|902.6.8]], [[902.6 Steady (Stop-and-Go) Operation of Traffic Control Signals (MUTCD Chapter 4F) #902.6.11|902.6.11]], [[902.6 Steady (Stop-and-Go) Operation of Traffic Control Signals (MUTCD Chapter 4F) #902.6.13|902.6.13]], and [[902.6 Steady (Stop-and-Go) Operation of Traffic Control Signals (MUTCD Chapter 4F) #902.6.15|902.6.15]]) shall be permitted to flash a RED ARROW signal indication when the adjacent through movement signal indications are flashed yellow. Shared signal faces (see [[902.6 Steady (Stop-and-Go) Operation of Traffic Control Signals (MUTCD Chapter 4F) #902.6.3|EPG 902.6.3]], [[902.6 Steady (Stop-and-Go) Operation of Traffic Control Signals (MUTCD Chapter 4F) #902.6.5|902.6.5]], [[902.6 Steady (Stop-and-Go) Operation of Traffic Control Signals (MUTCD Chapter 4F) #902.6.7|902.6.7]], [[902.6 Steady (Stop-and-Go) Operation of Traffic Control Signals (MUTCD Chapter 4F) #902.6.10|902.6.10]], [[902.6 Steady (Stop-and-Go) Operation of Traffic Control Signals (MUTCD Chapter 4F) #902.6.12|902.6.12]], and [[902.6 Steady (Stop-and-Go) Operation of Traffic Control Signals (MUTCD Chapter 4F) #902.6.14|902.6.14]]) for turn movements shall not be permitted to flash a CIRCULAR RED signal indication when the adjacent through movement signal indications are flashed yellow.

The appropriate RED ARROW or YELLOW ARROW signal indication shall be flashed when a signal face consists entirely of arrow indications. A signal face that consists entirely of arrow indications and that provides a protected only turn movement during the steady (stop-and-go) mode or that provides a flashing YELLOW ARROW signal indication for a permissive turn movement during the steady (stop-and-go) mode shall be permitted to flash the YELLOW ARROW signal indication during the flashing mode if the adjacent through movement signal indications are flashed yellow and if it is intended that a permissive turn movement not requiring a full stop by each turning vehicle be provided during the flashing mode.

'''Guidance. '''For dual or protected-only left turns programmed to flash, the indications should flash yellow arrow when the phasing was determined based on high traffic volumes. When the phasing was determined for intersection safety, the indications for the left turn should flash red.

Whether the signal flashes by cabinet wiring or controller programming, all signal indications should not flash simultaneously.

'''Support. '''Flashing all signal indications simultaneously causes a severe load fluctuation that reduces the life of the electrical equipment and can lead to malfunctions when the signal is in operation.

=={{SpanID|902.7.4}}902.7.4 Flashing Operation – Transition Out of Flashing Mode (MUTCD Section 4G.04)==

'''Standard. '''All changes from flashing mode to steady (stop-and-go) mode shall be made under one of the following procedures:
::A. Yellow-red flashing mode: Changes from flashing mode to steady (stop-and-go) mode shall be made at the beginning of the major-street green interval (when a green signal indication is displayed to through traffic in both directions on the major street), or if there is no common major-street green interval, at the beginning of the green interval for the major traffic movement on the major street.
::B. Red-red flashing mode: Changes from flashing mode to steady (stop-and-go) mode shall be made by changing the flashing red indications to steady red indications followed by appropriate green indications to begin the steady mode cycle. These green indications shall be the beginning of the major-street green interval (when a green signal indication is displayed to through traffic in both directions on the major street) or if there is no common major-street green interval, at the beginning of the green interval for the major traffic movement on the major street.

The steady red clearance interval provided during the change from red-red flashing mode to steady (stop-and-go) mode shall have a minimum duration of 6 seconds.

When changing from the yellow-red flashing mode to steady (stop-and-go) mode at a location where there is a common major-street green interval, the flashing red signal indications for the minor street shall immediately change to steady red signal indications, and the flashing yellow signal indications for the through movements on the major street shall change to green signal indications in both directions (after the minor-street signal indications have been steady red for a short time, if desired), or the flashing yellow signal indications for the through movements on the major street shall change to steady yellow signal indications followed by a steady red clearance interval before changing to green signal indications in both directions.

'''Guidance. '''When changing from the yellow-red flashing mode to steady (stop-and-go) mode at a location where there is no common major-street green interval, the flashing red signal indications for the minor street should immediately change to steady red signal indications, and the flashing yellow signal indications for the through movements on the major street should change to steady yellow signal indications followed by a steady red clearance interval before changing to green signal indications for the major traffic movement on the major street.

'''Standard. '''During programmed changes out of flashing mode, no flashing yellow signal indication shall be terminated and immediately followed by a steady red or flashing red signal indication without first displaying a steady yellow signal indication.