The Future of Roadway Lighting: Researchers Studying the Role of Illumination in Traffic Safety Make
[ILLUSTRATION OMITTED] Roadway lighting offers significant safety benefits but alsorepresents a substantial share of the operating budgets of agenciestasked with maintaining the lighting infrastructure. Standard practicerequires that roadway lighting systems, when installed, provideillumination for the maximum vehicle and pedestrian volume, regardlessof roadway conditions or real-time roadway usage. Typical practice alsorequires maintaining a single, specific lighting level over time, whichis difficult to do, because as a light source is used, it diminishes inoutput due to aging of the source and dirt that accumulates on the lens.To overcome the expected reduction in output, engineers tend toovercompensate in the initial lighting design by specifying the use ofmore intense luminaires to reach the correct lighting level. These traditional approaches to lighting design result insignificant over-lighting of roadways and excessive energy usage.Adaptive lighting, that is, adjusting illumination levels based on theneeds of roadway users, offers an approach to overcome these challenges. Driven by the development of new lighting technologies and anationwide push to reduce energy use and environmental impacts, adaptivelighting is a growing trend in the roadway industry. It entails the useof a design methodology in which the light output of a system adjusts astraffic conditions change. More specifically, the level of lighting canbe reduced or dimmed when traffic on highways or sidewalks lessens.Here's a look at how adaptive lighting may be implemented whilemaintaining the safety of road users and how two agencies are deployingthis technology on their roadways. Implementing Adaptive Lighting Although transportation agencies have begun to introduce adaptivelighting into their roadway projects, the techniques for doing so haveyet to be standardized. In 2011, the Federal HighwayAdministration's Office of Safety Research and Development launchedthe Strategic Initiative for the Evaluation of Reduced Lighting onRoadways to investigate the issues associated with the application ofadaptive lighting to the roadway environment and to develop recommendedpractices for implementing those systems. In July 2014, the FHWA Office of Safety Research and Developmentreleased a report titled Design Criteria for Adaptive Roadway Lighting(FHWA-HRT-14-051). This report describes an indepth effort to assess theeffect of adaptive lighting on the overall safety performance ofroadways. Researchers working with FHWA conducted studies to determineoptimal times, conditions, and suitable approaches for reducinglighting; appropriate lighting levels for various roads and features;energy savings and reductions in greenhouse gases resulting from reducedlighting; and potential legal issues. The resulting design methodology provides a process thattransportation agencies can use to determine whether adaptive lightingis appropriate for a given roadway. The researchers proposed a set ofcriteria to assist jurisdictions in making sound, safety-based decisionswhen considering adaptive lighting approaches. In addition, thestudy's evaluation of real-world lighting data can serve as thefoundation for future analyses related to roadway lighting. Roadway Light, Visibility, and Safety For part of the research resulting in the 2014 report, the FHWAOffice of Safety Research and Development partnered with the VirginiaTech Transportation Institute to investigate how lighting levels affectsafety on the road, and to develop an approach for selecting appropriatelighting levels for various roads and features. Previous research hadshown that roadway lighting can affect crash risk. For this study, theresearchers analyzed the relationship between lighting levels andquality and crash rates. Establishing such a relationship can helpagencies determine the optimal lighting level for roadways under varioustraffic conditions. Four criteria to consider in the design of roadway lighting arehorizontal and vertical illuminance, luminance, and uniformity.Horizontal roadway illuminance is the amount of light falling on theroadway surface. Vertical illuminance is the amount of light falling ona vertical surface, such as a pedestrian. Luminance is the amount oflight perceived by the road user, and uniformity is the ratio ofilluminance or luminance values, such as maximum to average, average tominimum, or maximum to minimum. Researchers used detectors mounted on top of a vehicle to collectdata to measure each of these criteria on thousands of miles of roadwayin seven States (California, Delaware, Minnesota, North Carolina,Vermont, Virginia, and Washington). After taking measurements, theresearchers compared the varying lighting levels, roadwaycharacteristics, and traffic volumes with night-to-day crash rate ratioson segments of road. This ratio reflects the relative magnitude ofnighttime crash risk compared with daytime crash risk. Because daytime and nighttime crashes shared the same road designfeatures and traffic control features, the crash rate ratio directlyreflects the factors that only differ by day and night, with visibilitylevel being the primary one. Therefore, the night-to-day crash rateratio indicates the effect of lighting and light levels whilecontrolling for the effects of roadway design, traffic control features,and other roadway characteristics. The researchers considered thenight-to-day crash rate ratio to be the primary metric in evaluating theeffect of roadway lighting on safety. (Note that weather conditions werenot included in this analysis and therefore represent a basis for futureresearch.) The researchers analyzed more than 88,000 crashes that had occurredfrom 2004 to 2010. Of those, more than 64,000 crashes had occurredduring the day, while nearly 24,000 had occurred at night. The NationalOceanic and Atmospheric Administration's recorded sunrise andsunset times were used to classify the natural lighting into daytime andnighttime conditions. [ILLUSTRATION OMITTED] Horizontal Illuminance Next, the researchers analyzed roadway horizontal illuminance, orthe amount of light falling on the roadway surface, as one of fourroadway lighting criteria in the study. They calculated the relationshipbetween the horizontal illuminance of roadway segments and thenight-to-day crash rate ratio of those segments. The results of their analysis show a significant decrease in thenight-to-day crash rate ratio with an increase of average horizontallighting levels, which are measured in foot-candles, or lux. In thestudy, the night-to-day crash rate ratios for lighting levels 0 and 0.1foot-candle (0 and 1 lux) are significantly higher than for otherlevels. However, there is no statistically significant difference forlighting levels from 0.19 to 0.65 foot-candle (2 to 7 lux), and anincrease in the lighting level from 0.46 foot-candle (5 lux) to higherlevels did not appear to affect the crash rate ratio. There appears tobe a further reduction in the crash rate at approximately 1.49foot-candles (16 lux); however, because data on only 28 miles (45kilometers) of roadway are represented in this category, the result isnot statistically significant. These findings indicate that althoughlighting will benefit road safety, increasing the lighting level doesnot necessarily always lead to a safer road. [ILLUSTRATION OMITTED] Maintaining Roadway Safety With Less Light After conducting similar analyses for each of the other lightingmetrics, the researchers concluded that the possibility exists forreducing standard lighting levels on roadways during periods of lesstraffic while maintaining the overall level of roadway safety. In one case, the data revealed the potential for reducing standardlighting levels on urban interstates by as much as 50 percent. Theresearchers calculated the minimum illuminance requirement for variousroad classifications and compared those requirements with roadwaylighting guidelines issued by the Illuminating Engineering Society ofNorth America (IES). The research team calculated that the lightinglevel required for urban interstates is 0.37 foot-candle (4 lux), whichis significantly less than the 0.84 foot-candle (9 lux) that IESrecommends. The results for other roadway classifications show that theexisting IES recommendations are suitable; the researchers'calculations resulted in lighting levels that fall within the range ofIES minimum and maximum standards. Selecting Lighting Levels Selecting the appropriate lighting level for various roads andfeatures is a critical aspect of adapting the lighting system. TheInternational Commission on Illumination, a lighting standardsorganization, devised a system that provides both a methodology forselecting the lighting design level and a method for adapting thelighting level based on specified criteria for individual roadways. FHWAand the Virginia Tech Transportation Institute researchers based theirdesign methodology on this system to comply with the internationalstandard, but the team also proposes a more extensive classificationsystem to take advantage of the benefits of adaptive lighting forroadways. Additional metrics include links to IES requirements andconsideration of traffic volume, geometric design, and pedestrianvolume. The proposed system starts with the IES characterization of thefacility to be lighted. The IES separates lighting design criteria byits application to roadways, streets, and residential or pedestrianfacilities. First, roadway lighting criteria are provided for freeways,expressways, limited access roadways, and roads on which pedestrians,cyclists, and parked vehicles are generally not present. Second, streetlighting criteria are provided for major, collector, and local roadswhere pedestrians and cyclists are generally present. Criteria forresidential/pedestrian area lighting are provided primarily for thesafety and security of pedestrians and not specifically for drivers.Once a lighting designer selects the facility type, he or she uses thecharacteristics of the facility as weighting functions to determine therequirements of the lighting system. The designer then subtracts the sum of these weighting values froma base value. The base value changes based on the facility type. Forroadways, the base value is 5. When the sum of the weighting values issubtracted from the base value, the result is called an"H-class." If the result of this calculation is not a wholenumber, the next lower positive whole number is used (for example, H3-5would use the H3 lighting level class). Negative numbers would result inapplying the highest lighting level, or HI class. Similarly, if thecalculated number is higher than the highest class number, the lowestlighting level, or H4 class, is used. Once the lighting designer calculates the H-class, he or shedetermines the design criteria for the roadway. For each class, thelighting levels are specified in terms of average luminance, uniformity,and veiling luminance. The average luminance is the average lightinglevel on the roadway. The uniformity represents the ratio of the averageto minimum light level and the average to maximum light level. Theseuniformity ratios control the range of light and dark on the roadway.The veiling luminance is a measure of glare and limits the amount oflight that is projected by a luminaire towards a driver. For an adaptive lighting system in which the lighting level changesbased on the conditions of the roadway, the weighting functions changeas the roadway conditions change. This determines a different lightingclass and therefore a different required design level. Timing Lighting Adjustments Some conditions that can change throughout the night and influencethe lighting level required to maintain safety include traffic volume,pedestrian and bicycle presence, parked vehicles, ambient conditions,and pedestrian safety and security. As these conditions change, anadaptive lighting system will adjust luminance levels accordingly.(Weather conditions, such as fog, rain, and snow, are also factors thatinfluence lighting level, but they were not included in this analysis.) Two approaches typically used to trigger lighting adjustments in anadaptive system include curfews, in which the lighting system changes ata predetermined time, and roadway monitoring. Curfews are used to adaptlighting systems during defined time periods. Operators establish curfewtimes based on an evaluation of parameters of interest. For example,operators could evaluate average traffic and pedestrian volumes on anhourly basis to determine the timing of adaptive changes. Operators needto be able to override the adaptive cycle, as needed, for specialevents. Actively monitoring the roadway through pedestrian and vehiclecounts is an alternative to curfews. Active monitoring requires vehicledetectors or the review of roadway video to determine when to adjustlighting levels. The resource requirements for a monitoring system canbe significant, although they might become less demanding once connectedvehicle and connected infrastructure technologies provide a new sourceof data on traffic and pedestrian volumes. Controlling Lighting Adjustments The recommended technological approach to adaptive lighting isdimming. In the past, reduced lighting on roadways was typicallyaccomplished through switching or "half-code" lighting, inwhich every other luminaire or the luminaires on one side of the roadwayare turned off or removed. Although this method is cost effective,conserves energy, and is relatively easy to implement, half-codelighting makes it impossible to meet design criteria for uniformity andglare control. This approach presents legal issues because the inabilityto meet design criteria might affect the safety of roadway users. In contrast, dimming a luminaire facilitates adjusting the lightlevel without upsetting the other design criteria. Dimming luminairesare typically capable of dimming from 100-percent output to 10 percentof maximum output, depending on the technology of the light source.Although this method does not conserve as much energy aslight-extinguishing methods, its ability to maintain lightinguniformity' might be the best solution for conserving energy whileminimizing the likelihood of negatively affecting driver or pedestriansafety. Light-dimming methods have other advantages. Dimming lights insteadof leaving them fully on at night reduces the effect of sky glow (a formof light pollution) and reduces disruptions to organisms' circadianrhythms--the physical, mental, and behavioral changes that follow aroughly 24-hour cycle, responding primarily to light and darkness in theenvironment. Disruptions to circadian rhythms can impact sleepingpatterns and general health and well-being. Dimming works particularly well with solid-state lighting, whichuses semiconductor LEDs as a source of illumination rather than electricarc lighting and, by its nature, dims more smoothly. In addition,solid-state lighting conserves energy, typically yielding a 50-percentreduction in energy use over traditional lighting. Using an adaptivelighting design with solid-state luminaires can further reduce energyusage. Converting to solid-state luminaires also might reducemaintenance costs because they last longer than traditional lightsources. Legal Implications of Adaptive Lighting The parties most concerned with the legal implications of anadaptive lighting system are the owners of such systems and theirdesigners. The owner will likely be the government agency responsiblefor drafting the regulations defining the system and for implementingit. The designers include the engineers and design professionals workingfor the owner or agency. The legal concerns involved range from the agency'sjustification for implementing such a system to the legal liability ofthe owners and designers in the event of a personal injury lawsuitattributed to the adaptive lighting system. For the agency implementing an adaptive lighting system,demonstrating the basis for the application of its expert discretion iscrucial when defending its decision to implement the system. Supportingthe decision with empirical data will strengthen the case for needingthe system, as will adherence to industry-accepted guidelines in thesystem's design. A narrative explanation of the agency'sreasons for the decision to implement the system--written or endorsed bythe engineers with the particular expertise--will leave little doubt asto the basis for the new system. A well-supported agency decision willlikely receive substantial deference from a reviewing court. Adaptive Lighting Systems in Use Today San Jose, CA, has implemented a widespread adaptive lightingsystem. Since 2008, the city of San Jose has gradually upgraded its62,000 yellow sodium vapor streetlights to use LEDs and paired them witha remote monitoring and adaptive control system. This approach enablesthe city to boost the efficiency and life expectancy of itsstreetlights, obtain timely and accurate information on the performanceof its lights, and modulate lighting levels to provide only the amountof light needed. The control system for the streetlight network provides real-timereporting of energy usage and non-operating streetlights for improvedresponse. Converting to LED lighting reduced streetlight energy costs by40 percent to 60 percent, while improving lighting quality andvisibility and enhancing safety. The city is earning ongoing savings byextending the maintenance cycle for bulb replacement, and it receivescredit from Pacific Gas and Electric (PG&E) for dimming itsstreetlights in the late evening hours. "In 2011, San Jose supported the California Street LightAssociation in negotiations with PG&E for a pilot program to reducethe energy bill for controllable luminaires for a few streetlightcustomers," says Gregory Jobe, an associate engineer who works forthe city. "By late 2015, we will have implemented anetwork-controlled dimmable streetlight pilot program open to allPG&E's streetlight customers at a reduced administrative cost.After an introductory period of a few months, the dimming schedule maybe adjusted on an annual basis, and the tariff may be evaluated forpotential modifications." By switching to more energy-efficient lights and modulating itslighting levels in relation to changing activity levels, San Jose willsave 1,885,000 kilowatt-hours annually, avoiding emissions equivalent toapproximately 1,433 tons (1,300 metric tonnes) of carbon dioxide. Thatsavings is equivalent to the volume of greenhouse gases emitted annuallyby 274 passenger vehicles. San Jose aims to replace 100 percent of the city'sstreetlights with LED lighting equipped with an adaptive control systemby 2022. The city expects to convert more than 20,000 lights by the endof 2015. So far, the city has concentrated on heavily used majorroadways and a contiguous area in the southeastern portion of San Jose,including lights on a number of corridors identified as having a highpercentage of pedestrian and bicyclist injuries and fatalities. Otherpriority locations include 20 areas identified by the local policedepartment as gang activity hot spots, as well as areas with a high rateof streetlight wire theft. The streetlight control system providesreal-time notification of circuit malfunctions, enabling the city tointervene and deter wire theft. "Overall, residents have reported that they feel safer afterdark because they can see better," says Amy Olay, planning andsustainability division manager with San Jose. "Others areimpressed by the LEDs' lighting quality, although we have receivedsome complaints. One complaint is that the lights are too bright,shining into houses. In those cases, we adjusted the tilt of the LEDfixture to correct the problem." Adaptive Lighting In Cambridge, MA The city of Cambridge, MA, is replacing about 7,000 lights (4,900streetlights and 2,100 in specialty and park fixtures) with LEDs andinstalling an adaptive control system that enables fine-tuning of lightoutput, reduction of energy use, and energy usage tracking capabilities. The city developed a system of classification to determineappropriate lighting levels for each street. Using detailed informationfrom the city's geographic information systems database, as well asonsite evaluations, staff assessed streets for width, light polespacing, and vehicular and pedestrian activity, and assigned each tocategories corresponding to lighting criteria in accordance withindustry guidelines, including the IES Standard Practice for RoadwayLighting (RP-8-14) and Technical Memorandum on Light Trespass (TM-11). After comprehensive analysis, the city assigned the streets to arange of categories that address lighting requirements for both roadwaysand sidewalks, and limit glare and light trespass onto abuttingproperties. A wireless control system enables operators to dim thestreetlights to 70 percent of their initial brightness. Later in theevening, the lights dim even further to about 35 percent of theirinitial brightness in response to low pedestrian volumes at that time ofnight. The new streetlight system consumes less than 25 percent of theenergy of the existing streetlights, saving the city an estimated$500,000 per year in electricity costs. "Cambridge's initial reasons for using adaptive controlswere energy savings and asset management," says Glenn Heinmiller, adesign consultant involved in the project. "But we soon realizedthat significantly reducing light trespass by dimming later in theevening was a huge benefit, especially in our dense residentialneighborhoods." The new streetlights distribute light in a pattern similar to theold streetlights, but the amount of light crossing property lines fromthe public way will typically be half as much as with the existinglights, and even lower late at night. The new streetlights make colorslook brighter and more faithful to the natural color. Trees look greeninstead of brown, a blue car looks blue instead of grey. Because of thisimproved color rendering, everything appears brighter and sharper underthe new streetlights, even when the amount of light is less than withthe old lights. Lowered light levels are sometimes perceived as unsafe to roadwayusers and pedestrians, but residents in Cambridge have not raisedconcerns about the new lighting. "Based on our experience inCambridge," Heinmiller says, "I think that fears that loweredlight levels will be perceived as unsafe are unfounded. In our city of100,000 residents, we've had no comments about lower levels. No onehas complained or even seemed to notice when the light levels are cut inhalf." The Future of Adaptive Lighting Systems Adaptive lighting systems effectively reduce the cost and extent ofthe undesirable effects of roadway lighting while maintaining safety andusability. Integrating these systems with tools that are capable ofsensing and communicating near real-time electrical and lighting datafrom the field will make it possible to control lighting levels moreeffectively--and even on demand. Vehicle-to-infrastructure communicationsystems that send real-time information to operating systems couldcontrol lighting in response to just a single vehicle. [ILLUSTRATION OMITTED] The Virginia Tech Transportation Institute has createddemonstration prototypes of an on-demand lighting system. On-demandlighting systems also could help first responders by flashing lightwhere assistance is needed or along evacuation routes during disasters.Although these technologies are still in the early stages ofdevelopment, adaptive systems are already shining light on today'sincreasingly dynamic roadway environment. Ronald B. Gibbons, Ph.D., is director of the Center forInfrastructure-Based Safety Systems and is the lead lighting researchscientist at the Virginia Tech Transportation Institute. He also is thedirector of Division 4 of the International Commission on Illuminationand a past president of the IES. Gibbons earned his Ph.D. in systemsdesign engineering from the University of Waterloo, Canada. Joseph Cheung is a civil engineer in the FHWA Office of Safety,where he helps develop safety technologies. He has B.S. and M.S. degreesin civil engineering, with an emphasis on traffic and transportation,from the University of Maryland. Cheung is a registered professionalengineer in Maryland. Paul Lutkevich, P.E., has more than 30 years of experience in thedesign and research of exterior lighting systems. He is the past chairof the IES Roadway Lighting committee and Technical Review Council. Healso is a member of the International Commission on Illumination.Lutkevich has a B.S. degree in electrical engineering from theUniversity of Massachusetts Dartmouth. For more information, see www.fhwa.dot.gov/publications/research/safety/14051/14051.pdf or contact Ron Gibbons at 540-231-1581or , Joe Cheung at 202-366-6994 or, or Paul Lutkevich at 617-960-4903 or.