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Section 2: Roadway Illumination Assemblies

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Item 610 - Roadway Illumination Assemblies

TxDOT standard pole lighting and underpass lighting is specified by Item 610, "Roadway Illumination Assemblies." Item 610 includes luminaires, poles, luminaire arms, anchor bolt assemblies, and conductors internal to the assembly. The poles must be fabricated at a plant on the MPL for Roadway Illumination Pole and Luminaire Arm Fabrication Plants.

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Lighting assemblies specified by Item 610 use three typical configurations based on the purpose of the lighting:

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  • Continuous lighting typically uses 50' light poles with either 400 watt HPS or the equivalent size LED. This configuration can light a roadway to minimal freeway levels up to 60' across the roadway from the luminaire.
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  • Safety lighting typically uses 40' light poles with either 250 watt HPS or the equivalent size LED. This configuration can light a roadway to minimal levels up to 50' across the roadway from the luminaire.
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  • Underpass lighting is typically mounted to the bridge structure at 16' mounting height, with either 150 watt HPS or the equivalent size LED.

TxDOT roadway illumination assemblies are designated by the RIP standards with the codes shown in Figure 5-1.

Explanation of roadway illumination assembly
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Figure 5-1. Explanation of roadway illumination assembly codes.

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DMS 11010

Item 610 of the Standard Specifications references DMS-11010, "Roadway Illumination Light Fixtures," as the main fixture specification. DMS-11010 in turn references DMS-11011 for LED luminaires, and DMS-11012 for HPS luminaires.

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RID Standards

The Roadway Illumination Details (RID) standards are used in most plan sets that contain illumination. RID(1) contains general notes needed for most installations. RID(2) shows details for illumination foundations. RID(3) has details for underpass illumination.

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LED Luminaires

TxDOT began using LEDs for roadway lighting in 2010. Before that, the dominant technology was high pressure sodium, which has been used since the 1970s. Since most of TxDOT's existing lighting infrastructure is based on HPS, the performance of TxDOT's LED luminaires is based on the equivalent HPS luminaires.

LED has several advantages over HPS for roadway lighting:

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  • HPS lamps have to be replaced every 3-5 years. LED luminaires do not have replaceable lamps, but are expected to last for 15-20 years. The long life reduces the need for maintenance, which saves time and money. Reduced maintenance also increases safety, since it requires less time for maintenance crews to work on the roadway.
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  • LED luminaires use less energy than their equivalent HPS luminaires. For example, at the time of writing, one of TxDOT's approved LED fixtures draws 185W compared to its 400W equivalent HPS fixture.
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  • LED luminaires emit white light, compared to the yellowish light of HPS. Colors are rendered better with white light and this can improve visibility for the driver.

TxDOT LED roadway luminaires are specified by DMS-11011. Features of the specification include:

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  • Three standard sizes of LED luminaire: 150W EQ, 250W EQ, and 400W EQ. The sizes correspond to the equivalent 150W, 250W, and 400W HPS standard luminaires used by TxDOT. The LED fixtures may be used as direct replacements for their equivalent size HPS luminaire.
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  • Unique Light Loss Factor (LLF) computed for each fixture at 70,000 hours (approximately 16 years). The design LLF is posted with each prequalified luminaire on the MPL.
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  • Verification testing of luminaires by the manufacturer. The luminaire manufacturer tests a sample of each batch of fixtures built, and sends the results to TRF for evaluation. If the sample meets specifications, TRF passes the batch and the fixtures are released for construction. Fixtures do not need to be sampled and tested from the project unless the engineer sees a need for it.
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  • Surge protection. Surge protection to 10kA and 10kV is included on the luminaire to help ensure long life.
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  • Warranty. The luminaires are warranted for 10 years when non-operable due to defects in the material or workmanship. A date code is included on an internal label to verify the warranty period.
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HPS Luminaires

TxDOT's HPS roadway luminaire specification is DMS-11012. The standard luminaire sizes are 150W, 250W, and 400W.

In most cases LED is a better choice for roadway lighting than HPS because of LED's maintenance and energy benefits. However HPS is a valid light source and may be used as long as it is available.

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TRF reviews LED luminaire submittals for conformance to DMS-11011, and reviews HPS for conformance to DMS-11012. When all testing and documentation has been received and accepted, the luminaires are added to the MPL for Roadway Illumination and Electrical Supplies. The six standard configurations are: 150W EQ, 250W EQ, and 400W EQ; with input voltages of either 240V or 480V.

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Light Loss Factor (LLF)

The LLF is a depreciation factor based on how the light output of a fixture decreases with time. All photometric calculations for illumination design should use the LLF that corresponds to the luminaire used.

For LED the LLF is based on how well the luminaire dissipates heat. An LED luminaire that dissipates heat well will depreciate slower, and will have a higher LLF than a luminaire that does not dissipate heat well. For TxDOT LEDs the LLF is between 0.70 and 0.90, and is posted with each luminaire on the MPL. The method for determining a LED luminaire's LLF is in DMS-11011.

For HPS, the LLF is based on the depreciation characteristics of a HPS lamp. TxDOT's design LLF for HPS is 0.65.

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Light Distribution Patterns

The Illumination Engineering Society (IES) writes many of the industry standard specifications for fixtures. The IES has designated several standard types based on their light distribution patterns. Figure 5-2 shows plan views of light distribution patterns for the basic types of conventional luminaires. TxDOT standard roadway luminaires are typically IES Type II or Type III.

Plan views of light distribution patterns
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Figure 5-2. Plan views of light distribution patterns for basic types of conventional luminaires.

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Luminaire Poles

Luminaire poles specified by Item 610 are made of galvanized steel or aluminum. The poles and arms must be fabricated at an approved plant in accordance with DMS-7380. The MPL for Roadway Illumination Pole and Luminaire Arm Fabrication plants contains a list of the plants that meet the specifications.

Poles fabricated according to the RIP standards at an approved plant do not require shop drawing submittals. Aluminum poles and alternate designs to the RIP standards require electronic shop drawing submittals.

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RIP Standards

The Roadway Illumination Pole (RIP) standard sheets contain the specifications and details for TxDOT's standard illumination poles. It includes details for shoe base poles, transformer base poles, barrier-mounted poles, luminaire arms, anchor bolts, and pole bases. The RIP sheets should be included in the plans whenever standard luminaire poles are used on a project.

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Shoe Base Poles

Shoe base poles have a square baseplate and are bolted directly to a foundation, bridge bracket, or retaining wall bracket. These poles will not break away when struck by a vehicle and should only be used in locations where they are not likely to be hit. Typical locations for shoe base poles are behind guard rails, outside the clear zone, or mounted on a bridge or retaining wall bracket.

Shoe base poles have a hand hole near the bottom of the pole for access to electrical connections. Even though the pole is not breakaway, the RID standards require a two-pole fused breakaway connector for the internal conductors that is accessible through the hand hole. This can be used to disconnect the luminaires from the circuit as needed during maintenance.

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Transformer Base Poles

Transformer base (T-base) poles are similar to shoe base poles, but the base plate is sized to fit on top of a transformer base, which is bolted to a foundation. T-base poles are designed to break away when hit, and should be used in locations inside the clear zone where they might be struck by a vehicle.

The transformer base originated in the days when the ballast (or transformer) for the luminaire was placed in the base of the pole, and the fixture housing and lamp were at the top of the pole. When luminaires began using internal ballasts, the T-base was kept for its breakaway characteristics even though it was no longer needed to house the ballast.

A transformer base is a breakaway support made of aluminum. TxDOT T-bases are designed to have the strength to support a 50 foot pole with two 12 foot arms, and also to be easily broken on impact (frangible). Transformer bases must meet AASHTO requirements and also must be impact tested and approved by the FHWA. TxDOT's approved T-bases are listed under Item 610 on the MPL for Roadway Illumination and Electrical Supplies.

Transformer base poles do not typically have a hand hole in the pole, but the electrical connections are made up in the T-base. TxDOT T-bases have a non-metallic door to discourage metal theft. The RID standards require a two-pole fused breakaway connector for the internal conductors to be placed in the T-base. If the pole is hit and breaks away, the breakaway connector will safely separate the pole from the electrical circuit.

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Light Pole Foundations

A roadway illumination foundation is necessary for all ground-mounted light poles. They are typically specified by 0416 6029 DRILL SHAFT (RDWY ILL POLE) (30 IN). The foundation's concrete and steel is included in Item 416, and the anchor bolts are included in Item 610. If a riprap pad is used around the foundation, it is typically specified by 0432 6001 RIPRAP (CONC)(4 IN).

Details for TxDOT's standard roadway illumination foundations are on the RID(2) standard sheet. The standard diameter is 30 inches, and the depth is 6 to 10 feet, depending on soil conditions. Roadway illumination foundations are measured by the linear foot of drill shaft depth.

In previous standards, grounding for the foundation consisted of a ground rod in the foundation plus a bonding conductor between the anchor bolts and the steel in the foundation. The bonded steel and anchor bolts create a concrete-encased grounding electrode (see NEC 250.52(A)(3)). A concrete encased grounding electrode typically has lower resistance and creates a better connection to ground than a ground rod. Since the concrete-encased electrode creates a good ground, the ground rod in the foundation was removed from the latest version of the standard.

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Poles on Traffic Barriers

Luminaire poles are frequently mounted on traffic barriers when barriers are available. Poles on barriers have good protection from being hit and are able to efficiently light traffic lanes in both directions.

Barrier-mounted poles have a special 8 in. x 18 in. rectangular base plate that will fit on the top of a traffic barrier. The round pole is "squashed" at the base by the fabricator so it will fit on the narrow base plate.

Barrier-mounted poles have hand holes for access to wiring, and all hand holes should be oriented on the same side of the barrier for easier maintenance. Even though the pole is not breakaway, the RID standards require a two-pole fused breakaway connector for the internal conductors that is accessible through the hand hole. This can be used to disconnect the luminaires from the circuit as needed during maintenance.

Traffic barriers require extra reinforcement to support light poles. Details for mounting light poles on F-shape barriers are in the standard sheet CSB(4). Details for light poles on single-slope barriers are on standard sheet SSCB(4).

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Poles on Bridges

Light poles on bridges are typically mounted on concrete brackets along the outside edges of the bridge behind the traffic rail. The BL standard sheet contains electrical and structural details for installing lighting on bridges. Light pole locations on bridges should be shown on the bridge plan sheets as well as on the lighting sheets to help ensure the brackets are constructed along with the bridge slab.

The BL standard recommends structural locations for poles placed on bridges. To reduce pole vibration, the pole should be placed within an eighth of a bridge span distance from the bent. The pole should also be placed at least 4 feet from the center of any bent and at least 3 feet from any deck drain. These factors should be considered along with illumination levels when laying out pole locations.

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Poles on Retaining Walls

Light poles may be mounted on retaining walls with a concrete bracket behind the traffic rail. The structural and electrical details are on standard sheet RW(LB). The pole should not be placed on the bracket until after the coping and pavement have been constructed.

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Breakaway Connectors

Breakaway connectors are fused or unfused connectors in the bases of light poles. Fuses are required in the "line" conductor (hot wire) of all light poles for circuit protection. This is accomplished by using special pull-apart fuse holders (breakaway connectors). If the light circuit uses a neutral conductor, the neutral part of the breakaway connector should be unfused.

TxDOT uses double-pole breakaway connectors that are designed to separate both power conductors at once. In addition to being a breakaway device, they also work well as a way to disconnect the luminaire from the rest of the circuit. For this reason, double-pole breakaway connectors are required in both breakaway and non-breakaway poles, to serve as a breakaway device and as a way to disconnect the luminaire.

When installing a breakaway connector, attach the female connector to the energized end of the wire. Leave the male connector with the wires traveling up the pole. This reduces the possibility of someone coming into contact with the energized circuit if the pole is knocked down.

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Underpass Lighting

Underpass lighting is mounted to the bridge structure and is detailed on RID(3). Luminaires are typically 150W EQ but may be larger for heights above 16'. Each lighting circuit on a bridge requires a lockable fused disconnect mounted at least 10 feet above grade on the bridge column or bent cap.

Type 1 underpass assemblies are mounted with 2 in. diameter arms on the bent cap of the bridge. This is the simplest mounting and may be used when the bent is close enough to the roadway for the underpass lighting to be effective.

Type 2 underpass assemblies are mounted on the bridge beams, and are used when lighting mounted on the bent would be too far from the edge of the roadway to be effective. Type 2 arms are attached near the top of the beam to avoid the beam's internal reinforcing steel strands. If the height of the beam is less than 54 in. then the luminaire is mounted on a 2 in. diameter arm. If the height of the beam is greater than 54 in. then the clamped part of the arm is 2 ½ in. diameter, and reduces down to 2 in. where the luminaire is attached.

Each underpass luminaire is protected with internal 10 amp time delay fuses to remove the luminaire from the circuit in case of failure. Underpass circuits that use a neutral require one fuse per fixture, and circuits with two hot conductors require two fuses per fixture.

Standard sheet RID(3) has details for Type 1 underpass, Type 2 underpass, and general notes applicable to most underpass installations.

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Item 616 - Performance Testing of Lighting Systems

Performance testing under Item 616 is included in the specifications for roadway illumination under Item 610 and high mast illumination under Item 614. Item 616 calls for a 14 day operational test, with 48 hours of constant operation followed by 12 days of operation controlled by photocell. Once the system passes the 14-day test and the contract is accepted, TxDOT will relieve the contractor of maintenance responsibilities.

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