Traffic Manual: Chapter 9
Chapter 9 - Traffic Signals and Lighting
- 9-00 - Table of Contents, List of Figures and List of Tables
- 9-01 - Traffic Signals, Basic Information and Warrants
- 9-02 - Traffic Signal Development Procedures
- 9-03 - Traffic Signal Design
- 9-04 - Traffic Signal Opeations
- 9-05 - Flashing Beacons
- 9-06 - Highway Safety Lighting
- 9-07 - Freeway Lighting
- 9-08 - Conventional Highway Lighting
- 9-09 - Highway Safety Lighting Design Procedures
- 9-10 - Highway Safety Lighting Design Standards
- 9-11 - Lighting Standards
- 9-12 - Luminaires
- 9-13 - Conduit, Wiring and Circuits
- List of Chapter 9 Figures
- List of Chapter 9 Tables
Section 9-00 - Table of
Contents, List of Figures and List of Tables
Table of contents listing for Sections 9-01 through 9-05 have been intentionally removed,
visit Part 4 of the CA MUTCD for guidance.
9-06 Highway Safety Lighting
9-07 Freeway Lighting
9-08 Conventional Highway Lighting
9-09 Highway Safety Lighting Development Procedures
9-10 Highway Safety Lighting Design Standards
9-11 Lighting Standards
9-13 Conduit, Wiring and Circuits
List of Figures:
|View JPEG file||or PDF file||Figure 9-25 Freeway Lighting|
|View JPEG file||or PDF file||Figure 9-26 Freeway Lighting|
|View JPEG file||or PDF file||Figure 9-27 Intersection Lighting|
|View JPEG file||or PDF file||Figure 9-28 Intersection Lighting|
List of Tables:
|View JPEG file||or PDF file||Table 9-8 Available Conduit Area (Square Millimeters)|
|View JPEG file||or PDF file||Table 9-9 Conductor Size|
Section 9-01, Traffic Signals, Basic Information and Warrants, visit Part 4 of the CA MUTCD for guidance.
Section 9-02, Traffic Signal Development Procedures, visit Part 4 of the CA MUTCD for guidance.
Section 9-03, Traffic Signal Design, visit Part 4 of the CA MUTCD for guidance.
Section 9-04, Traffic Signal Operations, visit Part 4 of the CA MUTCD for guidance.
Section 9-05, Flashing Beacons, visit Part 4 of the CA MUTCD for guidance.
Section 9-06 - Highway Safety Lighting
The purpose of highway safety lighting is to promote the safe and orderly movement of traffic by illuminating certain permanent features or conditions which are unusual, which require additional care and alertness to negotiate, and which, if illuminated, may be more readily comprehended and so compensated for by the motorist.
Section 9-07 - Freeway Lighting
On freeways, highway safety lighting should be installed at particular points in interchange areas. This lighting serves to illuminate areas of potential vehicle conflict and to delineate exit ramps, entrance ramps, and island noses.Except where required by unusual freeway geometrics, lighting should not be installed unless the traffic volumes shown in Section 9-07.2 are met. The high standard of signing, markings, and delineation now being provided makes it possible in such situations to defer the installation of lighting facilities until required by increased traffic.The use of high mast lighting systems may be considered where conventional lighting standards are difficult to maintain.
1. Definitions.2. Freeway Interchange Safety Lighting.
a. Urban, Suburban and Rural Conditions. Urban conditions are considered to exist in those areas so designated on maps approved by the FHWA. Suburban conditions are considered to exist in those areas contiguous to the designated urban areas. Rural conditions exist in all other areas.
b. ADT is the average daily traffic for up to five years after the freeway is opened to traffic.
c. A surface street is any street other than a freeway. A local street is a surface street under the control of a local agency.Freeway Interchange safety lighting is considered to be warranted under either of the following conditions:3. Freeway Ramp-Surface Street Intersection Safety Lighting.
a. Where the total sum of the ADT ramp traffic entering and leaving the freeway within the interchange area exceeds 5,000 under urban conditions, 3,000 under suburban conditions and 1,000 under rural conditions. The above figures refer to the total sum of the ADT for the normal four ramps at an interchange. Where the number of ramps connecting with the freeway is less than four, the above total sum of ADT may be reduced proportionately.
b. Where the ADT on the freeway exceeds 25,000 for urban conditions, 20,000 for suburban conditions and 10,000 for rural conditions.Safety lighting at the intersection of a freeway ramp and a surface street is considered warranted if either of the conditions in 2a or 2b above are satisfied.4. Lighting of Existing Local Streets Within the Limits of the Freeway Project.Lighting of existing local streets within the limits of a freeway project, including lighting on local streets over or under the freeway, is considered warranted if:5. Lighting of New Local Streets within the Limits of the Freeway Project.a. The local street is lighted to modern standards up to the freeway right of way and the local agency agrees to assume ownership and cost of maintenance; orb. The local street is not lighted to modern standards and the local agency agrees to assume ownership and all costs of installation and maintenance.If a local agency indicates that it proposes to install lighting on the local street within five years after construction is completed, the following should be installed on the project at 100% State expense:a. Conduit and other equipment in and under paved areas.b. Provisions for future structure lighting as stated in (7) below:The installation of lighting on new local streets, including new frontage roads, that are constructed on new alignment for a local agency shall be governed by the following:6. Lighting for Exclusive Pedestrian Facilities.
a. Lighting may be installed when requested by the local agency, only if there is existing lighting in the area and if that lighting is owned by the local agency. The lighting design and financing shall follow the guidelines in Section 9-09.7.
b. Where the existing lighting is owned by a private utility, only equipment that will be in or under paved areas shall be installed by the State. See Section 9-09.7.
c. If no lighting exists in the area, new lighting shall be installed only if the local agency agrees to finance the installation and to assume the cost of ownership and maintenance.The lighting for exclusive pedestrian facilities within the freeway project is considered warranted at the following locations:7. Freeway Structures Lighting.Lighting shall be provided on pedestrian overcrossings and undercrossings where the local agency agrees to assume ownership and cost of maintenance.Pedestrian undercrossings shall be provided with adequate daytime as well as nighttime illumination.
a. Separated walkways (not sidewalks) and crosswalks within the interchange areas.
b. Bicycle paths at roadway crossings and at underpasses.
c. Bus stops within the interchange areas.
d. Pedestrian overcrossings and undercrossings.8. Replacement of Lighting Owned by Other Agencies.
Lighting on or under a freeway structure is considered warranted if:Provision for future lighting may be installed in structures for freeway illumination only if there is a definite requirement to install lighting as warranted above in the future. Provision for future lighting consists of conduit, pull boxes, anchor bolts and flush soffit luminaires.
a. The lighting is for the purpose of illuminating acceleration lanes, deceleration lanes, weaving areas or walkways.
b. It is a part of local street lighting as stated in (4) or (5) above.See Section 9-09.79. Lighting for Ramps at Rest Areas and Truck Inspection Stations.Lighting on freeway acceleration and deceleration lanes at rest areas and truck weight and inspection stations shall be considered in the same manner as interchange ramps.
Section 9-08 - Conventional Highway Lighting
On conventional highways, including expressways, State financing of highway safety lighting shall be limited to that at intersections with traffic signals or flashing beacons or at those locations which meet the conditions listed below. The existence of an intersection is not, in itself, a justification for lighting.When highway safety lighting is to be installed at an intersection the "Basic" illumination as shown in Section 9-10.3 shall be provided.
1. Existing Intersections.Safety lighting may be provided at existing intersections on expressways and conventional highways if one of the following conditions is fulfilled:2. New Intersections.
a. A Minimum Vehicular Volume, an Interruption of Continuous Traffic or Minimum Pedestrian Volume traffic signal warrant (see Section 9-01.2) is satisfied for any single hour which may be in darkness in winter months.
b. Four or more nighttime accidents in any recent consecutive 12-month interval or six or more nighttime accidents in any recent consecutive 24-month interval.
c. Where a traffic signal or an intersection flashing beacon is installed.
d. Where combinations of sight distance, or horizontal or vertical curvature of the roadway, channelization or other factors constitute a confusing or unsatisfactory condition that may be improved with lighting. The project report covering such lighting should include an explanation of the factors constituting the confusing or unsatisfactory condition.Safety lighting may be provided at new intersections on expressways or conventional highways if there are indications that any of the warrants listed in 1(a) above will be fulfilled within five years after the opening of the project to traffic.3. Railroad Grade Crossings.Safety lighting may be provided at railroad grade crossings where a substantial amount of railroad operation is conducted at night, particularly where train speeds are low, where crossings are blocked for long periods, or a study indicates that motorists experience difficulty in seeing trains or traffic control devices during the hours of darkness.
Section 9-09 - Highway Safety Lighting Development Procedures
General requirements for the development of lighting projects are noted in the Project Development Procedures Manual. The cost of lighting on Federal Aid highway projects is eligible for federal participation under certain conditions. The Federal Highway Administration uses "An Information Guide for Lighting Controlled Access Highways" published by the American Association of State Highway and Transportation Officials to determine eligibility for participation on Interstate projects.The preparation of a Project Study Report may be required for lighting projects for scoping and programming purposes. The Project Development Procedures Manual and the appropriate Program Advisor should be consulted to determine specific reporting requirements.
The following data are required to appraise the need for highway safety lighting installation and should be included in the Project Report:
1. Traffic Counts.Both pedestrian and vehicular traffic counts shall be shown for any single hour which may be in darkness in winter months. Traffic counts shall be shown on Forms TS-10A, B and/or C. On Form TS-11 the single hour traffic count shall be the one during a period of darkness which shows the most need for the project. Show pedestrian volume on each crosswalk for the same periods as the vehicular count.2. Vehicle Speed.The 85th percentile speed of vehicles on approaches to the intersection.3. Electrical Service.A statement as to the availability of electrical service. Where the establishment of electrical service is excessively costly due to line extension, consideration should be given to alternate sources of power or to deferment of the installation.4. Other Data.This includes:
a. The location map;
b. A condition diagram showing existing conditions;
c. A summary of accidents and the collision diagram;
d. Form TS-10A, B and/or C;
e. Form TS-11;
f. An improvement diagram showing existing and proposed lighting, channelization, and other proposed improvements. This may be combined with (b), (c), (d), and (e) on a single plan;
g. An estimate of cost; and
h. An explanation of the confusing or unsatisfactory conditions to be improved by the lighting.
During the design stage, the local electrical utility should be contacted to determine the location and type of service available.
General requirements for the submittal of plans, specifications and estimates are noted in the Project Development Procedures Manual and the PS&E Guide. All electrical plans shall bear the following: "Note: This plan accurate for electrical work only."The Office of Structures Design shall forward a reproducible general plan of all structures to the District Traffic Engineer or the District Electrical Design Section. The District shall submit two prints showing requirements for conduits, foundations, and pull boxes to the Office of Structures Design for review and comment. Locations of illuminated sign structures shall also be noted. One print of each plan will be returned to the District with any necessary changes indicated thereon. After any necessary changes have been made, the revised plans shall be signed and forwarded with the PS & E Report.
1. General Policy.State participation in financing is based on the use of standard equipment in accordance with State plans and specifications. If local agencies desire to use more expensive equipment, the additional cost over the standard equipment shall be at 100% local agency expense except as noted below.2. Freeways.The cost of installing highway safety lighting on freeways is to be at 100% State expense. If other agencies desire to provide lighting between interchange areas, such lighting may be included in the Stateís project. However, the State will not participate in installation costs. The State will maintain and operate the lighting at 100% local agency expense.On Federal Aid projects, Federal participation will be requested when one or more of the traffic volume warrants in Section 9-07.2 are met.At the intersections of freeway ramps with local streets, the installation cost of safety lighting shall be at 100% State expense if it is found to be warranted at any time within five years after the date the freeway is opened to traffic. Lighting, which meets the warrants stated in Section 9-07.2, may be installed at State expense on new frontage roads and local streets constructed as a part of a freeway project when such lighting will be owned by a local agency. Lighting design may conform to the established design standards of the local agency.3. Existing Conventional Highway Intersections.Highway safety lighting to be installed at existing intersections shall be financed jointly by the State and the local agency in the same ratio as the number of legs under each jurisdiction bears to the total number of legs at the intersection.On a small project, where the prorated share of the local agency is $3000 or less, the cost shall be at 100% State expense.The District Director may approve the installation of warranted utility-owned safety lighting without submitting a Project Report to Headquarters.Normally, the monthly charges for utility-owned safety lighting installed at the request of the State should be shared jointly with the local agency, as above.4. New Conventional Highway Intersections.The installation cost of highway safety lighting at new intersections on a State highway as a result of a State highway project shall be at 100% State expense. The installation cost of highway safety lighting at new intersections on a State highway as a result of a local agency project shall be at 100% local agency expense.5. Railroad Crossings.The costs of installing and maintaining safety lighting at railroad grade crossings on State highways shall be at 100% State expense.
Where a local agency proposes to install lighting on a State highway, an encroachment permit is required. Lighting may also be installed at the intersection of a State highway and private driveway by a private property owner under an encroachment permit. Such lighting shall in no way detract from the effectiveness of existing State safety lighting or in any way interfere with the safe movement oftraffic. On existing roadways, except expressways or freeways, the lighting may be installed on wood poles with overhead wiring. On expressways and full freeways, the equipment shall meet State standards, i.e., steel standards and underground wiring. Where a local agency proposes to install continuous lighting using luminaires of higher light output than the existing highway safety luminaires, the project should include replacing the existing units with new luminaires with the higher light output. The State will review the design of such lighting. The installation may be performed by local agency forces, a contractor or an electrical utility.The State will participate only in the costs of installation or upgrading, maintenance, and operation of safety lighting as warranted in Sections 9-07.2 and 9-08.2.
1. FreewaysWhen affected by State freeway construction, existing street lighting facilities owned by a local agency shall be replaced in kind, as nearly as possible, at 100% State expense using salvaged material where feasible.In the event the local agency desires to have the relocated local agency owned lighting system reconstructed to an improved standard as part of a State contract, the difference in cost between replacement in kind and the construction requested shall be estimated and the agency shall agree to reimburse the State for the additional cost.The reconstruction of existing street lighting facilities owned by a private utility is the responsibility of the utility and will be handled by the Division of Right of Way. See Section 9-07.2(5b).2. Conventional HighwaysWhen affected by construction on a conventional State highway, existing street lighting facilities owned by a city, county, or lighting district shall be reconstructed at the sole expense of the owner unless prior rights can be established.In the event a local agency desires to have an existing continuous lighting system along a State highway reconstructed to an improved standard, or a new system built to higher than State standards, the cost to the State shall be limited to its share of the lighting at those locations where safety lighting is warranted.
Section 9-10 - Highway Safety Lighting Design Standards
The design of highway safety lighting by the California Department of Transportation (Caltrans) is based upon the following publications:
1. Traffic Manual (Caltrans)2. Standard Specifications (Caltrans)3. Standard Plans (Caltrans)4. Signal and Lighting Design Guide (Caltrans)
A minimum of two luminaires should be placed at each freeway exit ramp and one luminaire at each freeway entrance ramp. Typical locations are shown in Figures 9-25 and 9-26. Typical locations for luminaires at the intersections of freeway ramps and surface streets are shown in Figure 9-26.One or more additional luminaires may be installed when justified by geometrics, traffic patterns, background ambient lighting and/or freeway ramp traffic volumes. Additional lighting may be installed if ramp traffic meets the following volumes during one hour of darkness:
Where highway safety lighting is to be in-stalled at intersections on conventional highways,(including the intersection of a freeway ramp with a local street), the minimum maintained horizontal illuminance should be as follows:In urban areas and expressways, 1.6 horizontal lux on the area normally bounded by the crosswalks, and 6.5 horizontal lux at the intersection of centerlines of the entering streets.In rural areas, 1.1 horizontal lux on the area normally bounded by the crosswalks, and 3.2 horizontal lux at the intersection of centerlines of the entering streets.Electroliers at conventional highway intersections should be located as shown in Figures 9-27 and 9-28.To determine the position and number of luminaires needed to provide a desired lighting level or to determine the lighting level achieved by a given pattern of luminaires, the isolux diagram for the luminaire may be used. The lighting level at any point may be approximated by adding the values shown by the isolux curve passing through the point from each contributing luminaire.Isolux diagrams for the commonly used luminaires are shown in the Standard Plans. These diagrams represent the minimum acceptable values and therefore are appropriate for use with any particular manufacturerís luminaire. Transparancies of these diagrams in various scales are available to facilitate their use. Since these diagrams are based on initial values, a light depreciation factor must be applied to determine the maintained level of lighting.
Some overhead directional signs are illuminated. The sign lighting equipment and installation details are shown in the Standard Plans.
Tunnels should have sufficient illumination during the day so that vehicles inside the tunnel may be seen by approaching motorists. All interior walls and ceilings of tunnels to be lighted should bepainted or tiled in a light color. All concrete surfaces to be painted should have a Class 1 finish.Tunnels over 90 m long may require lighting in the daytime.Tunnels 30 m to 90 m long normally do not require daytime lighting but interior walls and ceiling should be painted. Conventional night lighting should be installed.
Lighting should be considered for all passageways including pedestrian openings through or under falsework. The faces of all falsework and forms located within or adjacent to the traveled way should be illuminated on the approach sides during the hours of darkness.
At locations in the interchange area where a special ramp for buses and a bus stop are provided, a minimum of one luminaire should be provided at the bus stop and at each crosswalk on the freeway ramp.
Lighting of Park-and-Ride Lots is desirable, not mandatory. There may be several legitimate reasons why lighting is not provided, e.g., in a rural area where line extension charges would be excessive. The following guidelines should be used in determining the amount of lighting to be installed where it has been determined that we can provide lighting without excessive cost:
1. Use lighting units on utility-owned poles whenever possible.
2. Design the lighting to provide 0.6 lux (minimum) in the darkest area of the facility.
3. Keep the number of poles and fixtures to the minimum necessary to meet the 0.6 lux level.
4. Design for all-night illumination.
Section 9-11 - Lighting Standards
Lighting standards for installation on State highways will normally be one of the types shown in the Standard Plans. The exception is where a local public agency uses different lighting standards and (a) has existing lighting that is being replaced due to State highway construction, or (b) desires the inclusion of their roadway lighting into a State highway project. (See Sections 9-09.2 and 9-09.5 for policy and financing.) Details for each type of lighting standard are shown in the Standard Plans.
Types 15 and 22 standards are used on conventional highways and expressways. Also, they may be used at the intersection of freeway ramps with surface streets. The Type 15 may be used on structures in lieu of a Type 21 standard where a lower mounting height is desired. The mast arm length normally used is 3.7 m, but lengths of 1.8 m, 2.4 m, 3.1 m and 4.6 m are available.The Type 21 standard is used on structures and may be mounted on the barrier railing, on the structure deck or on a retaining wall. The mast arm length normally used is 3.7 m. Lengths of 1.8 m, 2.4 m, 3.1 m, or 4.6 m are available.Types 30, 31, and 32 standards are used on freeways and in freeway interchange areas. The Type 30 is used where the standard cannot be located further than 5.5 m from the edge of the traveled way. Normal mast arm length is 4.6 m and lengths of 1.8 m, 2.4 m, 3.1 m and 3.7 m are available. The Type 31 is available only with a 6.1 m mast arm and should be located a minimum of 6 m from the edge of the traveled way. The Type 32 is available only with a 9.1 m mast arm and without a slip base, and should be located a minimum of 9 m from the edge of the traveled way.
Foundation details and foundation installation details for each lighting standard are shown in the Standard Plans.Location of foundations shall be as follows:
1. Lateral (Set Back).In general, lighting standards should normally be set as far from the right or left edge of the pavement as conditions permit. Exceptions to this occur in cut or fill sections with slopes steeper than 1:4; foundation locations for these conditions are shown in the Standard Plans. On curved ramps, lighting standards should be located on the inside of the curve.2. Longitudinal.a. Normal spacing for Types 21, 22, 30, 31 and 32 standards is 55 m. Normal spacing for Type 15 is 46 m.b. Typical locations for standards are shown in Figures 9-25 through 9-28.3. Structures.On structures and retaining walls, lighting standards should be located at least 1.5 m from the structure expansion joints or hinges. Care should be taken in locating electroliers on lower roadways or structures so as not to be a glare source to vehicles on a higher structure.
Slip bases shall be used under Types 30 and 31 standards and under Type 15 standards on freeways, expressways and conventional highways where speeds are in excess of 64 km/h. Exceptions to this policy are that slip bases are not used under lighting standards upon which signals are mounted or under lighting standards located:
a. On or behind structures, retaining walls or barrier railing;
b. In sidewalk areas;
c. Behind guardrail;
d. More than 9 m from traveled way; or
e. Where pedestrians would be close enough to be endangered by a pole knockdown.
Section 9-12 - Luminaires
Normally, the luminaire for a new installation of safety lighting on State highways is a full-cutoff type using a high pressure sodium lamp.
freeways, 200-watt lamps shall be used with 9.14 m mounting heights and
310-watt lamps shall be used with 12.19 m mounting heights. On conventional
highways and at the intersections of freeway ramps with surface streets,
150-watt lamps shall be used with 9.14 m mounting heights.
Utility owned semi-cutoff type luminaires should be provided with glare shields in rural areas.
Soffit luminaires are special fixtures either suspended from or flush-mounted into structures to illuminate the roadway under the structure. They shall be used with 70 or 100 watt high-pressure sodium lamps, depending upon lighting requirements. Normally, the fixtures should not be located over the traveled way on freeways.
Wall luminaires are fixtures designed to be surface mounted on vertical surfaces. However, a simple right angle bracket permits mounting them from a horizontal surface such as the bottom slab of a box girder. They are used with the same lamps as soffit luminaires.
Section 9-13 - Conduit, Wiring and Circuits
The design of a traffic signal or highway safety lighting system should provide adequate capacity, both in wire size and conduit size, for the proper operation of the complete system. In addition, it is important to include adequate capacity in the electrical system to allow maintenance to make repairs safely and promptly. One example of this is the spare conductors that are provided in major conduit runs for a traffic signal.
Installation of conduit shall conform to the requirements of the Standard Specifications.
The types of conduit most often used in traffic signal and highway safety lighting circuits are:
1. Rigid steel conduit.2. Rigid steel conduit that has been coated with polyvinyl chloride or polyethylene.3. Rigid nonmetallic conduit. Normally, this is Schedule 40 PVC conduit for underground installations and Schedule 80 PVC for above ground installations.4. Liquid tight flexible metal conduit.5. Intermediate steel conduit.6. Flexible nonmetallic conduit.
The minimum size of conduits for various applications should be as follows:
1. Traffic Signal installations:2. Highway Lighting:
a. Roadway Crossings 53Cb. Detector 41Cc. Signal Standard to Pull Box 53Cd. Controller Cabinetto Pull Box (2)78Ce. Service Cabinet to Pull Box 41Cf. Interconnect 41C
a. Pull Box to Pull Box 41Cb. Light Standard to Pull Box 41Cc. Soffit Light to Pull Box 35Cd. Service Cabinet to Pull Box 41C
The National Electrical Code limits the portion of the conduitís cross section that can be occupied by conductors to the following:
One Conductor 53%Two Conductors 31%Three or More Conductors 40%
However, for traffic signal installations, the conduit fill for new conduit should be limited to 26% and for existing conduit should be limited to 35%. This will compensate for the large number of conductors, the length of the run and the number of bends. Table 9-8 shows the cross-sectional areas of the conduits commonly used in traffic signal installations.
Conduits should be run either parallel to or at right angles to the structure girders. A variation of ±15 degrees is acceptable.Except for sidewalk joints, a conduit expansion fitting should be installed at each structure joint, hinge or abutment where a longitudinal movement of 12 mm or greater may occur. Where a lateral movement of 6 mm or greater may occur, an expansion-deflection fitting should be installed. Details for placement of expansion fittings and expansion-deflection fittings are shown in the Standard Plans.
Pull boxes should be installed to limit the length of conductor pull, to provide a point where conduits can be branched and/or conductors can be spliced and to simplify access to standards, poles and cabinets.
Pull Boxes should be installed:
1. At 60 m, or less, spacing in conduit runs;
2. At locations where conduits branch;
3. Adjacent to the foundation for each signal standard, lighting standard, illuminated sign, controller cabinet or service cabinet; and
4. At the toe of slope or at the hinge point when placed on a slope.
Pull boxes should not be installed in the traveled way if it can be avoided. When it is necessary to install them in the traveled way, the box, cover and foundation should be capable of supporting heavy wheel loading.
The minimum size of pull boxes for various applications should be as follows:
|1. Signal or Lighting Conduits||No. 5|
|2. Adjacent to Signal or Lighting Standards||No. 5|
|3. Adjacent to Controller Cabinet||No. 6|
|4. Adjacent to Service Cabinet||No. 5|
|5. Detector Termination||No. 5|
|6. With 4, or more, Conduits||No. 6|
|7. Telephone Conduits||No. 5|
Pull boxes with transformers should be provided with extensions.
The dimensions of conductors normally used in traffic signal and highway lighting circuits are shown in Table 9-9. The values shown in the table may be used to calculate conduit fill.
The conductors between the service point and the load (lamps, ballasts, controller cabinets, etc.) should be sized to limit the voltage drop to less than 5%.The resistance (ohms per 1,000 m) of conductors commonly used in traffic signal and highway lighting circuits is shown in Table 9-9. The values shown are based on an ambient temperature of 75o C.
Voltage drop can be calculated using:Volts Drop = 2ILRIf the voltage drop is known, the following formula can be used to determine the minimum conductor size:R = Volts Drop ÷ 2ILExample: The allowable voltage drop for a 380 m run feeding a 6.5 ampere load is 12 volts.R = 12 ÷ (2) (6.5) (.38) = 2.43From Table 9-9, the minimum wire size is No. 6.
Where: I = Current L= Length of Conductor (305 m) R= Resistance of Conductor
Traffic signal and flashing beacon control equipment normally is designed to operate on a 120-volt AC circuit.A 120-volt or 240-volt circuit is normally used for highway lighting circuits. For very large lighting circuits, a 480-volt circuit may be required.
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