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Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations
|This report is an archived publication and may contain dated technical, contact, and link information|
|Publication Number: FHWA-HRT-14-050 Date: June 2014|
Publication Number: FHWA-HRT-14-050
Date: June 2014
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The Federal Highway Administration’s Office of Safety Research and Development serves the highway safety community by conducting research that advances safety goals while accommodating practical considerations. The development of methodologies and tools that result from this research can assist practitioners who are looking to make safety-based decisions in the real world. The guidelines presented in this report address the need to maintain the safety effects of roadway lighting while alleviating the budgetary strains associated with the maintenance of the lighting infrastructure.
This report establishes a new set of criteria for practitioners to apply to their roadway environment that will identify appropriate lighting levels for given roadway characteristics and usage. Specifically, these guidelines identify the appropriate applications of adaptive lighting on roadways while maintaining the optimal level of safety. The methodology for applying the criteria is based on existing international standards that accommodate different roadway characteristics and usage. Therefore, practitioners will be familiar with the application of the results but will benefit from an enhanced data collection and statistical approaches when considering adaptive lighting applications.
The adaptive lighting criteria identified in this report are the first to utilize real-world lighting data collection and robust statistical analysis of crash histories of the associated roadways. Ultimately, these Guidelines will provide practitioners with the evidence-based criteria they need to determine the appropriate application of adaptive lighting systems in their jurisdictions. This allows for the unique opportunity to provide significant cost savings while maintaining the optimal level of safety for roadway users.
Monique R. Evans
Director, Office of Safety
Research and Development
This document is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The U.S. Government assumes no liability for the use of the information contained in this document. This report does not constitute a standard, specification, or regulation.
The U.S. Government does not endorse products or manufacturers. Trademarks or manufacturers’ names appear in this report only because they are considered essential to the objective of the document.
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1. Report No.
2. Government Accession No.
3. Recipient's Catalog No.
4. Title and Subtitle
Guidelines for the Implementation of Reduced Lighting on Roadways
5. Report Date
6. Performing Organization Code:
Ronald Gibbons, Feng Guo, Alejandra Medina, Travis Terry, Jianhe Du, Paul Lutkevich, David Corkum, and Peter Vetere
8. Performing Organization Report No.
9. Performing Organization Name and Address
Virginia Tech Transportation Institute
10. Work Unit No.
11. Contract or Grant No.
12. Sponsoring Agency Name and Address
Office of Safety
13. Type of Report and Period Covered
14. Sponsoring Agency Code
15. Supplementary Notes
This report provides guidelines for the implementation of an adaptive lighting system for roadway lighting. Based on the analysis of crashes and lighting performance, a series of criteria and the associated design levels have been developed to provide an approach for light level selection and the adjustability of the light level based on the needs of the driving environment. The application, the technology needs, the benefit cost, and the legal implications of adaptive lighting are also considered in this guideline document.
17. Key Words
Street Lighting, Adaptive Lighting, Energy Savings, Reduced Light Levels
18. Distribution Statement
No restrictions. This document is available through the National Technical Information Service; Springfield, VA 22161.
19. Security Classif. (of this report)
20. Security Classif. (of this page)
21. No. of Pages
|Form DOT F 1700.7 (8-72)||Reproduction of completed page authorized|
|Figure 1||Illustration. General structure of a lighting control system|
|Figure 2||Photo. Roadway lighting|
|Figure 3||Photo. Street lighting|
|Figure 4||Photo. Residential/pedestrian area lighting|
|Figure 5||Equation. Lighting class|
|Figure 6||Photo. Facial recognition under low lighting|
|Figure 7||Photo. Facial recognition under high lighting|
|Figure 8||Graph. Example system costs by year for standard and adaptive lighting systems|
|Figure 9||Equation. Present value|
|Figure 10||Graph. Example NPV for standard and adaptive lighting systems|
|Table 1||Street lighting levels from IESNA RP-8|
|Table 2||IESNA RP-8 street lighting levels for high-volume pedestrian areas|
|Table 3||IESNA RP-8 street lighting levels for medium-pedestrian areas|
|Table 4||IESNA RP-8 street lighting levels for low-pedestrian areas|
|Table 5||Assumptions made for the LOS calculation|
|Table 6||Threshold traffic volume based on LOS|
|Table 7||Hourly traffic flow criteria for roadways|
|Table 8||Hourly traffic flow criteria for streets|
|Table 9||Hourly traffic flow criteria for residential/pedestrian roads|
|Table 10||Â Roadway design level selection criteria|
|Table 11||H-class lighting design levels|
|Table 12||Street design level selection criteria|
|Table 13||S-class lighting design levels|
|Table 14||Residential/pedestrian design level selection criteria|
|Table 15||P-class lighting design levels (E = illuminance)|
|Table 16||Example lighting level selection process for a roadway facility|
|Table 17||Example lighting level selection process for a street facility|
|Table 18||Example cost information for an adaptive lighting system|
|Table 19||Cash flow comparison for an adaptive lighting system|
|AASHTO||American Association of State Highway and Transportation Officials|
|ADT||average daily traffic|
|CIE||Commission Internationale de L’Eclairage (International Commission on Illumination)|
|FAA||Federal Aviation Administration|
|FTCA||Federal Tort Claims Act|
|IESNA||Illuminating Engineering Society of North America|
|ILE||Institute of Lighting Engineers|
|ITS||intelligent transportation system|
|LOS||level of service|
|mcd/m2 lx||millicandela/meter squared lux|
|NPV||net present value|
|RP-8||Recommended Practice for Roadway Lighting|
|TAC||Transportation Association of Canada|
|vph||vehicles per h|
The impact of road lighting has been well documented, and its implementation is overwhelmingly regarded as positive; both drivers and pedestrians recognize the safety of being able to detect potential hazards at night. During the energy crisis in the 1970s, which affected metropolitan and rural areas, the removal of roadway lighting was hotly debated. Several studies conducted during this time assessed the impact of the presence or absence of roadway lighting. Other studies anticipated the installation of lighting along highways and evaluated the before-and-after effects of the lights. The results of these studies were not surprising: the presence of roadway lighting makes roads generally safer, while the removal of lighting decreases safety.
However, energy concerns continue to loom today, and the expenses associated with roadway lighting are typically a significant component of a transportation agency budget. New lighting and control technologies provide the ability to adapt the output of lighting systems based on road-user needs. Adaptive lighting allows lighting to be turned off or reduced when few or no vehicles or pedestrians are using the roadway; lighting can then be turned on or increased when needed. This process allows a reduction in the amount of energy consumed by lighting while maintaining the current level of safety that lighting provides to roadway users.
Current guidelines for roadway lighting already allow some adaptability. The Illuminating Engineering Society of North America (IESNA) Recommended Practice for Roadway Lighting (RP-8) defines the lighting level in terms of roadway type and potential for pedestrian interaction. (1) The Commission Internationale de L'Eclairage (CIE) provides a roadway lighting selection guide based on the characteristics of the roadway.(2) These two guidelines have been reviewed and are incorporated into the requirements defined as part of this document.
These Guidelines for the Implementation of Reduced Lighting on Roadways provide a process by which an agency or a lighting designer can select the required lighting level for a road or street and implement adaptive lighting for a lighting installation or lighting retrofit. This document supplements existing lighting guidelines. It is expected that the reader has knowledge of lighting design and the issues associated with the implementation of roadway lighting.
The objective of adaptive lighting is to use lighting only when it is required and at the appropriate level to provide for the safety of roadway users. Streets and roads are often overlighted, meaning that more light is used than the road users require. The reasons are threefold:
The philosophy behind adaptive lighting is to provide lighting only when and where it is needed, essentially managing the roadway lighting level as an asset. The light level on a roadway can be managed and controlled in two ways.
The first approach is to reduce the light output from the luminaire to the level required by the lighting design. This approach, typically referred to as "right sizing," avoids the output quantization problem by selecting a light source of appropriate size for the application. It is noteworthy that a right-sizing application typically includes a light level monitoring system to provide feedback for the control of the luminaire. This approach mitigates some of the maintenance issues by monitoring the light output over time and responding to deprecations in luminaire performance from dirt or lamp depreciation.
The second method is to adjust the light level based on current road conditions, which may include use of criteria such as traffic volume, vehicle mix, pedestrian activity, and weather. This document provides guidance on how to implement an adaptive lighting design, because it is more responsive to roadway user needs and provides greater efficiencies for the system owner/ operator.
The obvious and primary benefit of adaptive lighting is the reduction of energy use, which has been shown to be between 20 and 40 percent with adaptive lighting.(3) The other potential benefits of adaptive lighting are reductions in the following:
For an adaptive lighting solution to produce a financial benefit, the lighting system must have the following components:
The control systems are the primary component of the adaptive lighting methodology and are generally monitored and managed from a central location. A general outline of a lighting control system is shown in figure 1. Here, each individual luminaire is controlled from a central hub. Generally, each luminaire has an addressable control module that turns the luminaire on and off and manages any dimming requirements. This module communicates to a node controller that may manage as many as 2,000 or more luminaires. The node controllers then communicate with a central management system. The method of communication can be wired, via a power line carrier, or wireless. Wireless communication is a popular method, particularly for retrofits, because it does not rely on a formal network but can be created using self-healing mesh network techniques. Other sensors, such as weather detectors and ambient light monitors, may also be linked into the system to provide additional data for lighting management. This approach to lighting management falls under the general description of Electrical and Lighting Management Systems, and the National Transportation Communications for Intelligent Transportation System Protocol 1213 has been developed to provide commonality among the control systems.(4) It is also important to note that these systems may be part of the intelligent transportation system (ITS) of an agency and may need to comply with Federal requirements found in 23 Code of Federal Regulations 940.
Figure 1. Illustration. General structure of a lighting control system.
The second aspect of the adaptive system is the luminaire itself. The luminaire must be able to respond to the output of the control system and provide dimming. Dimming is the recommended method for adaptive lighting. In the past, reduced lighting on roadways has been accomplished through switching or "half-code" lighting, in which every other luminaire or the luminaires on one side of the roadway are turned off or removed. It is not possible to meet all of the existing design criteria for uniformity and glare control using half-code lighting scenarios. By contrast, dimming a luminaire allows the light level to be adjusted without upsetting the other design criteria. Dimming luminaires are typically capable of dimming from 100-percent output to anywhere between 50 and 10 percent of maximum output, depending on the light source technology. A controls-ready luminaire is one that is typically equipped with a driver that can be dimmed through a standard controller connection. The typical dimming control for a luminaire is a 0-10-volt control input that adjusts the light output based on the input voltage. Recently developed technologies can provide dimming and luminaire control to the individual luminaire via a module attached through the photo-control receptacle on the luminaire.
The final component of the adaptive system involves negotiation with the electrical utility. Most lighting systems are either owned by the electrical utility or are charged at a flat rate to the roadway agency when connected to an unmetered source such as the utility secondary feeders. To reap the financial benefits of an adaptive lighting system, the roadway agency must negotiate with the utility for a reduced rate or a rate based on metering of the electrical usage by the lighting system. Some control systems provide utility-grade metering that can be used for this purpose. However, it is vital that this aspect of the adaptive lighting system be negotiated before the system is implemented.
Several methods of classifying roadways and recommended lighting performance are available throughout the world. In addition to the IESNA, examples include the Transportation Association of Canada (TAC), the Institute of Lighting Engineers (ILE) in the United Kingdom, and the CIE.
The typical method for selecting a lighting level has been to first choose the road classification and then the potential for conflict. The IESNA RP-8 provides tables for this methodology of light-level selection; TAC has a similar system and levels. However, the applicability of this method to adaptive lighting on high-speed roads is limited, because the criteria that establish the potential for conflict do not change with time of day.
For street lighting, however, IESNA RP-8 uses peak hour pedestrian counts as the criterion for potential conflict. A volume greater than 100 pedestrians is classified as high, a volume between 10 and 100 pedestrians is classified as medium, and a volume of 10 or fewer pedestrians is classified as low. Table 1 shows IESNA RP-8 recommended lighting values for various street classifications based on these pedestrian volumes.
Table 1. Street lighting levels from IESNA RP-8.
|Road and Area Classification||Average
The recommended light level for a collector road with high pedestrian volumes is 0.8 cd/m2. If pedestrian volumes fall into a lower category during certain times at night, the overall classification of the street can change. Assuming the pedestrian volumes declined to less than 10 pedestrians per h, the lighting level on the roadway could be reduced to 0.4 cd/m2 using the existing IES RP-8 recommendations.
The lighting values in the American Association of State Highway and Transportation Officials (AASHTO) Roadway Lighting Design Guide are essentially the same as those in IESNA RP-8.(5) Instead of using pedestrian volumes as a subcategory for selecting a light level, the AASHTO guide uses the land use groups of commercial, intermediate, and residential. These land use categories were substituted for the pedestrian volume values of IESNA RP-8, but the values were all derived from the same initial recommended values. Changing the land use category used in the AASHTO guide would be the same as changing the expected pedestrian volume used in IESNA RP-8. Because the land use category does not change with time of day, it is difficult to use the AASHTO guide as a basis for adaptive lighting recommendations.
IESNA RP-8 also includes a pedestrian-volume-based criterion for the sidewalk areas adjacent to the roadways. Table 2 through table 4 show the lighting levels for streets with high, medium, and low pedestrian usage.
Table 2. IESNA RP-8 street lighting levels for high-volume pedestrian areas.
|Maintained Illuminance Values for Walkways|
|Mixed Vehicle and Pedestrian||20.0/2.0||10.0/1.0||4.0|
Table 3. IESNA RP-8 street lighting levels for medium-pedestrian areas.
|Maintained Illuminance Values for Walkways|
Table 4. IESNA RP-8 street lighting levels for low-pedestrian areas.
|Maintained Illuminance Values for Walkways|
(2 or fewer dwelling units per acre)
(2.1 to 6.0 dwelling units per acre)
Adaptive lighting techniques can also be applied to these recommendations, reducing both the horizontal and vertical illuminance values for the sidewalk based on expected pedestrian volumes. This method of determining lighting levels to be applied in adaptive technology is somewhat useful, but it is limited by its simplistic classification of roadways and street types.