Section 4: Conventional vs. High Mast LightingAnchor: #i1004424
Conventional lighting systems are lighting systems using mounting heights of 50 feet or less. High mast lighting uses mounting heights of 100 feet or more.
This section compares the advantages and disadvantages of conventional and high mast lighting and provides guidelines for deciding when to use high mast lighting.Anchor: #i1004441
Installation cost comparisons between high mast and conventional lighting systems vary widely, depending on the application. High mast lighting for interchanges is frequently less expensive to install than conventional lighting, due to reduced complexity of conduit and conductor and the smaller number of fixtures and poles required. Outside the interchange, conventional lighting usually requires a smaller initial cost.Anchor: #i1004451
Maintenance costs for the two types of systems differ greatly.
Conventional lighting requires the use of a bucket truck and frequently requires extensive traffic control, such as signs, cones, and lane closures. When poles are mounted on concrete traffic barriers, the inside lane usually has to be closed, resulting in significant traffic disruptions and safety hazards.
One or two persons with a pickup truck can usually perform maintenance on a high mast lighting system. High mast lighting may also eliminate the risks involved with having personnel working near high-speed traffic.Anchor: #i1004471
Some Deciding Considerations
Some important questions to consider when deciding whether to use conventional or high mast lighting are:
- Anchor: #YQYXNMEM
- Will lane closures be necessary for maintenance? What will be the effect on traffic? Anchor: #IXPLSHTM
- What is the initial cost difference? Anchor: #HMVHRQJY
- What is the maintenance cost difference? (When designing a lighting system, consider all maintenance costs, including costs incurred by other governmental bodies.) Anchor: #NGGESHJK
- Would future upgrading of the roadway require relocating a conventional lighting system? Can a high mast system be installed that will not require relocation and that can provide construction lighting for future roadway projects? Anchor: #QVLUTKYX
- What is the proximity of airports and residential areas?
High Mast Systems Recommended
High mast lighting should be considered for most urban interchanges that qualify for complete interchange lighting and for tangent sections of freeways with initial average daily traffic (ADT) of 70,000 or greater where lane closure would be necessary for the maintenance of a conventional lighting system and where a study shows that substantial traffic flow disruptions would occur during such lane closures.Anchor: #i1030592
FAA Obstruction Evaluation
If high mast poles are to be placed within approximately 4 miles of an airport, the Federal Aviation Administration (FAA) may require an Obstruction Evaluation / Airport Airspace Analysis (OE/AAA) to ensure air safety.
Notice must be filed with the FAA if requested by the FAA or when anyone proposes any of the following types of construction or alteration:
- Anchor: #OQVDLJRT
- any construction or alteration exceeding 200 feet above ground level Anchor: #EIUJINVC
- any construction or alteration that exceeds
an imaginary surface extending outward and upward at any of the
- Anchor: #VLBJIUEB
- 100 to 1 for a horizontal distance of 20,000 ft. from the nearest point of the nearest runway of each airport described in 14 CFR 77.9(d) with its longest runway more than 3,200 ft. in actual length, excluding heliports. Anchor: #KARTVWMF
- 50 to 1 for a horizontal distance of 10,000 ft. from the nearest point of the nearest runway of each airport described in 14 CFR 77.9(d) with its longest runway no more than 3,200 ft. in actual length, excluding heliports. Anchor: #YAQVFHYO
- 25 to 1 for a horizontal distance of 5,000 feet from the nearest landing and takeoff area of each heliport described in 14 CFR 77.9(d).
- any highway, railroad or other traverse way for mobile objects, of a height which, if adjusted upward, as defined in 14 CFR 77.9(c), would exceed a standard of 14 CFR 77.9 (a) or (b). Anchor: #RSUMWXJF
- any construction or alteration located on an airport described in 14 CFR 77.9(d).
The notice may be filed electronically online with the FAA on the FAA website.
The FAA may request additional information such as a survey signed and sealed by a Registered Professional Licensed Surveyor (RPLS) before making a final determination.Anchor: #i1034528
High Mast Systems and Light Trespass
High mast lighting should not be installed in areas where light trespass is an issue. This is generally areas where residential development is located directly along the highway right-of-way and pole placement is limited to the outside of the roadway. Special high mast designs should be considered to avoid light trespass, if high mast lighting must be employed. See "Glare and Sky Glow Issues" in the next section of this chapter for more information on light trespass.Anchor: #i1034599
High Mast Design and Layout
Layouts for high mast lighting are much more complicated than those for conventional lighting, since there are many different lighting fixtures and schemes available. The TxDOT Traffic Operations Division (TRF) provides high mast illumination design assistance upon request. High mast lighting design procedure is beyond the scope of this manual.
High mast lighting layouts should include soil boring logs. See the Geotechnical Manual (Bridge Collection) for details.