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Countermeasures for Mitigating Headlamp Glare . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21-2 Nighttime Driving . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21-4 Daytime Lighting Requirements for Tunnel Entrance Lighting . . . . . . . . . . . . . . . . . . . . . . .21-6 Countermeasures for Improving Pedestrian Conspicuity at Crosswalks . . . . . . . . . . . . . . . .21-8 Characteristics of Lighting that Enhance Pedestrian Visibility . . . . . . . . . . . . . . . . . . . . . . .21-10 Characteristics of Effective Lighting at Intersections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21-12 21-1 C H A P T E R 21 Lighting
COUNTERMEASURES FOR MITIGATING HEADLAMP GLARE Introduction Countermeasures for mitigating headlamp glare refers to road design elements that are effective for reducing the discomforting and disabling effects on visibility of exposure to glare from oncoming headlamps. The combination of high-intensity headlamps and high mounting heights in the vehicle fleet can result in greater exposure to glare for motorists. Several treatments are available for designing roadways that can reduce driversâ exposure to glare. Design Guidelines The following table presents advantages and disadvantages of various treatments for mitigating glare. Treatment Advantages Disadvantages Wide medians ⢠Greater glare angle reduces the glare effect ⢠Increased object contrast due to reduced background luminance ⢠Increased cost of construction, extra right-of- way purchase, median landscaping, and maintenance ⢠Increased time to cross an intersection may lead to less efficient traffic signal operation Independent alignments ⢠Can completely eliminate view of oncoming vehicle and associated glare ⢠Less earthwork required on slopes and other topographies, allowing flexibility in design ⢠More environmentally friendly ⢠Longer construction time compared to narrow median designs ⢠Larger right-of-way requirement Glare screens ⢠Effectively reduces glare ⢠Installation can be limited to specific problem areas ⢠Simple to install and maintain ⢠Reasonable cost ⢠Requires some type of barrier on which to install the screen ⢠Effective only when the vehicles are on the same level plane ⢠Do not work well with significant vertical curves Fixed roadway lighting ⢠Improved visibility of objects and pedestrians ⢠Increased adaptation level reduces glare effect ⢠High cost (installation, operation, and maintenance) ⢠Potential for crashes with lighting pole (mitigated with break-away mountings & greater setback) The Commission Internationale de lâEclairage (CIE) veiling luminance model below shows that veiling luminance increases as glare angle decreases. Wide medians reduce veiling luminance by increasing (1). Where: Iglare = luminous intensity of glare source = glare angle A = driver age Based Primarily on Expert Judgment Based Equally on Expert Judgment and Empirical Data Based Primarily on Empirical Data HFG LIGHTING Version 2.0 21-2
Di scu ssi on Glare occurs when the intensity of a light source within the visual field is substantially greater than the visual adaptation level, causing physical discomfort or pain (dis comfort glare) and/or reduced visibility (disability glare). A portion of th e light entering the eye is scattered in the transparent media of the eye (i.e., cornea, lens, and vitreous fluids) and by the tissues in the ocular fundus ( 2, 3 ). Some light also diffuses through the sclera and iris tissues. The scattered light superim poses a uniform veiling lu mi nance onto the retinal image, reducing its overall contrast. If the contrast of an object falls below the contrast threshold under these conditions, it will be rendered invisible. Furtherm ore, transient adaptation caused by rapid changes in lu mi nances within the visual field can cause further temporary reductions in contrast sensitivity and form perception ( 4 ). The am ount of veiling lum inance produced by headlam p glare is infl uenced prim arily by headlam p characteristicsâsuch as m ounting height, beam pattern, and misaimâand by the angle at which the glaring lum inance enters the eye. De si gn Issues Several ma thematical m odels have been developed that estimate the am ount of veiling luminance developed by a glare source (e.g., 1, 5, 6 ). These models show that veiling luminance is inversely proportional to the angle at which the glaring lum inance enters the eye relative to the forward gaze. Consequently, the glaring effects of exposure to light from oncoming headlamps can be significantly reduced by increasing the lateral separation of the opposing vehicles via wide me dian widths and independent alignm ents ( 7 ). Increasing the lateral distance between vehicles results in larger glare angles and therefore smaller veiling lu mi nances. Independent alignments can separate vehicles both horizontally and vertically, and in so me cases can eliminate exposure to oncom ing glare altogether. Other mi tigations include the installation of glare screens ( 8 ) and fixed roadway lighting ( 7 ). Glare screens are devices used prim arily in roadway me dians to shield driversâ eyes from exposure to glare from the headlights of oncom ing vehicles. Typical glare screens consist of solid partitions (with or without intermittent openings), expanded meta l mesh, knit polyester fabric, or vertical paddles oriented at an angle that blocks oncomi ng glare but allows lateral visibility. The cutoff angle for these types of glare screens is typically 20 degrees plus the degree of roadway curvature. Although no specific warrants have been established for installation of glare screens, ma ny factors should be considered when deter mi ning whether to install these screens. These factors in clude nighttim e crash rates (e.g., day-night ratio, average age of drivers in nightti me crashes, distribution of crash type, etc.), high traffic volume, public comments, high measured veiling luminance, road geometry, etc. Care must be given when designing and im plementing glare screens in order to avoid li mi ting the sight distance in horizontal curves. Fixed roadway lighting can reduce the effects of glare by: (1 ) increasing the visibility of objects and pedestrians and (2) increasing the overall adaptation level. Cr os s Re fe re nc es Characteristics of Effective Lighting at Intersections, 21-12 Nightti me Driving, 21-4 Ke y Re fe re nc es 1. Comm ission Internationale de lâEclairage (2002). CIE Equations for Disability Glare . CIE 1 46:2002. Vienna, Austria. 2. Adrian, W., & Bhanji, A. (1991) . Funda me ntals of disability glare: A formula to describe straylight in the eye as a function of glare angle and age. Proceedings of the First International Symposium on Glare, 185-193. New York: Lighting Research Institute. 3. Vos, J.J. (2003). On the cause of disability glare and its dependence on glare angle, age and ocular pigm entation. Clinical and Experimental Optometry, 86 (6), 363-370. 4. Adrian, W., & Topalova, R. (1991). Transient adaptati on process. A m odel to predict its effects in vision. Proceedings of the CIE 22nd Session 2 , 121â133. 5. Bhise, V.D., Farber, E.I., Saunby, C.S., Troell, G.M., Walunas, J.B., & Bernstein, A. (1977). Modeling vision with headlight s in a syste ms context. Society of Automotive Engineers International Automotive Engineering Congress and Exposition. 6. Farber, E., & Matle, C. (1989). PCDETECT: A revised version of the DETECT seeing distance model. Transportation Research Record, 1213, 11-20. 7. Mace, D., Garvey, P., Porter, R., Sch wab, R., & Adrian, W. (2001). Countermeasures for Reducing the Effects of Headlight Glare . Washington, DC: AAA Foundation for Traffic Safety. 8. Transportation Research Board (1979) . NCHRP Synthes is of Highway Practice 66: Glare Screen Guidelines. Washington, DC. 21-3 HFG LIGHTING Version 2.0
N IG HT TI ME D RI VI NG In tr od uc ti on Nighttime driving refers to particular challenges to motoristsâ visibility while driving in darkness on rural roads. The farthest distance at which drivers can see roadway features, objects in the roadway, or pedestrians ahead is li mi ted by the headlamp intensity, ambient lighting, and presence or absence of oncoming headlamp glare. Often in rural dr iv ing, the ambient illumination is of such low intensity that it has little effect on visibility. Illumination of problem areas along with appropriate signing can play a significant role in im proving safety when driving at night. De si gn Gu id e lin es The following treatm ents have been shown to reduce nighttime crashes and to promote speed reduction and stop compliance at rural intersections ( 1,2,3, 4 ). It should be noted that the Manual on Uniform Traffic Control Devices (MUTCD) and state and local policies should alway s be consulted before treatm ents are selected. Treatment Type Suggested Conditions for Use Benefits Sa fe ty lig ht in g ⢠Light conditions are dark ⢠High pedestrian traffic ⢠High average daily (or nightly) travel ⢠Areas with high crash history or high potential for cras hes ⢠Improved pedestrian and vehicle detection and recognition ⢠Earlier reduced sp eed at intersections ⢠Most effective for crash reduction Ad va nc e wa rn in g si gn s ⢠Intersection approach ⢠Sharp curve approach ⢠Potential for earlier reduced speed Ad va nc e wa rn in g si gn s wi th po st -m ou nt ed be ac on ⢠Intersection approach ⢠Sharp curve approach ⢠Areas with crash history or potential for crashes ⢠Beacon captures attention, implies urgency, and im proves sign conspicuity ⢠Potential for earlier reduced speed St op si gn wi th po st -m ou nt ed be ac on ⢠Intersection approach ⢠Intersections that do not warrant continuous lightin g ⢠Areas with crash history or potential for crashes ⢠Beacon captures attention and improves sign conspicuity ⢠Potential for earlier reduced speed Re fl ec ti ve st ri ps on St op si gn ⢠Unlighted or dark intersections ⢠Minor leg of âTâ intersection ⢠Improved conspicuity of the sign by increasing visible surface area Ra is ed pa ve me nt ma rk er s ⢠Light conditions are dark (with or without lighting) ⢠Curves and tangents (see Chapter 6) ⢠Improved visibility of lane when road surface condition is wet In te rs ec ti on fl as hi ng be ac on s ⢠Intersections where continuous lighting is not cost effective ⢠Pedestrian traffic ⢠Areas with crash history or potential for crashes ⢠Beacon captures attention and provides alert for upcoming intersection ⢠Potential for earlier reduced speed Ba sed Primarily on Ex pert Jud g ment Based Equally on Expert Judgment and Empirical Dat a Based Primarily on Em pirical Da ta HFG LIGHTING Version 2.0 21-4
Discussion Visibility during nighttime driving in rural environments can be challenging for drivers. Often there is little or no ambient lighting to enhance the illumination of the roadway or objects thereon. Visibility distance is limited to a threshold imposed by the luminous intensity of the headlamps, beyond which roadway features and objects or persons in the roadway are not visible due to insufficient contrast. Depending on headlamp characteristics and object reflectivity, visibility is generally limited to between 150 and 250 ft under clear, dry conditions (5, 6). However, the time required to react and stop under the best of conditions (i.e., short braking reaction time and hard deceleration) when driving at 55 mi/h can be 280 ft or more (7). Compounding this problem is the potential for increased stopping distance due to longer perception-reaction time caused by fatigue from prolonged rural driving. Drivers often underappreciate the visual challenges associated with driving in darkness for several reasons. First, drivers believe they can safely drive at unsafe higher speeds because (a) there is sufficient light from the headlamps to support lane keeping, and (b) it is relatively easy to see road signs, edge lines, delineators, and other vehicles on the road (6). Also, the central vision required for hazard detection and recognition is severely degraded at distances beyond the visibility threshold of the headlamps (6). Drivers may not understand the illumination pattern of their own headlamps (i.e., that the illumination provided by the headlamp is heterogeneous) and may therefore misjudge the visibility distance within various regions of headlamp illumination (8). Speed limits that are uniform between day and night lead drivers to assume that driving at the speed limit is safe even though it may not be possible to stop within the visibility distance of the headlamp (9). Finally, drivers seldom use their high-beam headlamps, even in situations where there are no oncoming vehicles or vehicles in the lane ahead (10). Because of these factors, drivers often are likely to be unprepared for a dangerous encounter while driving in darkness. Design Issues Fixed roadway illumination can improve visibility, reduce speed, and improve safety in rural areas that are identified as potentially hazardous or that have significant crash histories (e.g., 3, 4). Although lighting is the most effective mitigation for improving visibility, alternative treatments, such as signing, reflectors, and beacons, can enhance safety by reflecting more existing light to drivers or alerting drivers in advance of upcoming features. The warrant criteria for installing continuous lighting is usually based on an analysis of cost-effectiveness, considering installation, operation, and maintenance costs in addition to the cost associated with crashes (2, 3). The warrant criteria vary widely between states and research sources and include factors such as average daily travel, crash frequency, and night-to-day crash ratio. It may be appropriate to use a sign telling drivers to turn on their headlights when in the tunnel. Cross References Countermeasures to Improve Pavement Delineation, 6-10 Sign Design to Improve Legibility, 18-4 Key References 1. Brewer, M.A., & Fitzpatrick, K. (2004). Preliminary Evaluations of Safety Treatments on Rural Highways in Texas. College Station, Texas: Texas Transportation Institute. 2. Anderson, K.A., Hoppe, W.J., McCoy, P.T., & Price, R.E. (1984). Cost-effectiveness evaluation of rural intersection levels of illumination. Transportation Research Record, 996, 44-47. 3. Hallmark, S.L., Hawkins, N.R., Smadi, O., Kinsenbaw, C., Orellana, M., Hans, Z., & Isebrands, H.N. (2008). Strategies to Address Nighttime Crashes at Rural, Unsignalized Intersections. (IHRB Project TR-540; CTRE Project 05-220). Ames: Iowa State University Center for Transportation Research and Education. 4. Isebrands, H.N., Hallmark, S., Hans, Z., McDonald, T., Preston, H., & Storm, R. (2006). Safety Impacts of Street Lighting at Isolated Rural Intersections - Part II. (MN/RC-2006-35). St. Paul: Minnesota Department of Transportation. 5. Schiller, C., Sprute, H., Groh, A., Böll, M., & Khanh, T.Q. (2009). HID vs. Tungsten Halogen Headlamps: Driver Preferences And Visibility Distance (SAE Technical Paper 2009-01-0550). Warrendale, PA: Society of Automotive Engineers. 6. Owens, D.A., Francis, E.L., & Leibowitz, H.W. (1989). Visibility Distance with Headlights: A Functional Approach (Report No. 890684). Warrendale, PA: Society of Automotive Engineers. 7. Green, M. (2000). âHow long does it take to stop?â Methodological analysis of driver perception-brake times. Transportation Human Factors, 2(3), 195-216 8. Brooks, J.O., Goodenough, R.R., Tyrrell, R.A., Guirl, C., Moore, K., Klein, N., & et al. (2009). How well do drivers understand their own headlights? Proceedings of the Fifth International Driving Symposium on Human Factors in Driver Assessment, Training and Vehicle Design, 384-390. 9. Leibowitz, H.W., Owens, D.A., & Tyrrell, R.A. (1998). Assured clear distance ahead rule: Implications for nighttime traffic safety and the law. Accident Analysis and Prevention, 30(1), 93-99. 10. Mefford, M.L., Flannagan, M.J., & Bogard, S.E. (2006). Real-World Use of High-Beam Headlamps. (UMTRI-2006-11). Ann Arbor: University of Michigan Transportation Research Institute. 21-5 HFG LIGHTING Version 2.0
DAYTIME LIGHTING REQUIREMENTS FOR TUNNEL ENTRANCE LIGHTING Introduction This guideline provides recommendations for minimum lighting requirements at the entrances of tunnels under daylight conditions. Visibility of low-visual-contrast objects can be challenging for drivers due to glare, large differences in illumination, and visual adaptation issues associated with the tunnel entrance. The guideline information below provides initial illumination recommendations that can be used during the initial tunnel design stage to promote better visibility when entering tunnels. Design Guidelines The table below provides general recommendations for initial luminance design. More precise calculations are recommended once the tunnel design is well defined (from IESNA (1)). RECOMMENDED DAYTIME MAINTAINED AVERAGE PAVEMENT LUMINANCE LEVELS IN THE THRESHOLD ZONE OF VEHICULAR TUNNELS (LTH) Approach Characteristics Traffic Speed Driver Direction km/h mi/h North East-West South cd/m2 Open Road 100 80 60 60 50 40 250 220 180 310 260 220 370 320 270 Urban Tunnel 100 80 60 60 50 40 320 280 230 280 240 200 310 270 220 Mountain Tunnel 100 80 60 60 50 40 230 200 170 200 170 140 200 170 140 LIGHTING ZONES DURING TUNNEL APPROACH AND ENTRY Source: adapted from CIE (2). Based Primarily on Expert Judgment Based Equally on Expert Judgment and Empirical Data Based Primarily on Empirical Data HFG LIGHTING Version 2.0 21-6
Di scu ssi on Lighting of tunnel entrances requires special consideration because of how driversâ visual system s respond to the uni que light in g conditions that occur at these entrances. In particular, there are driver performance issues related to illu mi nation levels in tunnel entrances. The first issue is that glare fro m the bright visual zones surrounding the tunnel entrance when lit by daylight can make objects within the entrance more difficult to see than if there was no glare (e.g., at night) ( 1, 2 ). This can significantly decrease the detection distance for hazards in the tunnel entrance. The second issue is related to the first in that large differences in illumination between the tunnel entrance and surrounding zones can cause the entrance to be perceived as a âblack hole.â This can cause drivers to decelerate quickly or drive erratically and generally poses a safety risk ( 3 ). The third issue is visual adaptation, which occurs when drivers transition from the high light levels outside the tunnel to dimmer interior tunnel lighting ( 4 ). Driversâ sensitivity to low-visual-contrast hazards is generally reduced until their eyes are able to adapt to the lower light levels, leading to a corresponding decrease in detection distance. In most cases, driversâ eyes have sufficient time to make this adjustment before entering the tunnel. This i ssue, however, may require special consideration if posted speeds are high, which gives drivers less time to adapt to lower lighting conditions. De si gn Is su es Vehicle speed approaching the tunnel is an important consideration. Since drivers are assumed to be adapting to lower light levels as they approach the tunnel entrance, th eir travel speed affects the amount of time their eyes have to adjust to tunnel entrance illumination. At higher speed s, drivers will have less time to adjust (e.g., 13 s vs. 6.5 s for 40 and 80 km/h posted speeds, respectively), and significantly higher levels of tunnel illumi nation will be required to maintain adequate visibility ( 1 ). Consequently, if posted speeds approaching the tunnel are changed, then lighting requirements should be formally reexamined. The sky is a significant source of dayti me luminance, and the am ount of sky in driversâ field of view during the approach to a tunnel entrance can lead to an elevated adaptation level prior to entering the tunnel ( 1 ). The topography of the area surrounding the tunnel often affects the amount of sky that is visible, with flat topographies exposing large regions of sky and therefore substantial lu mi nances in the field of view, which elevates adaptation level. In general, the mo re sky that is visible in the fi eld of view prior to tunnel entry, the higher the surface luminance that is required in the tunnel entrance in order to maintain adequate visibility. Greater surface luminance is also required when large, bright surfaces surround the tunnel entrance (e.g., large retaining walls, rocks, and other highly reflective surfaces). Tunnel lighting requirem ents can be defined with regard to a comm on visual task (e.g., 2 ). Specifically, this involves the detection of a hazard in the middle of the driverâs lane an d requires that drivers be able to stop before reaching the hazard. In the CIE calculations for determining lighting requirem ents, the target is assumed to have a height and width of 20 cm and a reflectivity of 20%. The ray between the driver eye point (assumed to be 1.5 m above the roadway) and a low hazard on the road is the basis for computing the effect of the luminance of peripheral visual zones on driver visibility and adaptation. Counterbeam lighting appears to be more effective in making potential hazards easier to see because it increases the objectâs contrast relative to the background ( 3 ). The IESNA guidelines ( 1 ) suggest that lighting requirements can be reduced if counterbeam lighting is used in the transition zone. Regardless of the type of lighting configuration, AASHTO (5) recommends that the lighting should be as continuous as possible to minimize the stroboscopic effect produced by the spacing of the lu mi naries. When dr iv ing at the design speed, frequencies of 5 to 10 cycles per second have been shown to cause eye annoyance. Cr os s Re fe re nc es Countermeasures for Mitigating Headlamp Glare, 21-2 Characteristics of Effective Lighting at Intersections, 21-12 Ke y Re fe re nc es 1. Illu mi nating Engineering Society of North Am erica (IESNA) (2005). IE SN A Recommended Practice for Tunnel Lighting . ANSI/IES RP-22. New York. 2. Comm ission Internationale de lâEclairage (2004). Guide for the Lighting of Road Tunnels and Underpasses . CIE 88:2004. Vienna, Austria. 3. Blaser, P. (1990). Counterbeam lighting, a proven alternative for the lighting of the entrance zones of road tunnels. Transportation Research Record , 1287, 244-251. 4. Adrian, W.K., & Topalova, R.V. (1991). Visibility under transient adaptation. Transportation Research Record , 1327, 14-20. 5. AASHTO (2005). Roadway Lighting Design Guide . Washington, DC. 21-7 HFG LIGHTING Version 2.0
COUNT ER ME AS UR ES FO R IMPRO VI NG PEDES TR IA N CONSP IC UI TY AT CROSSW AL KS In tr od uc ti on Countermeasures for improving pedestrian conspicuity at crosswalk s refers to treatments that use flashing lights and beacons at midblock and intersection crosswalks. These lighting treatments do not necessarily improve visibility of pedestrians; rather, they are used to alert drivers to the presence of pedestrians in the crosswalk. The MUTCD ( 1 ) provides standards for im plementing in-pave m ent flashing lights, sight-mounted flashing beacons, and flashing LEDs mounted in pedestrian crossing signs (in-sign flashing lights). This guideline provides additional information for the effective use of these counterme asures. De si gn Gu id e lin es In -S ig n Fl as hi ng Li gh ts an d Si gn -M ou nt ed Fl as hi ng Be ac on s (s ee ex am pl es be lo w) ⢠Use either of these treatments to augment pavement markings and signs at uncontrolled crosswalks with heavy pedestrian and vehicle traffic, or that ma y not otherwise be clearly visible. ⢠Combine either of these treatments with in-pavement flashing lights to maximize driversâ awareness of pedestrian presence in the crosswalk. In-sign flashing lights should be coordinated to flash in synchronization with the in- pavement flashers. In -P av em en t Fl as hi ng Li gh ts ⢠To prom ote pedestrian safety, consider using yellow in -pavement flashing lights at uncontrolled crosswalks, in locations (e.g., midblock) where drivers are not expecting a crosswalk, or when there are ma ny other features in the surrounding environment that compete for driversâ attention. ⢠Use only in ma rked crosswalk s. Also, include applicable warning signs (e.g., yield/stop for pedestrians) to further enhance the effectiveness of the treatment. ⢠It is suggested that in-pavement flashing lights be used when traffic volu me s are between 5,000 and 30,000 vehicles per day and/or a mi nimu m of 100 pedestrians per day ( 8 ). ⢠In-pavement flashing lights should be active (flashing) only when a pedestrian is present as determ ined by either a pedestrian pushing a button or by sensors that detect pedestriansâ presence. ⢠Automated detection of pedestrians is preferred over ma nual pushbutton to activate the flashing lights. ⢠If auto ma ted detection is used, the sensing technology should minimize the occurrence of false and mi ssed detections. ⢠Flashers that protrude above the pavement surface should be located so that they do not pose a safety hazard to bicyclists. E XA MP LE S OF I N -P AV EM EN T F LA SH IN G L IG HT S , I N -S IG N F LA SH IN G L IG HT S , AN D S IG N -M OU NT ED F LA SH IN G B EA CO NS In -p av em en t fl as hi ng lig hts ( 2 ) In -s ig n fl as hi ng lig hts ( 3 ) Si gn -m ou nt ed fl as hi ng be ac on s ( 4 ) Photo on left provided by authors Ba sed Primarily on Ex pert Jud g ment Based Equally on Expert Judgment and Empirical Dat a Based Primarily on Em pirical Da ta HFG LIGHTING Version 2.0 21-8
Di scu ssi on In-pavement flashing lights, sign-m ounted flashing beacons, and flashing LEDs mounted in âPedestrian Crossingâ warning signs (in-sign flashing lights) have been shown to improve the safety at pedestrian crosswalks. These treatments are designed to alert drivers to the presence of pedestrians in the crosswalks or to ma ke the crosswalk itself more conspicuous. When these treatments are used to supplement signs and markings at crosswalks, they have been shown to reduce the number of evasive conflicts between drivers and pedestrians ( 4 ), increase the rate of mo toristsâ yielding to pedestrians ( 4, 5 ), increase the distance at which drivers apply their brakes ( 5 ), reduce mo toristsâ approach speed ( 6 ), and increase pedestriansâ perception of safety ( 7 ) in both day and nighttime driving. In-pavement flashing lights can be an attractive alternative to full signalization when the conditions are appropriate. The greatest improvements in safety generally occur in crosswalks with high pedestrian usage on roads with high average daily traffic. One source ( 8 ) recommends that in-pavement flashing lights be used when at least 100 pedestrians per day use the crosswalk and when average daily traffic (ADT) is between 5,000 and 30,000 vehicles per day. In-pavem ent systems, however, can be expensive to acquire, install, and ma intain re lative to other treatments. Consequently some jurisdictions (e.g., 9 ) recommend that in-pavement flashing lights be used only when mo re traditional treat ments prov e unsuccessful at sufficiently im proving safety. In-sign flashing LEDs or sign-m ounted flashing beacons may provide successful, lower cost alternatives to in-pavement flashing lights for crosswalks with lower ADT or pedestrian density. Dramatic improvements in driver behavior near crosswalks have been demonstrated when sign-m ounted flashing beacons or in-sign flashing lights are used in combination with in-pavement flashing lights. In one study ( 3 ) al mo st 90% of vehicles yielded to pedestrians when in-pavement flashers a nd sign-m ounted beacons were both present, 70% yielded with in-sign flashers only, and 18-25% yielded when there was no treatment. Si mi larly, another study ( 6 ) showed marked reductions in vehicle speed, pedestrian wait time, curb-to-cu rb duration of crossing, and disregarding pedestrians in the crosswalk when in-pavement flashing lights were used in concert with sign-mounted flashing beacons. De si gn Is su es To differentiate between an empty crosswalk and one with pedestrians present, in-pavement flashing lights should be active only when pedestrians are present in the crosswalk ( 1 ). Drivers who are repeatedly exposed to continually flashing lights may become accustomed to the m and eventually ignore them , particularly if the crosswalk is usually empty when they encounter it. Flashing lights can be activated either ma nually by pressing a pushbutton that indicates intent to cross, or autom atically using sensors (passive detection) at the cros swalk entrances. Passive detection is generally preferred over using a manual pushbutton because some pedestrians may not bother to press a pushbutton before crossing or they ma y be confused by the pushbutton because there is no corresponding signal indicating when to walk ( 8 ). However, this confusion can be m itigated by including signage to indicate the purpos e of the pushbutton (e.g., âPress button for crosswalk warning lightsâ ; 3 ). Because in-pavement flashing lights protrude above the street surface, they can present a potential safety hazard to bicyclists ( 5 ). Careful placement of the ma rkers where bicyclists (o r mo torcyclists) are not likely to ride and mi ni mi zing the height of protrusion should reduce this hazard. Cr os s Re fe re nc es Characteristics of Lighting that Enhance Pedestrian Visibility, 21-10 Methods to Increase Driver Yielding at Uncontrolled Crosswalks, 15-2 Ke y Re fe re nc es 1. FHWA. (2009). Manual on Uniform Traffic Control Devices for Streets and Highways. Wash ington, DC. 2. Van Derlofske, J., Boyce, P.R., & Gilson, C.H. (2003). Evaluation of in-pavem ent, flashing warning lights on pedestrian cros swalk safety. Transportation Research Board 82 nd A nnual Meeting Compendium of Papers [CD ROM]. 3. Davis, K.D., & Hallenbeck, M.E. (2008). Evaluation of Engineering Treatments and Pedestrian and Motorist Behavior on Major Arterials in Washington Stat e (WA- RD 707.1). Olym pia: Washington State Departm ent of Transportation. 4. Van Houten, R., Ellis, R., & Marm olejo , E. (2008). Stutter-flash light-em itting-diode beacons to increase yielding to pedest rians at crosswalks. Transportation Research Record, 2073 , 69-78. 5. Godfrey, D., & Mazzella, T. (1999). Success in redesigning main streets for pedestrians. Proceedings of the Sixth National Conference on Transportation Planning for Small and Medium-Sized Communities . Wa shingto n, DC: Transportation Research Board. 6. Prevedouros, P.D. (2001). Evaluation of In-Pavement Flashing Lights on a Six-Lane Arterial Pedestrian Crossing . Retrieved June 14, 2010 from http://www.eng.hawaii.edu/~panos/litegrd.pdf. 7. Ullm an, B., Fitzpatrick, K., & Trout, N. (2004). On-stre et pedestrian surveys of pedestrian crossing treatments. Proceedings of the ITE 2004 Annual Meeting and Exhibit . 8. Whitlock & Weinberger Transportati on, Inc. (1998). An Evaluation of a Crosswalk Warning System Utilizing In-Pavement Flashing Lights . Retrieved June 20, 2011 from http://www.safezonealert.co m. au/files/EvaluationCrosswalkWarningSystem UtilizingInPavem entLights.pd f. 9. Arnold, E.D., Jr. (2004). Development of Guidelines for In-Roadway Warning Lights. Final report (VTRC 05-R10). Charlottesville: Virginia Transportation Research Council. 21-9 HFG LIGHTING Version 2.0
C HARACTERISTICS OF LIGHTING THAT ENHANCE PEDESTRIAN VISIBILITY Introduction This guideline addresses characteristics of luminaires at midblock and intersection crosswalks as well as for general street lighting that will enhance the visibility of pedestrians in or near th e roadway. Factors that affect visibility under street lighting include intensity and color spectrum of the light source; reflectivity and color of the pedestrian clothing; reflectivity of the road surface; and whether the pedestrian is seen with periphera l or foveal vision. The characteristics addressed in this guideline include spectral power distribution (color) of the light source and luminaire location. Intensity of the light is an important characteristic that is covered in âCharacteristics of Effecti ve Lighting at Intersectionsâ on page 21 - 12. Design Guidelines ⢠Consider using luminaires with broad spectrum characteristics to promote longer detection distances and better recognition of pedestrians wearing a variety of clothing colors. ⢠Lighting a crosswalk with lamps of a color spectrum that differs from the overall road lighting can improve motoristsâ brightness perception, concentration, and search behavior through the crossing area. ⢠Luminaires should be located such that pedestrians in the cross walk are seen in positive contrast. This can be accomplished by placing luminaires 10 to 15 feet ahead of a crosswalk in each direction of vehicle travel. ⢠Luminaires placed ahead of the crosswalk should include a sharp cutoff that minimizes exposure of gla re to oncoming vehicles. LPS ( 1 ) HPS ( 2 ) LED ( 2 ) Induction ( 3 ) Examples of the color accuracy of objects illuminated by low pressure sodium (LPS), high pressure sodium (HPS), LED, and induction street lamps. In general, luminaires with broad spectrum characteristics (e.g., LED, induction , flourescent, and metal halide ) yield better visibility, color discriminability, and viewer acceptance compared to narrow spectrum lights (e.g., LPS and HPS). Placing luminaires 10 to 15 feet ahead of the crosswalk increases contrast by providing vertical illuminance ( 4 ) . Positive Contrast Negative Contrast Pedestrians are more visible when seen in positive contrast than in negative contrast ( 5 ) . Based Primarily on Expert Judgment Based Equally on Expert Judgment and Empirical Data Based Primarily on Empirical Data HFG LIGHTING Version 2.0 21-10
Di scu ssi on The issues associated with visibility of pedestrians at ni ght under street lighting are complex. Drivers mu st detect pedestrians under me sopic lighting levels, at which both the rod and cone receptors in the retina support vision ( 6 ). The peak sensitivity of the cones occurs in the yellow region of the spectrum, while the rod peak sensitivity is near the blue/green. In mesopic lighting, visual sensitivity is shifted toward the blue/green portion of the visible spectru m compared to vision under photopic (daytime) lighting, when the cones are the prim ary visual receptors. However, pedestrian detection often relies on peripheral vision, which is do mi nated by the rods, causing even further bias toward the blue. Consequently, the spectral power distribution (SPD) of the light source can have a considerable effect on the visibility of a pedestrian depending on clothing color and position relative to the driverâs forward gaze. Clothing that is similar in color to the lighting source is more highly visible than clothing of a contrasting color (e.g., under yellow light, a yellow shirt will appear to be brighter than a blue shirt will ). This suggests that a broad spectrum light source will likely prom ote superior visibility for pedestrians wearing a variety of colors. Various lamp technologies exhibit different spectral characteris tics: metal halide (MH) lamps cast a bluish light, while high- and low-pressure sodium lamps are biased toward the yellow portion of the spectrum. The SPD of the light source has been shown to affect pedestrian visibility. In one study ( 7 ), detection distances were similar for pedestrians wearing white clothing under both HPS and MH lamp sources. However, detection distances were greater with MH lamps than with HPS lamps when pedestrians were wearing denim. White fabric reflects all colors somewhat equally, so it is less sensitive than blue deni m to spectral bias in the light source. In contrast, denim reflects the blue light of the MH lamps while it absorbs mu ch of the yellow fro m an HPS la mp . Newer technologies, such as LED, fluorescent, and induction lamps, are likely to result in better visibility over a broader range of clothing colors because these lamps generally can be designed to have broad spectral distributions. One study ( 8 ) demonstrated that detection distances were longer when using several LED and induction lamp systems comp ared to a lower wattage HPS lamp even though the HPS illu mi nance was greater than any of the alternative lamp types. Color contrast can also play a role in im proving visibility. Lighting a crosswalk with la mp s of a color spectru m that differs fro m the overall road lighting can draw attention to the crosswalk and im prove mo toristsâ brightness perception, concentration, and search behavior through the crossing area ( 9 ). De si gn Is su es Pedestrians are more visible in positive contrast (i.e., the background is darker than the pedestrian) than they are in negative contrast (i.e., the background is lighter than the pedestrian) ( 5 ). Lum inaires placed 10 to 15 ft ahead of a crosswalk can improve contrast by providing vertical illu mi nance incident on the pedestrian that is stronger than the horizontal illuminance incident on the pavement behind the pedestrian ( 10 , 11 ). Bollard-mounted lights can also provide high-contrast vertical lu mi nance at a crosswalk. In a lighting simulation ( 10 ), bollard-m ounted lu mi naires were effective for providing superior vertical illu mi nation for visibility of pedestrians, but they also were found to be mo re glaring than more tradition al illu mi nation methods. Regardless of the lu mi naire type, the syste m sh ould be carefully designed to mini mi ze driversâ exposure to glare fro m the luminaire. Cr os s Re fe re nc es Characteristics of Effective Lighting at Intersections, 21-12 Ke y Re fe re nc es 1. Mutmansky, M., Gi vler, T., Garcia, J., & Clanton, N. (2010). Advanced street lighting technologie s assessm ent project â City of San Jose. Clanton & Associates. 2. Energy Solutions (2008). Demonstration Assessment of Light Emitting Diode (LED) Street Lighting. Host Site: City of Oakland, California . Washington, DC: Department of Energy. 3. Morante, P. (2008). Mesopic Street Lighting Demonstration and Evaluation Final Report. Groton, Connecticut: Groton Utilities. 4. Gibbons, R.B., Edwards, C.J., Willia ms , B., & Andersen, C.K. (2008). Informational Report on Lighting Design for Midblock Crosswalks (FHWA- HRT-08-053). McLean, VA: FHWA. 5. Hasson, P., Lutkevich, P., Ananthanarayanan, B., Watson, P., Knoblauch, R., & Nitzburg, M. (2002). Field test for lighting to improve safety at pedestrian crosswalks. Proceedings of the 16th Biennial Sy mposium on Visibility and Simulatio n . 6. Lewin, I. (1999). Lamp Color and Visibility in Outdoor Lighting Design , developed from a paper delivered to the 1999 Conference of the Institution of Lighting Engineers, Portsm outh, England. 7. Edwards, C.J., & Gibbons, R.B. (2008). Relationship of ve rtical illum inance to pedestrian visibility in crosswalks. Transportation Research Record, 2056 , 9-16. 8. Gibbons, R.B., Edwards, C.J., Clanton, N., & Mutmansky, M. (2010). Alternative lighting evaluations: m unicipality of Anchora ge. Transportation Research Board 90 th Annual Meeting Compendium of Papers [DVD] . 9. Janoff, M.S., Freedman, M., & Koth, B. (1977). Driver and pedestrian behavior - The effect of specialized crosswalk illum in ation. Journal of the Illuminating Engine ering Society, 6N (4), 202-208. 10. Bullough, J.D., Zhang, X., Skinner, N.P., & Rea, M.S. (2009). Design and Evaluation of Effective Crosswalk Illumination. (FHWA-NJDOT-2009- 003). Trenton: New Jersey Depart me nt of Transportation. 11. C hu, X. (2006). Pedestrian Safety at Midblock Locations. (CUTR BD544-16). Tallahassee: Florida Depart me nt of Transportation. 21-11 HFG LIGHTING Version 2.0
C HARACTERISTICS OF EFFECTIVE LIGHTING AT INTERSECTIONS Introduction Characteristics of effective lighting at intersectio ns refers to lighting characteristics that facilitate visibility at intersections while avoiding detrimental effects of glare from luminaires. Although vehicle head lamps provide some measure of illumination, additional fixed lighting is often required to provide light levels and contrast that are satisfactory for safe visibility at intersections. This guideline provides principles for improving visibility of pedestri ans, vehicles, roadway features, and obstacles at intersections. Design Guidelines ⢠Use a pole height, luminaire type, and luminaire cutoff pattern that will ensure adequate coverage of illuminance and uniformity of the light (see table below) throughout the intersection without exposing drivers to direct glare from the luminaire. ⢠Use the illuminance levels in the table below at intersections of continuously lighted streets with R2 or R3 pavement classifications. If lighting on an intersecting roadway is greater than the recommended value, the intersection illuminance should be increased p roportionally. ⢠Use the alternat iv e lighting layout in Figure B in areas with high pedestrian traffic ( 1, 2 ) . ⢠A partial lighting system can be utilized if the intersecting streets are not continuously lighted ( 1 ) . RECOMMENDED ILLUMINANCE FOR INTERSECTIONS Functional Classification Average Maintained Illumination at Pavement by Pedestrian Area Classification (Lux / fc) Uniformity E avg /E min High Medium Low Major/Major 34.0 / 3.4 26.0 / 2.6 18.0 / 1.8 3.0 Major/Collector 29.0 / 2.9 22.0 / 2.2 15.0 / 1.5 3.0 Major/Local 26.0 / 2.6 20.0 / 2.0 13.0 / 1.3 3.0 Collector/Collector 24.0 / 2.4 18.0 / 1.8 12.0 / 1.2 4.0 Collector/Local 21.0 / 2.1 16.0 / 1.6 10.0 / 1.0 4.0 Local/Local 18.0 / 1.8 14.0 / 1.4 8.0 / 0.8 6.0 Source: IESNA ( 1 ) A. Traditional layout â Good for illuminating conflict areas in the intersection, but poorer for visibility of pedestrian s . B. Alternative layout â B etter for visibility of pedestrian s , but harder to illuminate conflict areas in the intersection . Source: Gibbons, Edwards, Williams and Andersen ( 2 ) Based Primarily on Expert Judgment Based Equally on Expert Judgment and Empirical Data Based Primarily on Empirical Data HFG LIGHTING Version 2.0 21-12
Di scu ssi on A minimu m level of illumination is required in the driving environment for drivers to visually detect pedestrians, obstructions, intersection features, and other vehicles in order to safely cross or turn at an intersection at night. Although vehicle headlamps provide some measure of illumination, additional fixed lighting is often required to provide light levels and contrast that are satisfactory for sa fe visibility at intersections. Most sources agree that the addition of illumination at an intersection increases visibility and enhances safety (e.g., 3, 4, 5 ), and studies have shown that in some rural intersections as few as one or two lu mi naires can provide safety benefits ( 3, 6 ). Lum inaries are relatively expensive to install and maintain, however, and warranting criteria for the installation of lighting vary widely between jurisdictions. Nonetheless, well-designed lighting at critical intersections can be cost effective when considering the cost of crashes against the operating costs of the lighting. In one study ( 7 ), it was estimated that the payback for the addition of lighting woul d occur with in as little as one year using HPS lighting (although HPS is not the lighting source preferred by drivers, visibility is still likely to be better with HPS than with no lighting). One methodological approach ( 8 ) for warranting illumination of isolated rural intersections is based on geometric, operational, environm ental, and collision factors and uses ra tings and weights to assess if full or partial illu mi nation is warranted. The critical factors determining the need for illu mi nation are traffic volu mes, ni ghttime collisions attributable to lack of lighting, and the extent of raised channelization. De si gn Is su es Three met hods are described in the RP-8-00 standards ( 1 ) for the m easurement and specification of light levels from roadway lum inaires: (a) the luminance me thod, (b) the illuminance me thod, and (c) the sm all target visibility method. Each of these methods has advantages and disadvantages. The luminance method measures the light reflected from the road surface to the driverâs eye. This me thod is prefe rred by som e jurisdictions (e.g. , 9 ) for measuring tangent sections because it directly m easures the light that the eye sees. However, the lu mi nance met hod is im practical for use at intersections because the elevated lighting levels at the intersection skew the average luminance value used in the veiling luminance calculations ( 9 ). Likewise, the small target visibility method requires veiling lu mi nance calculations to determ ine adaptation luminance. The illuminance meth od is suitable for desi gni ng lighting at intersections because it measures the amount of light incident on the roadway surface and is therefore independent of the observer and road reflectance properties. The luminaire mast height, in combination with the beam pattern of the light source, affects the coverage, uni formity, and intensity of the illuminance measured at the pavement. Higher mast heights generally provide better coverage (e.g., mo re uniform ity over a larger area) but at the expense of intensity. The results of a si mu lated lighting study ( 10 ) suggest that, to optimize lighting levels and coverage, a preferred lighting configuration includes luminaires with 50-foot mast heights. These luminaires should be mounted as close as possible to both intersecting centerlines in the intersection without entering into any clear zone. However, one disadvantage of a taller mast is the increased opportunity for exposing drivers to glare. Luminaire and geometric characteristics (e.g., luminaire cutoff pattern, vertical curvature approaching the intersection, etc.) should be considered when designing both the ma st height and th e lighting in general. Cr os s Re fe re nc es Characteristics of Lighting that Enhance Pedestrian Visibility, 21-10 Ke y Re fe re nc es 1. Illum inating Engine ering Society of North America (2000). American National Standard Practice for Roadway Lighting (RP-8-00 Reaffirmed 2005) . ANSI/IESNA RP-8-00. New York. 2. Gibbons, R.B., Edwards, C.J., Willia ms , B., & Andersen, C.K. (2008). Informational Report on Lighting Design for Midblock Crosswalks (FHWA- HRT-08-053). McLean, VA: FHWA. 3. Green, E.R., Agent, K.R., Barrett, M.L., & Pigman, J.G. (2003). Roadway Lighting and Driver Safety . (KTC-03-12/SPR247-02-1F). Lexington: Kentucky Transportation Center. 4. Isebrands, H.N., Hallmark, S., Hans, Z., McDonald, T., Pres ton, H., & Storm, R. (2006). Safety Impacts of Street Lighting at Isolated Rural Intersections -P art II . (MN/RC-2006-35). St. Paul: Minnesota Depart me nt of Transportation. 5. Hallmark, S.L., Hawkins, N.R., Sm adi, O., Kinsenbaw, C., Orellana, M., Hans, Z., & Isebrands, H.N. (2008). Strategies to Address Nighttime Crashes at Rural, Unsignalized Intersections. (IHRB Project TR-540; CTRE Project 05-220). Ames: Iowa State University Center for Transportation Resear ch and Education. 6. Rockwell, T.H., Ba la , K.N., & Hungerford, J.C. (1976). A Comparison of Lighting, Signing, and Pavement Marking Methods for Detecting Rural Intersections at Night. (OHIO-DOT-08-76). Columbus: Ohio State University. 7. Box, P.C. (1989). Major road accident reduction by illumination. Transportation Research Record, 124 7 , 32-38. 8. Gibbs, M., Shaflik, C., & Zein, S. (2001). Illumination of Isolated Rural Intersections. Ottawa: Transportation Association of Canada. 9. McCorm ic k Rankin Corporation (MRC) and Gabriel Design (2009). Right-of-way Lighting Polic y (Document No. 21-10). Ottawa, Ontario: City of Ottawa. 10. Kinzenbaw, C. (2007). Effectiveness of intersection lighting. 2007 Transportation Scholars Conference. Am es: Iowa St ate University. 21-13 HFG LIGHTING Version 2.0
