902.12 Flashing Beacons (MUTCD Chapter 4L)

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902.12.1 General Design and Operation of Flashing Beacons (MUTCD Section 4L.01)

Support. A Flashing Beacon is a highway traffic signal with one or more signal sections that operates in a flashing mode. It can provide traffic control when used as an intersection control beacon (see EPG 902.12.2) or it can provide warning when used in other applications (see EPG 902.12.3 through EPG 902.12.5).

When used with good judgment, the installation of a flashing beacon can be an extremely effective traffic control device. However, indiscriminate use degrades their effectiveness and affects the usefulness of other flasher installations. Flashing beacons can be installed by MoDOT or by outside parties. An engineering study is to be performed to determine the need for them.

Flashing beacons can be used in a number of different applications. The installation of flashing beacons at any location on the State Highway System is to be approved by the District Engineer. Likewise, the removal of any flashing beacons installed by MoDOT over any roadway shall also have prior approval from the District Engineer.

A number of flashing beacons present on state highways were installed and are operated by others. No concerted attempt to have them removed is to be engaged in except when such a flasher is considered a potential safety problem to the motoring public, or conditions have changed so a flasher is no longer needed. If these conditions occur, the organization operating the flasher is to be encouraged to remove it. However, if its operation is considered to be important to traveler safety, consideration is to be given for MoDOT to assume responsibility for operating and maintaining the flasher.

Standard. Flashing Beacon units and their mountings shall comply with the provisions of EPG 902.5, except as otherwise provided in this article.

Beacons shall be flashed at a rate of not less than 50 or more than 60 times per minute. The illuminated period of each flash shall be a minimum of 1/2 and a maximum of 2/3 of the total cycle.

A beacon shall not be included within the border of a sign except for SCHOOL SPEED LIMIT sign beacons (see EPG 902.12.4 and MUTCD Section 7B.15).

Guidance. If used to supplement a warning or regulatory sign, the edge of the beacon signal housing should normally be located no closer than 12 in. outside of the nearest edge of the sign.

Option. An automatic dimming device may be used to reduce the brilliance of flashing yellow signal indications during night operation.

902.12.2 Intersection Control Beacon (MUTCD Section 4L.02)

Standard. An Intersection Control Beacon shall consist of one or more signal faces directed toward each approach to an intersection. Each signal face shall consist of one or more signal sections of a standard traffic signal face, with flashing CIRCULAR YELLOW or CIRCULAR RED signal indications in each signal face. They shall be installed and used only at an intersection to control two or more directions of travel.

Application of Intersection Control Beacon signal indications shall be limited to the following:

A. Yellow on one route (normally the major street) and red for the remaining approaches, and
B. Red for all approaches (if the warrant described in EPG 903.5.4.3 for a multi-way stop is satisfied).

Flashing yellow signal indications shall not face conflicting vehicular approaches.

A STOP sign shall be used on approaches to which a flashing red signal indication is displayed on an Intersection Control Beacon (see MUTCD Section 2B.04).

If two horizontally aligned red signal indications are used on an approach for an Intersection Control Beacon, they shall be flashed simultaneously to avoid being confused with grade crossing flashing-light signals. If two vertically aligned red signal indications are used on an approach for an Intersection Control Beacon, they shall be flashed alternately.

All intersection control beacons shall be installed and/or maintained to provide a clearance over the roadway of 16 ft. to 19 feet.

A pole on state right of way owned by others shall not be used to support a span wire flasher. If an adjustment of the location for a department installed pole cannot be made, the existing pole shall be moved at the expense of the owner.

Hybrid beacons (pedestrian and emergency) are not considered an intersection control beacon and are not subject to provisions stated in the section. Refer to EPG 902.6 and EPG 902.7 for provisions for pedestrian and emergency hybrid beacons, respectively.

Guidance. An Intersection Control Beacon should not be mounted on a pedestal in the roadway unless the pedestal is within the confines of a traffic or pedestrian island.

Option. Where there are two or more approach lanes, it is desirable to center a head over each lane; however, one head per approach is acceptable.

Guidance. Conditions for which intersection beacons should be considered are:

  • A required stop after a long period of uninterrupted speed,
  • A required stop on a long tangent section of roadway where cross-street traffic may have trouble judging the distance and speed of an oncoming vehicle,
  • A stop condition not readily visible to the approaching driver,
  • A situation where traffic on the major roadway may not be aware of cross-street traffic.

Standard. When an overhead flasher is authorized for installation at an intersection, the support pole shall be placed in accordance with the AASHTO Roadside Design Guide clear zone guidelines.

Typical Flasher Layouts
Typical Flasher Layouts

Option. Supplemental signal indications may be used on one or more approaches in order to provide adequate visibility to approaching road users.

Intersection Control Beacons may be used at intersections where traffic or physical conditions do not justify conventional traffic control signals but crash rates indicate the possibility of a special need.

An Intersection Control Beacon is generally located over the center of an intersection; however, it may be used at other suitable locations.

902.12.3 Warning Beacon (MUTCD Section 4L.03)

Support. Typical applications of Warning Beacons include the following:

  • A. At obstructions in or immediately adjacent to the roadway;
  • B. As supplemental emphasis to warning signs;
  • C. As emphasis for midblock crosswalks;
  • D. As supplemental emphasis to regulatory signs, except STOP, DO NOT ENTER, WRONG WAY and SPEED LIMIT signs (see EPG 902.12.4 Speed Limit Sign Beacons) ; and
  • E. In conjunction with a regulatory or warning sign that includes the phrase WHEN FLASHING in its legend to indicate that the regulation is in effect or that the condition is present only at certain times.

Standard. A Warning Beacon shall consist of one or more signal sections of a standard traffic signal face with a flashing CIRCULAR YELLOW signal indication in each signal section. A Warning Beacon shall be used only to supplement an appropriate warning or regulatory sign or marker.

Warning Beacons, if used at intersections, shall not face conflicting vehicular approaches.

If a Warning Beacon is suspended over the roadway, the clearance above the pavement shall be a minimum of 16 ft. and a maximum of 19 feet.

Guidance. The condition or regulation justifying Warning Beacons should largely govern their location with respect to the roadway.

If an obstruction is in or adjacent to the roadway, illumination of the lower portion or the beginning of the obstruction or a sign on or in front of the obstruction, in addition to the beacon, should be considered.

Warning Beacons should be operated only during those periods or times when the condition or regulation exists.

Option. Warning Beacons that are actuated by pedestrians, bicyclists, or other road users may be used as appropriate to provide additional warning to vehicles approaching a crossing or other location.

If Warning Beacons have more than one signal section, they may be flashed either alternately or simultaneously.

A flashing yellow beacon interconnected with a traffic signal controller assembly may be used with a traffic signal warning sign (see MUTCD Section 2C.36).

Warning beacons may be installed in conjunction with school advance signing or in conjunction with a school speed limit assembly at the request of the school district and at their cost.

Warning beacons may be installed in conjunction with emergency vehicle advance signing at the request of the emergency vehicle service district and at their cost.

Standard. School warning beacons only operate when there is activity at the school or school crossing. When school speed limit signing is installed, beacons shall be installed with the signing. The beacons are only activated at times when the school speed limit applies.

Emergency vehicle warning beacons are set up to operate only when emergency vehicles are exiting the station or garage on a duly authorized emergency run. As with the school beacons, these beacons enhance the meaning of the advanced signing by only flashing when emergency activity is occurring.

See EPG 902.12.7 Procedures For Advance Beacon Installations by Outside Parties for additional information regarding school and emergency vehicle warning beacons.

902.12.4 Speed Limit Sign Beacon (MUTCD Section 4L.04)

Standard. A Speed Limit Sign Beacon shall be used only to supplement a Speed Limit sign.

A Speed Limit Sign Beacon shall consist of one or more signal sections of a standard traffic control signal face, with a flashing CIRCULAR YELLOW signal indication in each signal section. The signal indications shall have a nominal diameter of not less than 12 inches. If two signal indications are used, they shall be vertically aligned. If two signal indications are used, they shall be alternately flashed.

If used, the phrase WHEN FLASHING is required to be in the legend or on a supplemental plaque.

Option. A Speed Limit Sign Beacon may be used with a fixed or variable Speed Limit sign. If applicable, a flashing Speed Limit Sign Beacon (with an appropriate accompanying sign) may be used to indicate that the displayed speed limit is in effect.

A Speed Limit Sign Beacon may be included within the border of a School Speed Limit (S5-1) sign (see MUTCD Section 7B.15).

902.12.5 Stop Beacon (MUTCD Section 4L.05)

Standard. A Stop Beacon shall be used only to supplement a STOP sign, a DO NOT ENTER sign, or a WRONG WAY sign.

A Stop Beacon shall consist of one or more signal sections of a standard traffic signal face with a flashing CIRCULAR RED signal indication in each signal section. If two horizontally aligned signal indications are used for a Stop Beacon, they shall be flashed simultaneously to avoid being confused with grade crossing flashing-light signals. If two vertically aligned signal indications on the same structure are used for a Stop Beacon, they shall be flashed alternately.

If mounted above a STOP sign, a DO NOT ENTER sign, or a WRONG WAY sign the bottom of the signal housing of a Stop Beacon shall be not less than 12 in. or more than 24 in. above the top of the sign. If mounted below a STOP sign, a DO NOT ENTER sign, or a WRONG WAY sign the top of the signal housing of a Stop Beacon shall be not less than 12 in. or more than 24 in. (only used when an additional sign is used below, i.e. Divided Highway, All Way, etc.) below the bottom of the sign.

902.12.6 Interactive Flashing Beacons

Option. Types of interactive flashing beacons may be any of the previously mentioned types of beacons. These beacons may be accompanied with signs that reinforce the message. Examples include: beacons activated by approaching traffic or excessive speed, beacons used to give advance warning of a yellow change interval at a signalized intersection or beacons used to notify motorists of traffic stopped ahead. Beacons activated by approaching traffic may be used where sight distance is limited and cross-street traffic may have trouble judging the distance and speed of approaching traffic. Beacons activated when motorists exceed a posted speed may be used where conditions require a reduction in traffic speed. Examples of this use include low speed curves or where drivers regularly exceed the posted speed limit. Beacons activated a few seconds before (or at the start of) the yellow change interval at a signalized intersection may be used to give high speed traffic advance warning of the signal changing from green to yellow.

Standard. Interactive flashing beacons shall be activated only when required.

902.12.7 Procedures For Advance Beacon Installations by Outside Parties

Standard. Advance beacons such as: school warning, school speed limit, and emergency vehicle warning beacons are installed under contract. The district will obtain appropriate signed contracts to be sent to Central Office Traffic for further handling. These contracts deal with the installation and transfer of ownership of the installation from the outside party to the Commission.

Support. The following standard contracts are available:

See EPG 902.17 Execution of Contracts for Signal or Flasher Installation for additional information on execution of contracts.

Standard. Plans for installation shall be the responsibility of the outside party and shall conform to the latest standards of MoDOT.

Once the contract is executed, a permit to work on MoDOT’s right-of-way shall be obtained by the outside party. Once issued, the outside party may proceed to install the beacons. A contractor or the outside party shall complete the installation; however, a licensed electrician shall supervise the installation.

Layouts are illustrated in Fig. 902.11 Advanced Flasher Figures and equipment listed in Appendix.

With the exception of the signs and mounting brackets supplied by MoDOT, all costs shall be the responsibility of the outside party. This includes but is not limited to installation and power.

Beacons shall be active only during those times when the conditions of the advanced signing are applicable or when the enhancement of the signed message is needed. The times of operation, timing, and method of operation are approved by MoDOT.

MoDOT will maintain installations and equipment unless otherwise indicated in the contract. Power costs after transfer of ownership to MoDOT and any other equipment off right of way are the responsibility of the outside party.

Flashing beacons shall only be installed on advanced signing and shall not be installed at the condition applicable to the advanced signing.

Only one flasher shall be permitted per approach.

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