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TDOT TRAFFIC DESIGN MANUALJUNE 2020CHAPTER 13OTHER TYPES OF TRAFFIC SIGNALS13.1 Highway Traffic SignalsThe primary type of traffic signal device in use is the traditional traffic control signal atan intersection (See Chapters 5-12 in this manual for details on traditional traffic controlsignals). However, a traffic signal can be a device other than a traditional traffic controlsignal. The following are additional types of traffic signals: Pedestrian Hybrid Beacons (MUTCD Chapter 4F): A pedestrian hybrid beaconis a special type of hybrid beacon used to warn and control traffic at anunsignalized location, in order to assist pedestrians in crossing a street orhighway at a marked crosswalk. Pedestrian hybrid beacons are also known as“HAWK Signals”. Emergency Vehicle Traffic Control Signals (MUTCD Chapter 4G): A specialtraffic control signal that assigns the right-of-way to an authorized emergencyvehicle. Traffic Control Signal for One-Lane, Two-Way Facilities (MUTCDChapter 4H): A traffic control signal for one-lane, two-way facilities, such as anarrow bridge, tunnel, or roadway section, and is a special signal that assigns theright-of-way for vehicles passing over a bridge or through a tunnel or roadwaysection that is not of sufficient width for two opposing vehicles to pass. Ramp Control Signal (MUTCD Chapter 4I): A highway traffic signal installed tocontrol the flow of traffic entering the freeway facility. This is often referred to as“ramp metering”. Traffic Control for Movable Bridges (MUTCD Chapter 4J): A special type ofhighway traffic signal installed at movable bridges to notify road users to stopbecause of a road closure rather than alternately giving the right-of-way toconflicting traffic movements. Traffic Signals at Toll Plazas (MUTCD, Chapter 4K): Traffic control signalsused at toll booth plazas. Flashing Beacons (MUTCD Chapter 4L): A highway traffic signal with one ormore signal sections that operates in a flashing mode. Lane-Use Control Signals (MUTCD Chapter 4M): A signal face displayingsignal indications to permit or prohibit the use of specific lanes of a roadway or toindicate the impending prohibition of such use. In-Roadway Lights (MUTCD Chapter 4N): In-roadway lights are special typesof highway traffic signals installed in the roadway surface to warn road users thatthey are approaching a condition on or adjacent to the roadway that might not bereadily apparent and might require the road users to slow down and/or come to astop. This includes situations warning of marked school crosswalks, markedmidblock crosswalks, marked crosswalks on uncontrolled approaches, marked13 - 1
TDOT TRAFFIC DESIGN MANUALJUNE 2020crosswalks in advance of roundabouts, and other roadway situations involvingpedestrian crossings.The next sections summarize important information on the other types of traffic signalslisted above that are relevant in Tennessee.13.2 Pedestrian Hybrid BeaconsGenerally, a pedestrian hybrid beacon is considered for installation to facilitatepedestrian crossings at a location that does not meet traffic signal warrants. When anengineering study finds that installation of a pedestrian hybrid beacon is justified, then: At least two pedestrian hybrid beacon faces shall be installed for each approachof the major street; A stop line shall be installed for each approach to the crosswalk; A pedestrian signal head conforming to the provisions set forth in the MUTCDChapter 4E shall be installed at each end of the marked crosswalk; and The pedestrian hybrid beacon shall be pedestrian actuated and shall conform tothe provisions set forth in the MUTCD Chapter 4F.Figure 13.1 presents a pedestrian hybrid beacon sequence display.Figure 13.1 – Pedestrian Hybrid Beacon Sequence Display13 - 2
TDOT TRAFFIC DESIGN MANUALJUNE 202013.3 Emergency Vehicle Traffic Control SignalsAn emergency vehicle traffic control signal may be installed at a location that does notmeet other traffic signal warrants, such as at an intersection or other location to permitdirect access from a building housing the emergency vehicle (e.g. fire station).13.3.1 DisplaysThe emergency signal shall display either steady green or flashing yellow to thepublic street approaches when not activated. If the flashing yellow signalindication is used instead of the steady green signal indication, it shall bedisplayed in the normal position of the steady green signal indication; while thered and steady yellow signal indications shall be displayed in their normalpositions. When an emergency vehicle actuation occurs, a steady yellow changeinterval followed by a steady red interval shall be displayed to traffic on the publicstreet. An emergency vehicle hybrid beacon may be installed instead of anemergency traffic control signal under specific conditions (MUTCD Section4G.04). Figure 13.2 presents an emergency hybrid beacon sequence display.13.3.2 ControlAn emergency vehicle traffic control signal sequence may be initiated manuallyfrom a local control point, such as a fire station or police headquarters, or from anemergency vehicle equipped for remote operation of the signal.13.3.3 SigningIf an emergency signal is used, the following signs shall be installed: An Emergency Vehicle (W11-8) sign with an Emergency Signal Ahead(W11-12P) supplemental plaque shall be placed in advance of anemergency vehicle signal. A warning beacon may be installed tosupplement the Emergency Vehicle sign; and An Emergency Signal (R10-13) sign shall be mounted adjacent to a signalface on each street approach.13 - 3
TDOT TRAFFIC DESIGN MANUALJUNE 2020Figure 13.2 – Emergency Vehicle Traffic Signals13 - 4
TDOT TRAFFIC DESIGN MANUALJUNE 202013.4 Flashing BeaconsA flashing beacon is composed of one or more traffic signal sections operating in aflashing mode. A flashing beacon can provide traffic control when used as anintersection control beacon, or it can provide warning, as described below. An automaticdimming feature may be used to reduce the nighttime brightness.13.4.1 Intersection Control BeaconsIntersection control beacons consist of two signal faces per intersectionapproach, each with one signal section having a 12-inch lens (See Figure 13.3).Normally, flashing yellow signal indications will be displayed to the major streetand flashing red signal indications to the minor street. At the intersection of twostreets of equal importance, flashing red signal indications may be displayed toboth streets. A Stop sign shall be used on approaches to which a flashing redsignal indication on an intersection control beacon is shown. If two horizontallyaligned red signal indications are used on an approach for an intersection controlbeacon, they shall be flashed simultaneously to avoid being confused with gradecrossing flashing-light signals. If two vertically aligned red signal indications areused on an approach for an intersection control beacon, they shall be flashedalternately. Intersection control beacons are intended to be used as asupplement to and not a replacement for other traffic control devices at theintersection. An intersection beacon may be installed when conditions do notjustify the installation of a conventional traffic signal, but crash rates indicate thepossibility of a special need. The most common application for these beacons isat intersections with minor approach stop control, where some approachingvehicles on the controlled legs have failed to stop.13.4.2 Stop Beacons (Red)A stop beacon shall be used only to supplement a Stop sign, a Do Not Entersign, or a Wrong Way sign. Stop sign beacons consist of one or more signalsections having flashing red 12-inch signal indications mounted on a Stop sign(See Figure 13.3). If two flashers are used on one sign, they shall flashsimultaneously if mounted horizontally and alternately if mounted vertically. Stopbeacons can be justified for Stop signs subject to the following considerations: Violations: A significant number of vehicles violate the stop condition. Crashes: A crash rate exists that indicates the presence of a specialneed.13.4.3 Speed Limit Sign BeaconsA speed limit sign beacon consists of one or more signal sections with a flashingcircular yellow signal indication in each section. It is used to supplement a SpeedLimit sign. It may be installed with a fixed or variable Speed Limit sign (R2-1)where studies show a need to emphasize that a speed limit is in effect. Signalindications may be either 8-inch or 12-inch and they shall flash alternately.13 - 5
TDOT TRAFFIC DESIGN MANUALJUNE 2020Figure 13.3 – Intersection Control Beacons and Stop Beacons (Red)13 - 6
TDOT TRAFFIC DESIGN MANUALJUNE 202013.4.4 School Zone Speed Limit Sign BeaconsA school zone flashing beacon consists of two signal sections with a flashingcircular yellow signal indication in each section and is used in conjunction withthe standard School Zone sign (S5-1) (See TDOT Standard Drawing T-SG-13).Figure 13.4 displays the typical layout. Eight-inch lenses may be used andinstalled within the borders of the sign. When 12-inch signal heads are used, theymust be mounted on the outside of the sign. The two indications in a school zonespeed limit beacon shall flash alternately. A school zone beacon may be installedand maintained by a school board or local government at an established schoolzone under a Traffic Control Device Permit. School zone beacons on Statehighways must be coordinated through the TDOT Regional Traffic Engineer.13.4.5 Warning Beacons (Yellow)Warning beacons are used only to supplement an appropriate warning orregulatory sign or marker (See Figure 13.5). Warning beacons consist of one ormore signal sections, each having flashing yellow signal indications which flashalternately. Warning beacons may be justified by either of the following: Obstruction Identification: Warning beacons may be used to helpidentify obstructions in or immediately adjacent to the roadway wherecrash experience indicates that additional emphasis is needed tosupplement existing signing and pavement markings. Such obstructionscould include guardrail at T-intersections, bridge supports in or near theroadway, etc. Supplement to Advance Warning Signs: A flashing beacon may beused to supplement advance warning signs for a variety of conditions,where crash experience or field observation reveals that the warning signsalone are not effective. Such conditions could include sharp curves,obscured stop conditions, weather-related hazards such as fog and ice,obscured railroad crossings, truck crossings, plant entrances, etc.Warning beacons are also applicable to emphasize midblock crosswalks.13.4.6 Traffic Signal Ahead BeaconsTraffic signal ahead beacons consist of one or more signal sections, each havingalternately flashing yellow signal indications (See Figure 13.5). They are used inconjunction with the standard Signal Ahead warning sign (W3-3). Signal aheadbeacons may be justified under either of the following conditions: First Signal: On highways with a posted speed limit 45 mph or greaterthat is approaching the first signalized intersection of a community ortown, and the intersection experiences a crash rate that indicates thepresence of a special need. Sight Distance: On highways with a posted speed limit 45 mph or greaterthat is approaching a traffic signal whose signal visibility is less than thatcalled for in Table 9.2 (Minimum Sight Distance for Signal Visibility).13 - 7
TDOT TRAFFIC DESIGN MANUALJUNE 2020Figure 13.4 – School Zone Speed Limit Sign Beacons13 - 8
TDOT TRAFFIC DESIGN MANUALJUNE 2020Figure 13.5 – Warning Beacons (Yellow) and Traffic Signal Ahead Beacons13 - 9
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The primary type of traffic signal device in use is the traditional traffic control signal at an intersection (See Chapters 5-12 in this manual for details on traditional traffic control signals). However, a traffic signal can be a device other than a traditional traffic control signal. The following are additional types of traffic signals:
