902.1 General (MUTCD Chapter 4A)

902.1.1 Types (MUTCD Section 4A.01)

Support. The following types and uses of highway traffic signals and devices are discussed in EPG 902: traffic control signals; bicycle signal faces; pedestrian signal heads; hybrid beacons; rectangular rapid flashing beacons; emergency-vehicle traffic control signals; traffic control signals for one-lane, two-way facilities; traffic control signals for freeway entrance ramps; flashing beacons; and in-roadway warning lights.

902.1.2 Meanings of Signal Indications (MUTCD Section 4A.02)

Support. The “Uniform Vehicle Code” (see EPG 911 (MUTCD Section 1A.06)) is the primary source for the standards for the meanings of vehicular signal indications to both vehicle operators and pedestrians as provided in EPG 902.1.3 and 902.1.4, the standards for the meanings of separate bicycle signal face indications as provided in EPG 902.1.5, and the standards for the meanings of separate pedestrian signal head indications as provided in EPG 902.1.6.

The physical area that is defined as being “within the intersection” is dependent upon the conditions that are described in the definition of an intersection in EPG 911 (MUTCD Section 1C.02).

902.1.3 Meanings of Steady Vehicular Signal Indications (MUTCD Section 4A.03)

Standard. The following meanings shall be given to steady highway traffic signal indications for vehicles and pedestrians:

A. Steady green signal indications shall have the following meanings:

1. Vehicular traffic facing a CIRCULAR GREEN signal indication is permitted to proceed straight through or turn right or left or make a U-turn movement except as such movement is modified by lane-use signs, turn prohibition signs, lane markings, roadway design, separate turn signal indications, or other traffic control devices. Vehicular traffic facing a CIRCULAR GREEN signal indication shall only be permitted to make a U-turn movement from the left-turn lane where Intersection Lane Control signs are installed indicating that the movement is permitted (see EPG 903.2.25). The Highway Safety and Traffic Division shall approve all new or reconstructed signal installations where U-turns are permitted during a permissive phase. Such vehicular traffic, including vehicles turning right or left or making a U-turn movement, shall yield the right-of-way to:

   (a) Pedestrians lawfully within an associated crosswalk, and

   (b) Other vehicles lawfully within the intersection.

   In addition, vehicular traffic turning left or making a U-turn movement to the left shall yield the right-of-way to other vehicles approaching from the opposite direction so closely as to constitute an immediate hazard during the time when such turning vehicle is moving across or within the intersection.
2. Vehicular traffic facing a GREEN ARROW signal indication, displayed alone or in combination with another signal indication, is permitted to cautiously enter the intersection only to make the movement indicated by such arrow, or such other movement as is permitted by other signal indications displayed at the same time. Vehicular traffic facing a GREEN ARROW signal indication shall only be permitted to make a U-turn movement from the left-turn lane where Intersection Lane Control signs are installed indicating that the movement is permitted (see EPG 903.2.25). Such vehicular traffic, including vehicles turning right or left or making a U-turn movement, shall yield the right-of-way to:

   (a) Pedestrians lawfully within an associated crosswalk, and

   (b) Other vehicles lawfully within the intersection.

3. Pedestrians facing a CIRCULAR GREEN signal indication, unless otherwise directed by a pedestrian signal indication or other traffic control device, are permitted to proceed across the roadway within any marked or unmarked associated crosswalk. The pedestrian shall yield the right-of-way to vehicles lawfully within the intersection or so close as to create an immediate hazard at the time that the green signal indication is first displayed.
4. Pedestrians facing a GREEN ARROW signal indication, unless otherwise directed by a pedestrian signal indication or other traffic control device, shall not cross the roadway.

B. Steady yellow signal indications shall have the following meanings:

1. Vehicular traffic facing a steady CIRCULAR YELLOW signal indication is thereby warned that the related green movement or the related flashing arrow movement is being terminated or that a steady red signal indication will be displayed immediately thereafter when vehicular traffic shall not enter the intersection. The rules set forth concerning vehicular operation under the movement(s) being terminated shall continue to apply while the steady CIRCULAR YELLOW signal indication is displayed.
2. Vehicular traffic facing a steady YELLOW ARROW signal indication is thereby warned that the related GREEN ARROW movement or the related flashing arrow movement is being terminated. The rules set forth concerning vehicular operation under the movement(s) being terminated shall continue to apply while the steady YELLOW ARROW signal indication is displayed.
3. Pedestrians facing a steady CIRCULAR YELLOW or YELLOW ARROW signal indication, unless otherwise directed by a pedestrian signal indication or other traffic control device shall not start to cross the roadway.

C. Steady red signal indications shall have the following meanings:

1. Vehicular traffic facing a steady CIRCULAR RED signal indication, unless entering the intersection to make another movement permitted by another signal indication, shall stop at a clearly marked stop line; but if there is no stop line, traffic shall stop before entering the crosswalk on the near side of the intersection; or if there is no crosswalk, then before entering the intersection; and shall remain stopped until a signal indication to proceed is displayed, or as provided below. Except when a traffic control device is in place prohibiting a turn on red or a steady RED ARROW signal indication is displayed, vehicular traffic facing a steady CIRCULAR RED signal indication is permitted to enter the intersection to turn right after stopping. The right to proceed with the turn shall be subject to the rules applicable after making a stop at a STOP sign.
2. Vehicular traffic facing a steady RED ARROW signal indication shall not enter the intersection to make the movement indicated by the arrow and, unless entering the intersection to make another movement permitted by another signal indication, shall stop at a clearly marked stop line; but if there is no stop line, before entering the crosswalk on the near side of the intersection; or if there is no crosswalk, then before entering the intersection; and shall remain stopped until a signal indication or other traffic control device permitting the movement indicated by such RED ARROW is displayed. When a traffic control device is in place permitting a turn on a steady RED ARROW signal indication, vehicular traffic facing a steady RED ARROW signal indication is permitted to enter the intersection to make the movement indicated by the arrow signal indication, after stopping. The right to proceed with the turn shall be limited to the direction indicated by the arrow and shall be subject to the rules applicable after making a stop at a STOP sign.
3. Unless otherwise directed by a pedestrian signal indication or other traffic control device, pedestrians facing a steady CIRCULAR RED or steady RED ARROW signal indication shall not enter the roadway.

902.1.4 Meanings of Flashing Vehicular Signal Indications (MUTCD Section 4A.04)

Standard. The following meanings shall be given to flashing highway traffic signal indications for vehicles and pedestrians:

A. A flashing green signal indication has no meaning and shall not be used.

B. Flashing yellow signal indications shall have the following meanings:

1. Vehicular traffic, on an approach to an intersection, facing a flashing CIRCULAR YELLOW signal indication is permitted to cautiously enter the intersection to proceed straight through or turn right or left or make a U-turn except as such movement is modified by lane use signs, turn prohibition signs, lane markings, roadway design, separate turn signal indications, or other traffic control devices. Vehicular traffic facing a flashing CIRCULAR YELLOW signal indication shall only be permitted to make a U-turn movement from the left-turn lane where Intersection Lane Control signs are installed indicating that the movement is permitted (see EPG 903.2.25). The Highway Safety and Traffic Division shall approve all new or reconstructed signal installations where U-turns are permitted during a permissive phase. Such vehicular traffic, including vehicles turning right or left or making a U-turn, shall yield the right-of-way to:

   (a) Pedestrians lawfully within an associated crosswalk, and

   (b) Other vehicles lawfully within the intersection.

   In addition, vehicular traffic turning left or making a U-turn to the left shall yield the right-of-way to other vehicles approaching from the opposite direction so closely as to constitute an immediate hazard during the time when such turning vehicle is moving across or within the intersection.
2. Vehicular traffic, on an approach to an intersection, facing a flashing YELLOW ARROW signal indication, displayed alone or in combination with another signal indication, is permitted to cautiously enter the intersection only to make the movement indicated by such arrow, or other such movement as is permitted by other signal indications displayed at the same time. Vehicular traffic facing a flashing YELLOW ARROW signal indication shall only be permitted to make a U-turn movement from the left-turn lane where Intersection Lane Control signs are installed indicating that the movement is permitted (see EPG 903.2.25). The Highway Safety and Traffic Division shall approve all new or reconstructed signal installations where U-turns are permitted during a permissive phase. Such vehicular traffic, including vehicles turning right or left or making a U-turn, shall yield the right-of-way to:

   (a) Pedestrians lawfully within an associated crosswalk, and

   (b) Other vehicles lawfully within the intersection.

   In addition, vehicular traffic turning left or making a U-turn to the left shall yield the right-of-way to other vehicles approaching from the opposite direction so closely as to constitute an immediate hazard during the time when such turning vehicle is moving across or within the intersection.
3. Pedestrians facing any flashing yellow signal indication at an intersection, unless otherwise directed by a pedestrian signal indication or other traffic control device, are permitted to proceed across the roadway within any marked or unmarked associated crosswalk. Pedestrians shall yield the right-of-way to vehicles lawfully within the intersection at the time that the flashing yellow signal indication is first displayed.
4. When a flashing CIRCULAR YELLOW signal indication(s) is displayed as a beacon (see EPG 902.18) to supplement another traffic control device, road users are notified that there is a need to pay extra attention to the message contained thereon or that the regulatory or warning requirements of the other traffic control device, which might not be applicable at all times, are currently applicable.

C. Flashing red signal indications shall have the following meanings:

1. Vehicular traffic, on an approach to an intersection, facing a flashing CIRCULAR RED signal indication shall stop at a clearly marked stop line; but if there is no stop line, before entering the crosswalk on the near side of the intersection; or if there is no crosswalk, at the point nearest the intersecting roadway where the driver has a view of approaching traffic on the intersecting roadway before entering the intersection. The right to proceed shall be subject to the rules applicable after making a stop at a STOP sign.
3. Pedestrians facing any flashing red signal indication at an intersection, unless otherwise directed by a pedestrian signal indication or other traffic control device, are permitted to proceed across the roadway within any marked or unmarked associated crosswalk. Pedestrians shall yield the right-of-way to vehicles lawfully within the intersection at the time that the flashing red signal indication is first displayed.
4. When a flashing CIRCULAR RED signal indication(s) is displayed as a beacon (see EPG 902.18) to supplement another traffic control device, road users are notified that there is a need to pay extra attention to the message contained thereon or that the regulatory requirements of the other traffic control device, which might not be applicable at all times, are currently applicable. Use of this signal indication shall be limited to supplementing STOP (R1-1), DO NOT ENTER (R5-1), or WRONG WAY (R5-1a) signs, and to applications where compliance with the supplemented traffic control device requires a stop at a designated point.

902.1.5 Meanings of Bicycle Symbol Signal Indications (MUTCD Section 4A.05)

Guidance. Bicycle symbol signal indications are not currently used on MoDOT facilities. Contact the Highway Safety and Traffic Division for guidance.

Standard. The following meanings shall be given to bicycle symbol signal indications for bicyclists:

A. Bicyclists facing a steady GREEN BICYCLE signal indication are permitted to enter the intersection only to make the movement indicated by the lane-use arrow(s) displayed on the Bicycle Signal sign (see Section 9B.22) that is located immediately adjacent to the signal face. Bicyclists proceeding into the intersection during the display of the steady GREEN BICYCLE signal indication shall yield the right-of-way to:

1. Pedestrians lawfully within an associated crosswalk, and
2. Other vehicles lawfully within the intersection.

B. Bicyclists facing a steady YELLOW BICYCLE signal indication are thereby warned that the related green movement is being terminated and that a steady RED BICYCLE signal indication will be displayed immediately thereafter when bicyclists shall not enter the intersection. The rules set forth concerning bicycle operation under the movement being terminated shall continue to apply while the steady YELLOW BICYCLE signal indication is displayed.

C. Bicyclists facing a steady RED BICYCLE signal indication shall not enter the intersection to make the movement indicated by the lane-use arrow(s) displayed on the Bicycle Signal sign (see Section 9B.22) that is located immediately adjacent to the signal face and, unless entering the intersection to make another movement permitted by another bicycle symbol signal indication, shall stop at a clearly marked stop line; but if there is no stop line, before entering the crosswalk on the near side of the intersection; or if there is no crosswalk, then before entering the intersection; and shall remain stopped until a GREEN BICYCLE signal indication permitting the movement indicated by such RED BICYCLE signal indication is displayed.

Except when a traffic control device is in place prohibiting a turn on red, bicyclists facing a steady RED BICYCLE signal indication are permitted to enter the intersection to turn right if there are no approach lanes for motor vehicle traffic to their right. The right to proceed with the turn shall be subject to the rules applicable after making a stop at a STOP sign.

D. A flashing GREEN BICYCLE signal indication has no meaning and shall not be used.

E. A flashing YELLOW BICYCLE signal indication has no meaning and shall not be used.

F. Bicyclists facing a flashing RED BICYCLE signal indication shall stop at a clearly marked stop line; but if there is no stop line, before entering the crosswalk on the near side of the intersection; or if there is no crosswalk, at the point nearest the intersecting roadway where the bicyclist has a view of approaching traffic on the intersecting roadway before entering the intersection. The right to proceed in the direction indicated by the lane-use arrow(s) displayed on the Bicycle Signal sign (see Section 9B.22) that is located immediately adjacent to the signal face shall be subject to the rules applicable after making a stop at a STOP sign.

902.1.6 Meanings of Pedestrian Signal Indications (MUTCD Section 4A.06)

Standard. Pedestrian signal indications shall have the following meanings:

A. A flashing WALKING PERSON (symbolizing WALK) signal indication has no meaning and shall not be used.

B. Pedestrians facing a steady WALKING PERSON (symbolizing WALK) signal indication shall be permitted to start to cross the roadway in the direction of the signal indication, possibly in conflict with turning vehicles. Pedestrians shall yield the right-of-way to vehicles lawfully within the intersection at the time that the WALKING PERSON (symbolizing WALK) signal indication is first shown.

C. Pedestrians facing a flashing UPRAISED HAND (symbolizing DONT WALK) signal indication shall not start to cross the roadway in the direction of the signal indication. Any pedestrian who has already started to cross the roadway on a steady WALKING PERSON (symbolizing WALK) signal indication shall continue to proceed to the far side of the traveled way of the street or highway, unless otherwise directed by a traffic control device to proceed only to the median of a divided highway or only to some other island or pedestrian refuge area (see EPG 620.3.10).

D. Pedestrians facing a steady UPRAISED HAND (symbolizing DONT WALK) signal indication shall not enter the roadway in the direction of the signal indication.

902.1.7 Lateral Offset of Signal Supports and Cabinets (MUTCD Section 4A.07)

Guidance. The following items should be considered when placing signal supports and cabinets:

A. Reference should be made to the “Roadside Design Guide,” 4th Edition, 2011, AASHTO, and to the U.S. Department of Justice 2010 ADA Standards for Accessible Design, September 15, 2010, 28 CFR 35 and 36, Americans with Disabilities Act of 1990.

B. Signal supports should be placed as far as practicable from the edge of the traveled way without adversely affecting the visibility of the signal indications.

C. Where supports cannot be located based on the recommended AASHTO clearances, consideration should be given to the use of appropriate safety devices.

D. No part of a concrete foundation for a breakaway signal support should extend more than 4 inches above the ground level at any point. This limitation does not apply to the concrete foundation for a rigid support.

E. In order to minimize hindrance to the passage of persons with physical disabilities, a signal support or controller cabinet should not obstruct the sidewalk or the pedestrian access route such that less than 4 feet of clear space is available, or access from the sidewalk to the crosswalk. Refer to the Public Right-of-Way Accessibility Guidelines, published by the U.S. Access Board for pedestrian access route.

F. Controller cabinets should be located as far as practicable from the edge of the roadway.

G. On medians, the minimum clearances provided in Items A through E for signal supports should be obtained, if practicable.

902.1.8 Use of Signs at Signalized Locations (MUTCD Section 4A.08)

Support. Traffic signal signs are sometimes used at highway traffic signal locations to instruct or guide pedestrians, bicyclists, or motorists. Among the signs typically used at or on the approaches to signalized locations are movement prohibition signs (see EPG 903.2.24), lane-control signs (see EPG 903.2.25 through EPG 903.2.27), pedestrian crossing signs (see EPG 903.2.46), pedestrian and bicycle actuation signs (see EPG 903.2.47), traffic signal signs (see EPG 903.2.48 and 2C.44), No Turn on Red signs (see EPG 903.2.49), Signal Ahead warning signs (see Section 2C.35), Street Name signs (see Section 2D.45), and Advance Street Name signs (see Section 2D.46).

Guidance. Regulatory, warning, and guide signs should be used at highway traffic signal locations as provided in Part 2 and as specifically provided elsewhere in EPG 902.

Support. EPG 903.2.25 contains information regarding the use of overhead lane-control signs on signalized approaches where lane drops, multiple-lane turns involving combined through-and-turn lanes, or other lane-use regulations that would be unexpected by unfamiliar road users are present.

Standard. If used, illuminated traffic signal signs shall be designed and mounted in such a manner as to avoid glare and reflections that seriously detract from the signal indications. Highway traffic signal faces shall be given dominant position and brightness to maximize their priority in the overall display.

The minimum vertical clearance and horizontal offset of the total assembly of traffic signal signs (see EPG 903.2.48) shall comply with the provisions of EPG 902.4.9 and 902.4.10.

STOP signs shall not be used in conjunction with any highway traffic signal operation, except in either of the following cases:

A. If the signal indication for an approach is a flashing red at all times, or

B. If a minor street or driveway is located within or adjacent to an area controlled by a traffic control signal, but does not require separate traffic signal control because an extremely low potential for conflict exists.

902.1.9 Use of Pavement Markings at Signalized Locations (MUTCD Section 4A.09)

Support. Pavement markings that clearly communicate the operational plan of an intersection to road users play an important role in the effective operation of highway traffic signals. By designating the number of lanes, the use of each lane, the length of additional lanes on the approach to an intersection, crosswalks, and the proper stopping points, the engineer can design the signal phasing and timing to best match the goals of the operational plan.

Guidance. Pavement markings should be used at highway traffic signal locations as provided in EPG 620. If the road surface will not retain pavement markings, signs should be installed to provide the needed road user information.

902.1.10 Responsibility for Operation and Maintenance (MUTCD Section 4A.10)

Guidance. Prior to installing any highway traffic signal, the responsibility for the maintenance of the signal and all of the appurtenances, hardware, software, and the timing plan(s) should be clearly established by the responsible agency.

To this end the agency should:

A. Keep every controller assembly in effective operation in accordance with its predetermined timing schedule, check the operation of the controller assembly frequently enough to verify that it is operating in accordance with the predetermined timing schedule, and establish a policy to maintain a record of all timing changes and that only authorized persons are permitted to make timing changes;

B. Clean the optical system of the signal sections and replace the light sources as frequently as experience proves necessary;

C. Clean and service equipment and other appurtenances as frequently as experience proves necessary;

D. Provide for alternate operation of the traffic control signal during a period of failure, using flashing mode or manual control, or manual traffic direction by proper authorities as might be required by traffic volumes or congestion, or by erecting other traffic control devices;

E. Have properly-skilled maintenance personnel available without undue delay for all signal malfunctions and signal indication failures;

F. Maintain an inventory of spare equipment to minimize the interruption of highway traffic signal operation as a result of equipment failure;

G. Provide for the availability of properly-skilled maintenance personnel for the repair of all components;

H. Maintain the appearance of the signal displays and equipment; and

I. Follow appropriate procedures for operation and maintenance for all traffic signal control systems and equipment.

902.1.11 Signal Indications for Left-Turn Movements – General (MUTCD Section 4D.17)

Support. Left-turning traffic is controlled by one of four modes as follows:

A. Permissive Only Mode—turns made on a CIRCULAR GREEN signal indication or a flashing left-turn YELLOW ARROW signal indication after yielding to pedestrians, if any, and/or opposing traffic, if any.

B. Protected Only Mode—turns made only when a left-turn GREEN ARROW signal indication is displayed.

C. Protected/Permissive Mode—both modes can occur on an approach during the same cycle.

D. Variable Left-Turn Mode—the operating mode changes among the protected only mode and/or the protected/permissive mode and/or the permissive only mode during different periods of the day or as traffic conditions change.

Standard. U-turns to the left shall only be permitted at protected only mode left turns.

Option. In areas having a high percentage of older drivers, special consideration may be given to the use of protected only mode left-turn phasing, when appropriate.

Standard. During a permissive left-turn movement, the signal faces for through traffic on the opposing approach shall simultaneously display green or steady yellow signal indications. If pedestrians crossing the lane or lanes used by the permissive left-turn movement to depart the intersection are controlled by pedestrian signal heads, the signal indications displayed by those pedestrian signal heads shall not be limited to any particular display during the permissive left-turn movement.

During a protected left-turn movement, the signal faces for through traffic on the opposing approach shall simultaneously display steady CIRCULAR RED signal indications. If pedestrians crossing the lane or lanes used by the protected left-turn movement to depart the intersection are controlled by pedestrian signal heads, the pedestrian signal heads shall display a steady UPRAISED HAND (symbolizing DONT WALK) signal indication during the protected left-turn movement.

A protected only mode left-turn movement that does not begin and terminate at the same time as the adjacent through movement shall not be provided on an approach unless an exclusive left-turn lane exists.

A yellow change interval for the left-turn movement shall not be displayed when the status of the left-turn operation is changing from permissive to protected within any given signal sequence.

If the operating mode changes among the protected only mode and/or the protected/permissive mode and/or the permissive only mode during different periods of the day or as traffic conditions change, the requirements in EPG 902.5.24 through 902.5.26 that are appropriate to that mode of operation shall be met, subject to the following:

A. The CIRCULAR GREEN and CIRCULAR YELLOW signal indications shall not be displayed when operating in the protected only mode.

B. The left-turn GREEN ARROW and steady left-turn YELLOW ARROW signal indications shall not be displayed when operating in the permissive only mode.

Option. Additional static signs or changeable message signs may be used to meet the requirements for the variable left-turn mode or to inform drivers that left-turn green arrows will not be available during certain times of the day.

Support. EPG 902.X.XX through 902.X.XX describe the use of separate signal faces for controlling left-turn movements.

Separate left-turn signal face controls only the left-turn movement and cannot serve as one of the two required primary signal faces for the adjacent movement (usually the through movement) because it displays signal indications that are applicable only to the left-turn movement. If a separate left-turn signal face is mounted overhead at the intersection, it is positioned over the extension of the left-turn lane. In a separate left-turn signal face, a flashing left-turn YELLOW ARROW signal indication is used to control permissive left-turning movements.

EPG 902.5.19 contains provisions regarding the lateral positioning of signal faces that control left-turn movements.

It is not necessary that the same mode of left-turn operation or same type of left-turn signal face be used on every approach to a signalized location. Selecting different modes and types of left-turn signal faces for the various approaches to the same signalized location is acceptable.

Option. A signal face that is shared by left-turning and right-turning traffic may be provided for a shared left-turn/right-turn lane on an approach that has no through traffic (see EPG 902.5.35).

Support. Guidelines are available to aid in determining the proper left turn phasing for signalized intersections.

Left Turn Phasing Warrants

Left turn indications at signalized intersections are designed so they are neither overly restrictive nor inconsistent from the driver's point of view. The Left Turn Phasing Warrants are available in an interactive spreadsheet for safety warrants and capacity warrants to determine the amount of protection to be given to a left turn movement. These warrants are based upon accepted safety and capacity values for signalized intersections.

When factors such as sight distance, speed of opposing vehicles, etc. make permissive turns undesirable, the permissive left turn option is removed. Safety warrants are checked first; if an approach requires protected-only phasing for safety reasons, it is unnecessary to check the capacity warrants.

Once safety considerations are satisfied, Capacity Warrants will need to be analyzed. Capacity Warrants are divided into three parts: Permissive-Only left turns, Protected/Permissive left turns, and Protected-Only left turns. This criterion is used when designing or upgrading a signal installation.

In order to provide the proper phasing at an intersection, it will be necessary to check Capacity Warrants for several hours for each approach. For example, if only the peak hour is checked, the phasing will most likely be too restrictive for the rest of the day. It is recommended that the peak periods plus a sample of off-peak hours be checked before choosing the phasing.

When traffic volumes at an intersection are approaching the thresholds listed in the capacity warrants variable left turn phasing can be used by time of day. Variable left turn phasing allows for the selection of either protected only, protected/permissive, or permissive only left turn phasing. This can be used to provide appropriate phasing for varying volumes throughout the day. The protected left turn phase can be omitted by time of day and flashing yellow arrow operation allows for removal of the permissive left turn in addition to removal of the protected left turn phase. It can be used only on approaches with “positive” signal lane control, in that each approach lane has its own signal indication. Refer to EPG 902.X.XX for more information on flashing yellow arrow indications. Otherwise, the most appropriate left turn phasing is chosen based on the results of the Capacity Warrants.

When the flashing yellow arrow indication is used to provide variable phasing, each hour during a typical day is evaluated to determine proper phasing throughout the day. The Variable Left Turn Worksheet can help evaluate each hour during the day. During initial installation the flashing yellow arrow indication can allow the selection of more restrictive phasing initially and then change to a less restrictive mode if appropriate.

Note that some overlap may occur when analyzing the volumes at each approach (i.e., the data for one hour might satisfy parts of the criteria for both permissive-only and protected/permissive left turns). Therefore, it will be necessary to check at least two of the three parts of the criteria. When an overlap does occur, previous experience and/or evaluation studies at the location is to indicate whether the situation is better served by the more or less restrictive phasing that is determined using the criteria.

The left turn phasing guidelines, below, give safety and capacity considerations for selecting left turn phasing. The interactive spreadsheet allows for the user to directly enter criteria and see suggested thresholds based on these formulas. These guidelines are used when reviewing design plans and when modifying the phasing of an existing installation.

Guidance. Guidelines for Variable Left-Turn Phasing

This is a guide for the selection of variable left turn phasing hour-by-hour. Guidelines based on safety and capacity are provided.

Definition of Terms

The following terms are used in these guidelines :

VLT = The left turn volume per hour per approach.

(VLT)pp = The number of vehicles attempting to make permissive left turns during the permissive part of a protected/permissive left turn per hour per approach.

VO = The opposing volume per hour per approach per lane (excluding free right turn volume and volume serviced by a separate right turn phase).

cp = The cycle length (in seconds) when those volumes occur using permissive-only phasing¹.

cpp = The cycle length (in seconds) when those volumes occur using protected/permissive phasing¹.

gp = The green time (in seconds) common to both VLT and VO during that cycle using permissive-only phasing¹.

gpp = The green time (in seconds) common to both (VLTLT)pp and VO during that cycle using protected/permissive phasing¹.

TP = The time allocated to the protected left turn movement using protected/permissive phasing¹.

¹ These green times are used in the calculations regardless of the existing phasing. For phasing configurations not currently used it will be necessary to develop realistic timing for that phasing configuration. A signal timing computer program can be helpful in developing this timing.

Adjustment of Left Turn Volumes

This evaluation considers the number of vehicles attempting to make permissive left turns during the permissive part of a protected/permissive left turn. Therefore, the effects of protected left turns should be eliminated. This can be handled using the following method:

(VLT)pp = VLT - VP,

where the variable VP is the number of left turn vehicles served by the protected left turn indication. If this formula yields a negative number, use 0 for (VLT)pp. Assuming that vehicles enter the intersection at a rate of 2 seconds/vehicle, the volume using the protected movement in a one-hour period is:

VP = $\frac{T_p(sec/cycle)\times 3600(sec/hr)}{2(sec/vehicle)\times c_{pp}(sec/cycle)}$

Safety Criteria

Protected Only Left Turns

Protected-Only left turns shall be provided full-time when the number of opposing lanes ≥ 4.

Note: If the number of opposing lanes = 3, protected/permissive should be considered using engineering judgment.

The following factors should be considered when counting the number of opposing lanes crossed by left-turning traffic:

Through Lanes. Any lane in which through traffic is permitted shall be counted, even if turns are also permitted from that lane.

Left-Turn Lanes. Opposing exclusive left-turn lanes should usually not be counted, because typically opposing left turns do not conflict with each other.

Right-Turn Lanes. It may be acceptable to exclude opposing right-turn lanes. Omitting right-turn lanes is particularly appropriate where the right-turn movement is physically channelized from opposing through lanes and not under signal control. It may be desirable to include right-turn lanes in the count of opposing lanes where right-turn volume is heavy or where conflicts with left-turns are unusually high.

Protected-Only left turns should be provided full-time when any one of the following criteria are satisfied:

A. Sight Distance:

< 200 ft. for 25 mph

< 240 ft. for 30 mph

< 280 ft. for 35 mph

< 320 ft. for 40 mph

< 360 ft. for 45 mph

< 400 ft. for 50 mph

< 440 ft. for 55 mph

B. Number of Correctable Crashes By Upgrading to Protected Only Phasing > 5 over 12 months

Note: The correctable crashes should involve the SAME Left Turn approach. Only those approaches satisfying that criteria should be upgraded.

C. Number of Observed Traffic Conflicts > 48 Conflicts / 11 Hour Day

Note: Conflicts occur when motorists on the OPPOSITE APPROACH must respond to the actions of motorists making the subject left-turn movement. Therefore, conflicts should be measured by observing the intersection from the opposite approach. Only those approaches satisfying the criteria should be upgraded.

D. Speed (prevailing)

≥ 50 mph AND ≥ 2 opposing through lanes

= 45 mph AND a study indicates that the number of gaps is insufficient to turn safely

E. ≥ 2 left turn lanes.

Note: If there are two left turn lanes and one opposing through lane with low speed and low volume, protected/permissive might be considered using engineering judgment.

F. Unusual intersection geometrics that make permissive left turns difficult.

Protected/Permissive Left Turns

Note: Protected/Permissive left turns should be provided when the following criteria is satisfied.

A. Number of Observed Traffic Conflicts > 29 Conflicts / 11 Hour Day

Note: The number of conflicts are those occurring on the OPPOSITE APPROACH that are caused by the subject left-turn movement. Only those approaches satisfying the criteria should be upgraded.

Capacity Criteria

Permissive-Only Left Turns

Note: Permissive-Only left turns are an option when one of the criteria in (A.) is satisfied in conjunction with (B.).

A. VLT < 100 Vehicles per Hour

VLT < 2 Vehicles per Cycle¹

VO < 100 Vehicles per Hour

¹ This criteria is only valid if observations at the intersection show that drivers tend to make left turns during the clearance interval on a regular basis. These field checks should be made during the hour(s) in which either the highest left turn volume or the highest opposing volume occurs.

B. VLT + VO < 600 x (gp/cp)

Protected/Permissive Left Turns

Note: Protected/Permissive left turns should be provided when one of the criteria in (A.) is satisfied in conjunction with one of the criteria in (B.).

A. VLT > 100 Vehicles per Hour AND VO > 100 Vehicles per Hour

VLT > 2 Vehicles per Cycle¹ AND VO > 100 Vehicles per Hour

VLT + VO > 600 x (gp/cp)

¹ This criteria is only valid if observations at the intersection show that drivers tend to make left turns during the clearance interval on a regular basis. These field checks should be made during the hour(s) in which either the highest left turn volume or the highest opposing volume occurs.

B. (VLT)pp + VO < 1200 x (gpp/cpp)

(VLT)pp x VO < 50,000

Protected-Only Left Turns

Note: Protected-Only left turns should be provided when any one of the following criteria are satisfied.

A. (VLT)pp + VO > 1200 x (gpp/cpp) for 3 or more hours if considering permanent phasing change

B. (VLT)pp x VO> 50,000 for 3 or more hours if considering permanent phasing change

Protected left turn movements should be provided with an adequate turn bay or a separate turning lane, depending upon the volumes using the intersection and the existing intersection geometry. Protected-Only left turns should not be used with shared lanes unless split phase operation is used.

902.1.12 Change Period Equation

Change Period:
$CP=t+\frac{V}{2a+64.4g}+\frac{W+L}{V}$

Guidance:

CP = nondilemma change period (yellow plus all red), seconds

t = perception-reaction time, recommended as 1.0 second

V = approach speed (recommended as 85ᵗʰ or 15ᵗʰ percentile speed), ft/sec

g = percent grade (positive for upgrade, negative for downgrade), expressed as a decimal

a = deceleration rate, recommended as 10 ft/sec²

W = width of intersection from stop line to end of far side crosswalk (if present), ft

L = length of vehicle, recommended as 20 ft