Chapter 6: Lighting Design and Layout

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Section 1: Overview

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Project Design Procedures

Highway illumination project designers generally follow the steps shown in the table below.

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Determine whether the lighting will be safety lighting or continuous lighting; then check to see to what extent lighting is warranted. (See Chapter 2.)

If the project is inside a city’s limits, contact the city to see if they are willing to help finance continuous lighting for the project. (See Chapter 4.) Obtain the proper lighting agreement.

Determine what type of lighting to use (pole height, median or house side mounting or high mast). (See guidelines and standards throughout this chapter.)

Place lighting poles for the entire project. (See “Spacing of Light Poles” and “Pole Placement Guidelines” in this chapter.)

Contact utility company to determine the type of service available and possible electrical service locations. (See Chapter 7 “Electrical Service.”)

Lay out circuits, keeping road crossings to a minimum, as jacking or boring escalates costs. (See Chapter 7, “Circuit Design.”)

Determine and label poles, length and size of wire, conduit, and duct cable.

NOTE: Show pole station number and offset from base line or edge line if applicable.

For poles with similar offsets, offset can be shown by plan note.

Electrical service numbers and light pole numbers are recommended.

Prepare sheet summaries and project summaries. (The project summary shows the items and quantities needed for the entire project. It is compiled from the sheet summaries and usually includes the electrical service data.)

If the project is inside a city limit, submit plans and title sheet with the proper quotation for city approval and signature. (For example, see Chapter 4, “Quotation on Plan Title Sheet.”)

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Project Lead Time

For projects involving mainly illumination, an appropriate lead time must be allowed for the contractor to obtain the necessary materials. Typical lead time is 90 days for conventional lighting and 120 days for high mast lighting. This gives the pole manufacturers ample time to fabricate poles.

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Joint Usage

Joint usage of poles is encouraged to reduce roadside clutter and the number of fixed objects along the roadside. When lighting is provided at signalized intersections and when conditions permit, the luminaires should be mounted on the traffic signal pole.

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Luminaires on Traffic Signal Poles

Luminaires on traffic signal poles should be powered from the same electrical service that powers the traffic signal.

Luminaire arms should be perpendicular to the roadway to be lighted. TxDOT roadway luminaires are designed to project light to the left and right of the luminaire to efficiently light the roadway.

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Railroad Crossings

For work involving railroad overpasses, consult the Rail-Highway Operations Manual for required agreements with or notification of railroad companies.

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Underpass lighting may improve safety in situations where:

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  • the roadway beneath the underpass has continuous lighting on both sides of the underpass
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  • pedestrian activity is expected along the roadway near or beneath the underpass
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  • the geometry of the roadway changes beneath the underpass, for example a narrow shoulder
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  • other hazards exist.

If none of these situations exist, adding underpass lighting will not usually significantly improve the safety of the roadway.

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For lighting purposes, a tunnel is defined as a structure over a roadway which restricts the normal daytime illumination of a roadway section such that the driver's visibility is substantially diminished. Tunnels cover roadways and produce a shadow that limits the ability of the driver to see objects or obstructions within the tunnel.

Tunnel lighting can require both daytime and nighttime lighting. Tunnel lighting design is outside the scope of this manual. For more information, see the AASHTO Roadway Lighting Design Guide and ANSI/IES RP-22-11 Tunnel Lighting.

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Sidewalks and Bikeways

When installing lighting using state funds on sidewalks and bikeways (henceforth termed pedestrian lighting) along streets and highways, it is essential that the street be lit to the same level as the sidewalk or bikeway. This road lighting may be existing or may be added with the pedestrian lighting; it may be a part of the same lighting system or a separate lighting system.

This requirement is not intended to oblige cities or other entities to light the entire roadway if they desire some type of lighting along the roadway in accordance with Chapter 2, "Systems Financed, Installed, and Operated by Other Agencies." However, the following points are generally accepted and should be considered.

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  • The reduction of veiling glare is beneficial.
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  • Veiling glare observed by a motorist is mitigated by increasing the illuminance of the roadway.

The street and sidewalk or bikeway may be considered together as one element in determining minimum light level and uniformity. The contribution of both the pedestrian lighting system and the road lighting system may be considered for calculating light levels and uniformity of the sidewalk or bikeway and the roadway.

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Aesthetic Lighting

TxDOT uses aesthetic lighting to highlight roadway structures, walls, and landscaping. Further information and guidelines for aesthetic lighting are detailed in the Landscape and Aesthetics Design Manual, Chapter 4, Section 9.

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Other Types of Lighting

Other types of lighting systems (such as for rest areas, parking lots, central business districts, or temporary lighting in work zones) may be designed to meet the applicable requirements of AASHTO, IESNA, CIE, or other standards as deemed appropriate by the district engineer.

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