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Section 6: Conducting Studies

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Before developing a master lighting plan, a study should be conducted by traffic and lighting engineers familiar with lighting design standards, warrants for lighting, sky glow and light trespass issues, lighting system maintenance, electrical systems, traffic crash studies, and lighting controls. The study is needed for the following reasons:

  • to determine how the various lighting systems can best be optimized and coordinated
  • to justify the implementation of lighting curfews
  • to justify expenditures for technological improvements such as ELMS.

This section describes the recommended scope of such a study. Generally, the study should cover:

  • the electrical system
  • the purpose of the lighting system
  • benefits and effects of curfews and dimming
  • traffic studies
  • surrounding land use and surrounding lighting
  • security concerns
  • sky glow and light trespass issues
  • community goals
  • coordination with navigation authorities
  • traffic management interaction
  • controls
  • curfew monitoring
  • ELMS Implementation
  • coordination with roadway maintenance and construction activities
  • budget.

Discussions of each of these items follow under separate subheadings.

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Electrical System

The study should evaluate electrical energy use and the potential for savings. This should include an assessment of the age, leakage current, and overall condition of the system.

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Purpose of Lighting System

Determine the purpose of the lighting system. If the lighting was installed to improve safety because of high traffic volumes, it might be reduced to complete interchange lighting or partial interchange lighting after normal traffic volumes subside. Likewise, if safety during periods of high pedestrian traffic is the primary purpose of the lighting, it could be reduced or turned off after the pedestrian traffic subsides or is not expected.

Continuous roadway lighting is not expected to eliminate nighttime crashes nor can curfews be blamed for causing crashes. The precise effect of lighting roadways is not known. Continuous lighting has generally been shown to lower crash rates from 20 to 60 percent. Consider partial interchange lighting, which provides lighting only at decision making locations such as intersections and ramp gores where most crashes occur. Remember, the only required nighttime lighting is that of automobile headlamps.

The best use of resources may be to use fixed lighting on busy roadways and facilities during the time of their peak usage. This could free up funds now spent on lighting roadways in the early morning hours so they can be spent on lighting more roadways at peak traffic hours. In this way overall safety within the community is improved.

Determine how curfews would affect the historical, civic pride, and other extenuating circumstances relate to the lighting system.

Non-Roadway Lighting. Determine the purpose (need or enjoyment) and hours of use for non-roadway lighting systems for facilities such as:

  • parks
  • parking facilities
  • landscapes
  • historical sites
  • aesthetic structure lighting
  • hike and bike trails, etc.
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Benefits and Effects of Curfews and Dimming

Determine the benefits and effects of curfews and dimming.

Dimming should be considered if light levels are higher than those required by AASHTO. In some instances lighting is installed at levels higher than the minimum required because of safety or work zones. It may be reasonable to dim this to only the required level after heavy traffic subsides. The same logic can be applied to dimming as is applied to curfews.

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Traffic Studies

Assess the hourly nighttime traffic volumes and crashes.

Consider reducing continuous lighting to partial interchange lighting at the point during the nighttime hours when fatal crashes or severe injury crashes, analyzed over a three year period, is found to drop to half of the peak rate. Consideration may be given to the type of crashes and a study to determine if lighting is a factor in the specific traffic safety problem.

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Surrounding Land Use and Surrounding Lighting

Assess the surrounding land use and surrounding lighting. Consider other area lighting that exists outside the control of the master lighting plan. Check the laws or ordinances governing surrounding lighting. Curfews for occupancy or use for parks, downtown areas, or other areas may already exist.

High levels of surrounding lighting may dictate that roadway lighting not be reduced depending on:

  • proximity of such lighting to the roadway
  • light levels
  • glare and veiling luminance evaluations.

Normally roadway lighting should not be reduced to average light levels below that recommended by AASHTO when state or city owned lighting is provided on roadside sidewalks that is not also dimmed or turned off.

Determine the level of cooperation with private facilities that can be achieved.

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Security Concerns

Assess security and vandalism concerns. Motion detectors used with incandescent or fluorescent lighting may be considered for use in non-roadway applications. Light levels and light source color may be a consideration for areas under video cameral surveillance.

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Sky Glow and Light Trespass

Check for local light trespass and sky glow laws, restrictions, and ordinances.

Assess the system’s sky glow and light trespass contributions. Determine community desires for sky glow and light trespass reduction (see Chapter 6, Conventional vs. High Mast Lighting. )

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Community Goals

Conduct a survey of community goals for lighting.

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Coordination with Navigation Authorities

Coordinate with air and sea navigation authorities when applicable. For example, lighting or lighted facilities may be used in some areas as landmarks for pilots.

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Traffic Management Interaction

Determine the anticipated level of traffic management staffing. Dimming and curfew schemes can be better implemented if personnel are available to intercede with timely action such as turning lighting on at crash locations and programming for special events. This may require that traffic management centers be manned at all hours of the night.

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Consider various algorithms or methods for control, including:

  • control of selected areas, such as parks, central business district (CBD), residential streets, commercial streets, highways, freeways, parking lots, and rest areas
  • on and off times
  • the extent of the reduction of the lighting (reducing or extinguishing the lighting on interchange ramps, gores, and intersections is not recommended)
  • degree of control (time clocks or modern electronic controls)
  • modification of curfew schedules due to weather and special events.
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Curfew Monitoring

Consider methods, need, and ability to monitor implemented curfews. Long-range monitoring of algorithms will help ensure optimum performance.

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ELMS Implementation

Determine how and when the electrical and lighting management system (ELMS) may be implemented. See Electrical and Lighting Management Systems, Section 5 of this chapter for information on ELMS.

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Coordination with Roadway Maintenance and Construction Activities

Consider how dimming and curfew schedules should be adjusted to accommodate nighttime maintenance and construction operations so that motorists are alerted to unusual planned activities.

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Consider how the master lighting plan relates to the following budgetary factors:

  • how the plan would affect the budget for lighting installation and maintenance
  • how the plan would affect the budget and methods for other traffic safety devices
  • what the budget would be for installing controls.
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