The impact of roadway lighting practices on the surrounding environment is of increasing concern to the public and DOTs, out of concern for impacts on wildlife as well as energy efficiency and cost. Light pollution is an unwanted consequence of outdoor lighting and includes such effects as skyglow, light trespass, and glare. " Sky glow" is a brightening of the night sky caused by natural and human-made factors. " Glare" is an objectionable brightness or reflection of light and a driving hazard especially bothersome for older drivers. "Light trespass" is the actual light that falls off the right-of-way and can be measured and quantified. In fact, many professional lighting designers have been obliged to go out at night and take measurements of the light that is falling off the right-of-way and onto a concerned citizen's property. Cities and states in some cases have responded with lighting ordinances and requirements regarding certain types of fixtures, minimum and maximum lighting levels, lumen/acre limits, and lighting elimination in some cases. Legislation has been adopted in Arizona, California, Connecticut, Colorado, Maine, New Mexico, Texas, Georgia, and New Jersey. Such legislation has been p roposed or introduced in New York, Iowa, Massachusetts, Michigan, New Hampshire, Maryland, Pennsylvania, Rhode Island, Virginia, and Wyoming. A number of North American transportation jurisdictions have initiated the process of re-evaluating all aspects of roadway lighting systems to respond to the increasing public demands to provide safe, efficient and cost-effective systems. The benefits of adopting new design methods and technologies such as small target visibility (STV) method for design, counter-beam technologies in tunnels and new techniques for dynamic management of roadway lighting systems are widely recognized by North American transportation and illuminating engineering communities.

 

In the last two decades, research into lighting concepts, along with major advancements in computer simulation and design software, has led to the development of new techniques and methodologies for the design of efficient, effective, safe and environmentally responsive roadway lighting systems. These advancements were acknowledged in the millennium edition of the Lighting Handbook of the Illuminating Engineering Society of North America (IESNA). [N] In addition, the United States Federal Highway Administration has completed a study on lighting design concepts and the American Association of State Highway and Transportation Officials is currently updating its Informational Guide for Roadway Lighting. The AASHTO guide provides guidelines for when lighting should be installed, traffic volumes, and other criteria for locating lighting. IESNA has also recently approved a revision to its American National Standard Practice for Roadway Lighting (RP8). The National Standard primarily deals with appropriate levels of lighting for different installations.[N][N][N] The revision includes three methods for designing continuous lighting systems for roadways: illuminance, luminance and small target visibility (STV). Advanced technologies in lighting hardware have been applied in most of the industrialized countries of Europe. [N][N] Some DOTs have updated their own manuals based on these new standards and resources. For example, Oregon DOT produced a Traffic Lighting Design Manual in January 2003, which drew on RP8 and implemented some lighting reductions, including a study on whether light removal would be possible.

In August 2005, the Transportation Association of Canada expects to complete a Roadway Lighting Guide. The guide will incorporate two decades of research into lighting concepts combined with major advancements in computer simulation and design software have resulted in new techniques and methodologies for design of efficient, effective, safe and environmentally responsive roadway lighting systems. Advanced through the Traffic Operations and Management Standing Committee (TOMSC) of the Transportation Association of Canada, the guide completely revises the TAC's 1983 Guide for the Design of Roadway Lighting, a national guide providing a general outline of engineering practices, warrants, planning methods, design techniques and the design criteria for roadway lighting systems. The project has utilized the expertise and experience from a variety of international sources in formulating the contents of the new Guide for the Design of Roadway Lighting. The final approved draft of the TAC's guide to Illumination of Isolated Rural Intersections is also due in 2005.

 

High pressure sodium (HPS) lights are the most commonly used type of roadway lighting in the U.S. They have the inherent advantages of long life, and hence less maintenance, low cost, energy efficiency and good long range optical control. Low pressure sodium (LPS) and metal halide (MH) are also used to provide roadway lighting. All of these sources are energy efficient. Newer sources such as inductive fluorescent, compact fluorescent and light emitting diodes may be practical sources in the future.

There are many valid reasons where lighting is not only needed, but required. It is important to understand the lighting objectives and how much is enough, in order to balance the need for lighting while minimizing light pollution and increasing energy efficiency. A number of social and economic benefits are attributable to roadway lighting, including but are not limited to:

• Facilitation of traffic flow,
• Reduction of nighttime accidents,
• Aid to police protection,
• Promotion of roadside businesses, and
• Safety for pedestrians and bicyclists.

Initial practices in assessing lighting needs include:

• Identification of community objectives and whether the street in question needs lighting.
• Identification whether other ways exist to accomplish the goals without installing lighting (including marking, mechanical structures, etc.)

Once lighting is deemed necessary, the following inquiry is recommended practice:

• Are minimum lighting levels being used to accomplish the objectives?
• Is the current or proposed lighting installation energy efficient?
• Are all attempts being made to minimize light pollution? One of the most common recommended practices in terms of minimizing light trespass has been use of full cut-off fixtures. A "full cutoff luminaire" is one that allows no direct light emissions above a horizontal plane through the luminaire's lowest light-emitting part.
• Have maintenance and component life been considered? Have easy mechanisms for opening, removing lamps and ballasts, and cleaning been considered? Will special tools or equipment be needed?
• Is the lighting installation cost effective?
• Have lighting controls such as motion sensors or timers been considered?
• Is a lighting curfew (turning lights off after a certain time) appropriate?
• Are pole heights and pole spacings appropriate? Use an appropriate light for the location. In different locations, different pole heights are appropriate.
• The "cobra head" type of luminaire seen on many streets and roadways is often found on a higher pole, spreads light further, and is often not fully shielded
• Architectural or decorative types of luminaires might have a scale that requires shorter pole heights.
• When existing utility poles are used, careful attention to luminaire selection is important so that it is suitable for the pole heights
• The height of street lighting poles will impact how uniform the light levels are in the street and surrounding area. This issue can be especially important in a retrofit installation where existing pole mounting locations are going to be used with no additional poles.
• Almost all lamps used in street lighting require a ballast to provide the proper voltage and current to the lamp. Are efficient ballasts going to be used? Even the most efficient lamp and ballast can be made very inefficient by using luminaires that trap light inside. A luminaire that emits less than half of the light generated by the lamp and ballast should be avoided.

Further recommendations by biologists investigating the impacts of lights on wildlife include the following: [N][N]

• Lighting should be restricted where protection of biodiversity is a high priority, such as in unusual ecological habitats, and in certain agricultural and horticultural settings.
• To limit artificial lighting, light sources should be turned off whenever illumination is not essential.
• Lamp housings should be sealed tight, and located away from structures that may trap insects.
• Low-pressure sodium lamps should be used in preference to other kinds of lamps.

Arizona DOT Research to Improve Lighting Practices

ADOT has undertaken research on whether it is possible and desirable to improve lighting design practices, with particular attention to observers greater response to the yellow light portion of the spectrum. Nighttime visibility has been shown to be influenced by the lamp type used for roadway lighting, because the lamp's spectral output can influence sensors in the retina that are active at night. ADOT undertook a research project to determine the status of the subject and to find what can be done or needs to be done to better define the issues of useful lighting and to assess potential benefits. Both IESNA and CIE have established committees to review available knowledge of the subject and develop related technical publications. [N]

ADOT outlined the following questions with regard to current roadway lighting practice:

• Do different lamp color (or spectral power distribution) characteristics affect visibility and safety in a real roadway environment in a way that has a meaningful or measurable effect on driver performance?
• If a different choice in light source spectral distribution from that most commonly used now does result in potential driver performance improvement, what would be the tangible benefits be: reductions in crashes, light pollution, energy use?
• What would the drawbacks be: increased light pollution, more maintenance, higher initial costs?
• Certain local regulations require the use of a specific lamp type, which has raised controversy. Can ADOT conform to regulations requiring the use of a particular lamp type while meeting desired goals?
• Can and should ADOT make a change from its current designs to light sources with different color rendering characteristics, such as metal halide, or low pressure sodium?
• Can and should ADOT recommend changes to standards writing bodies from their current design standards to lower lighting levels, or to higher lighting levels?
• What maintenance issues are involved in changing lamp type?
• Does the current state of research justify an immediate change to lighting design practice or is more research needed to see if the current results are in fact meaningful?

Comparison of Lighting Sources, Issues, and Costs

The Arizona DOT developed a side-by-side comparison for the three sources for the lighting of a major roadway, using identical design specifications or each of the three. Each design was optimized for maximum pole spacing. The results by lamp type and pole spacing were:

• 400 watt High Pressure Sodium (HPS) 276 ft.
• 180 watt Low Pressure Sodium (LPS) 176 ft.
• 400 watt Metal Halide (MH) 246 ft.

Primarily as a result of these pole spacings, HPS provided the lowest initial system cost. MH had a 7 percent higher initial cost than HPS, while LPS was 41 percent more expensive than HPS. Power costs for HPS and MH were essentially identical, but were 24 percent lower for LPS. Considering overall operating costs, including maintenance, MH was 7 percent more expensive than HPS, while LPS was 12 percent less expensive. These values were based on a cost of 8 cents per kilowatt hour. Life cycle costs, based on a 30 year life, were 7 percent higher for MH versus HPS, and were 17 percent higher for LPS versus HPS. [N]

Florida DOT also investigated (LPS) lighting, as an alternative to (HPS), which is the most widely used type of lamp for street lighting. However, other drawbacks were noted by FDOT: [N]

• The large fixtures required for LPS typically did not meet Florida wind loading criteria, and the fixtures deteriorated relatively quickly in the salt-air environment of coastal roadways resulting in higher maintenance;
• Both initial and operational costs for LPS lights are substantially higher than for HPS lights;
• The distribution of lighting is more difficult to control (more lights are needed for uniform distribution);
• Replacement cycles for LPS lights are more frequent than for HPS lights (i.e., shorter operational life); and
• LPS have environmental concerns that require special disposal procedures.

While initial costs for LPS lights are higher than for HPS lights, electricity costs are generally lower, because LPS lamps are more efficient (more lumens per watt). In practice, operational costs may vary, depending on how the lights are used in a particular utility's lighting system. Regardless of overall costs, there are some drawbacks to LPS usage. Principal among those are the large fixtures required to house the lamps. These fixtures are susceptible to damage during high winds, require more maintenance, and typically have more omni-directional broadcast properties than conventional light fixtures (i.e. more difficult to control light distribution).

Florida DOT's Coastal Roadway Lighting Manual

Florida DOT has undertaken lighting research primarily because the state's beaches serve as important nesting habitat for several species of threatened and endangered sea turtles. Artificial light on or near nesting beaches can negatively affect the nesting process by interfering with normal nocturnal behaviors and spatial orientation of sea turtles, a problem to which streetlights contribute. Consequently, FDOT contributed to development of a Coastal Roadway Lighting Manual. Guidelines and alternative lighting recommendations contained in the manual were the collaborative effort of a Technical Working Group of lighting experts, traffic engineers, public safety personnel, utility customer service managers, biologists, and regulatory agency personnel. The partners had found that the previous lack of basic guidelines for streetlight management often resulted in duplication of effort, inadequate resolution of identified problems, delays in implementation of effective solutions, and/or unnecessary expense and an adversarial climate between those requiring that lighting be modified and those responsible for affecting a solution. The intent of streetlight management was to 1) confine light to the area of its intended use; 2) reduce the amount of light emitted to the minimum required to effectively achieve its intended purpose, and/or, 3) use light sources that minimize the potential for wildlife and hatchling disorientation.

When a lighting system is incorporated into a roadway improvement project, the FDOT Project Design Engineer refers to the Plans Preparation Manual for information on how to justify and design the system to applicable safety standards. Design elements include distance between poles, pole height, light source, wattage, illuminance, and clear zone requirements. The proximity of proposed lighting systems to environmentally sensitive areas is not always considered. However, the Project Design Engineer can request a design exception if variances from minimum safety standards are needed to reduce the potential for lighting impacts. This requires coordination with the Federal Highway Administration. To better address wildlife needs, FDOT lighting specialists now draw from the following list of options to reduce roadway lighting impacts in the following section.

Lighting Environmental Stewardship Practices

Best practices to reduce glare and improve visibility included: [N]

• If using cobrahead fixtures, use a flat-glass cobrahead instead of the typical horizontally mounted high-output lamp in the cobrahead-style fixtures, where the glass refractor lens on the lamp-head creates direct glare that is accentuated during extreme weather conditions such as rain, sleet, snow, and fog. This fixture still has bright spots under the pole that create glare, but is a better alternative.
• Install lights at uniform heights, which helps the eye avoid having to adjust to extreme ratios of alternating higher and lower lights.
• Avoid use of "offset fixtures," mounted at an angle, with much of the resulting light wasted, going into the sky where it can affect nearby residential neighborhoods as well as the flight patterns of migratory birds. Some studies suggest that street and roadway lighting cause as much as 50 percent of the skyglow in our major urban areas. Many cities have already adopted ordinances against light trespass and light pollution from homes and businesses.
• Utilize full cutoff fixtures to direct light and reduce light trespass.
• Ensure lighting is energy efficient.
• Install improved reflector systems and vertical lamps to put light more accurately in areas where light is desired. Vertically lamped fixtures can be mounted in a median and serviced from one side. Usually, one fixture can replace two or more cobrahead fixtures used in traditional designs. With an optimized fixture design, one can lower mounting heights and still meet required lighting levels. This type of installation usually has a lower first cost and, because it mandates fewer poles and fixtures, a much lower maintenance cost. Energy consumption is usually lower.
• Avoid overlighting. Utilize the IES Standard Practice (RP-8) manual on Roadway Lighting, adopted as the American National Standard Practice in 2000.
• Realign the fixture (change angle of mounting arm or rotate fixture head) so the source of light is not directly visible outside the ROW.
• Apply a shield to a drop globe fixture.
• Change an open bottom or drop globe fixture to a cutoff fixture.
• Apply a shield to a cutoff fixture.
• Reduce the mounting height of the fixture.
• Reduce the lamp wattage.
• Change the lamp socket position in the fixture to compress the lighting footprint.
• Change to a fixture with a different type of reflector providing a more favorable lighting footprint.
• In addition to other shielding and light reduction measures: Install a flat 2422 acrylic amber lens in a cutoff fixture with an HPS lamp of 70 watts or less (e.g., GELS 70W M250).
• Turn the light off.
• Remove the fixture.
• Relocate the fixture to block light from extending to sensitive resources.
• Change to an LPS fixture (if the light is customer-owned).
• Create a vegetated berm/buffer or other light shield between the roadway and the sensitive resource.

Electric utilities can generally provide the following options:

• Seasonally turn the lights off.
• Relocate or redirect the light fixture.
• Change a drop globe fixture to a cutoff style fixture.
• Remove the fixture.
• Lower mounting height.
• Reduce wattage.
• Selectively install amber-colored filtering lenses (on cutoff fixtures of 70-watts or less and only in addition to other modifications).
• Install a light shield.

An overview of roadway lighting fixtures is available at the MetroLux Lighting website. [N]

FDOT's Embedded Roadway Lighting Study

In order to further study alternative roadway lighting systems, FDOT funded a demonstration project in 2001 that utilized embedded roadway lighting products. Consultants contracted by FDOT researched available lighting products, designed and installed a system, and are currently maintaining it. A roadway section was selected because there was a history of hatchling disorientations on adjacent beaches, there was a vegetative screen between the road and the beach, the roadway is not heavily traveled in the summer months, and the community was particularly sensitive to the needs of sea turtles. The purpose of the project was to determine if innovative lighting techniques could illuminate pavement markings without impacting sea turtles on adjacent beaches. The modification involved deactivating the existing overhead street lighting, placing amber lenses on existing pedestrian pathway lights, and installing low bollard mounted luminaires along the pedestrian and bicycle ways. As a safety countermeasure, an embedded pavement lighting system was installed in the roadway. In general, area lighting levels and uniformity were reduced by the elimination of the overhead lighting. The remaining pedestrian area lights provided adequate illumination levels along the pedestrian pathway. Visibility in the travel lanes and in the bicycle lanes appeared to have been adequate for the traffic conditions of the roadway. The embedded roadway lighting and the low bollard luminaires served principally as delineation aids. [N]

Caltrans Light Minimization Efforts

In response to the energy crisis in California, Caltrans voluntarily adopted requirements for lighting controls by zones, maximum lighting power, and shielding of luminaires. Luminaires were required to be off during the day and all luminaires greater than 100 watts to be IESNA cutoff type or full cutoff. [N] Caltrans is exploring designs that yield peak candlepower in the range of 65°to 72° yield, as those are the most economical roadway/outdoor layout. Avoidance of light above 80° from vertical was also recommended, as such light never reaches the ground, causes direct glare, and generates the most number of complaints. [N]

Tennessee DOT Light Reduction and Maintenance Cost Savings

Tennessee DOT recently took a closer look at lighting opportunities and tradeoffs and found opportunities for significant payoff. A value engineering proposal for a new intersection designed with off-set style cobrahead lighting mounted in the right-of-way outside the safety shoulders was revised to use a vertically mounted lamp in an optimal, architecturally designed roadway fixture directed from a 40-ft. pole placed on the median barrier. True cut-off fixtures were installed, eliminating light trespass and light pollution; power consumption stayed the same in terms of first-cost dollars and cents. The change provided the state with several important benefits: [N]

• Skyglow and light trespass were greatly reduced. People in surrounding residential neighborhoods were pleased with the reduction in stray light and fewer impacts to the natural environment were likely.
• Lighting levels on the roadway were increased, creating a safer highway and a safer intersection.
• Fewer fixtures and poles were required, reducing anticipated maintenance costs.
• Savings included more than 5 miles of trenching and backfilling and more than 5 miles of cable that no longer needed to be provided.
• Sixty-one pole foundations, poles, and fixtures were eliminated. The new median lighting system involved installation of 26 poles and fixtures mounted on median barrier walls.
• Considering maintenance, the cost of the lighting project was considerably reduced.

Tennessee DOT implemented alternatives to traditional roadway lighting practices that created visibility, maintenance, and safety problems, as well as escalating installation costs. [N] TDOT used many of the best practices listed in the earlier section on roadway lighting fixture options.