National Academies Press: OpenBook

Applications of Illuminated, Active, In-Pavement Marker Systems (2008)

Chapter: Chapter Two - State of the Technology

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Suggested Citation:"Chapter Two - State of the Technology." National Academies of Sciences, Engineering, and Medicine. 2008. Applications of Illuminated, Active, In-Pavement Marker Systems. Washington, DC: The National Academies Press. doi: 10.17226/14182.
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Suggested Citation:"Chapter Two - State of the Technology." National Academies of Sciences, Engineering, and Medicine. 2008. Applications of Illuminated, Active, In-Pavement Marker Systems. Washington, DC: The National Academies Press. doi: 10.17226/14182.
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Suggested Citation:"Chapter Two - State of the Technology." National Academies of Sciences, Engineering, and Medicine. 2008. Applications of Illuminated, Active, In-Pavement Marker Systems. Washington, DC: The National Academies Press. doi: 10.17226/14182.
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Suggested Citation:"Chapter Two - State of the Technology." National Academies of Sciences, Engineering, and Medicine. 2008. Applications of Illuminated, Active, In-Pavement Marker Systems. Washington, DC: The National Academies Press. doi: 10.17226/14182.
×
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Suggested Citation:"Chapter Two - State of the Technology." National Academies of Sciences, Engineering, and Medicine. 2008. Applications of Illuminated, Active, In-Pavement Marker Systems. Washington, DC: The National Academies Press. doi: 10.17226/14182.
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Suggested Citation:"Chapter Two - State of the Technology." National Academies of Sciences, Engineering, and Medicine. 2008. Applications of Illuminated, Active, In-Pavement Marker Systems. Washington, DC: The National Academies Press. doi: 10.17226/14182.
×
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Suggested Citation:"Chapter Two - State of the Technology." National Academies of Sciences, Engineering, and Medicine. 2008. Applications of Illuminated, Active, In-Pavement Marker Systems. Washington, DC: The National Academies Press. doi: 10.17226/14182.
×
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Suggested Citation:"Chapter Two - State of the Technology." National Academies of Sciences, Engineering, and Medicine. 2008. Applications of Illuminated, Active, In-Pavement Marker Systems. Washington, DC: The National Academies Press. doi: 10.17226/14182.
×
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Suggested Citation:"Chapter Two - State of the Technology." National Academies of Sciences, Engineering, and Medicine. 2008. Applications of Illuminated, Active, In-Pavement Marker Systems. Washington, DC: The National Academies Press. doi: 10.17226/14182.
×
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Suggested Citation:"Chapter Two - State of the Technology." National Academies of Sciences, Engineering, and Medicine. 2008. Applications of Illuminated, Active, In-Pavement Marker Systems. Washington, DC: The National Academies Press. doi: 10.17226/14182.
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9This chapter describes the state of illuminated, active, IPM technology, including technology characteristics, standards and guidelines for use, and notable experiences from histor- ical IPM system applications. TECHNOLOGY CHARACTERISTICS Both the physical characteristics (i.e., housing, illumination source, etc.) and the operational characteristics (i.e., system activation, operation mode, etc.) of IPM systems are de- scribed here. Physical Characteristics IPM systems generally comprise an illumination source sur- rounded by a protective housing and lens, a power source, and a system controller in a protective enclosure. The design and features of the various components may vary signifi- cantly depending on the type of application. Illumination Source Both incandescent/halogen lamps and light-emitting diodes (LED) have been commonly used as light sources in IPM systems. Laser and electroluminescence technology has also been considered for use; however, each has respective limi- tations preventing widespread application. The earliest IPM systems, used primarily for airport runway/ taxiway path lighting, relied on halogen lamps as the light source. Halogen lamps often experienced water condensation and broken filaments (most likely caused by heavy vehicle traffic over the units), resulting in a need for frequent replace- ment (Boyce and Van Derlofske 2002). To overcome the noted shortcoming with halogen lamps, manufacturers moved toward the use of LEDs in traffic con- trol and in-roadway applications. The use of LED technology in traffic control devices (e.g., hazard identification beacons, traffic signals, pedestrian signals, and dynamic message signs) spans several decades. Noted benefits of LED technology in- clude lower power consumption, a smaller footprint, and less maintenance as compared with incandescent lamps (Finkel 1996). The useful life of an LED is purported to be up to 10 times the expected life of an incandescent lamp when used in a flash mode. Baker (2002) reported an estimated expected life of 10 years and 3 years, respectively, for LEDs and halo- gen lamps. In IPM system applications, the number of individual LEDs displayed in one direction can typically vary from 1 to 12. The LEDs are typically low-voltage, high-intensity sources, but many vendors offer the capability to adjust intensities using onboard photoelectric sensors or through external con- trollers depending on the ambient light characteristics (e.g., automatically dimming at night). This flexibility in lumi- nous intensity, combined with low power consumption and extended useful life, has resulted in LEDs emerging as the favored light source for IPM systems. Considering alternative light sources, Hagiwara et al. (1996) evaluated the use of laser beams to improve lane delineation in fog. Although laser beams provided sharply visible lines in fog, visibility is significantly affected by the amount of ambient lighting and the luminous intensity and viewing angle of the laser. Use of this technology also requires a mechanism to prevent road users from viewing the laser beams directly. A second alternative light source that has received some focus is electroluminescence technology. This technology is energy efficient, but requires high voltage for operation. Patangia and Radnayake (2004, 2007) compared the perfor- mance of barrier-mounted LEDs with electroluminescence technology in enhancing night visibility for road users in work zones. During an initial phase of the study, Patangia and Radnayake (2007) found that, with a solar powered assembly, the LEDs outperformed the electroluminescence technology with respect to field hardiness and luminous in- tensity. Using a modified electroluminescence technology with a direct-mount solar unit, the LEDs continued to out- perform the electroluminescence technology. In a road user survey, nearly three-quarters of respondents preferred the LEDs because of their brightness. Housing and Lens To minimize damage and subsequent replacement costs, light sources are encased in a protective housing. The housing typically measures no more than 6 in. along its largest dimen- sion. Housing materials have commonly been made of plastic, CHAPTER TWO STATE OF THE TECHNOLOGY

although newer markers are more frequently made of alu- minum or stainless steel for improved durability. One vendor advertised a plastic housing that “self-healed” when deformed by a snowplow, although no field evidence was provided. Lens materials commonly include polycarbonate or boron and glass. Some vendors include a passive retroreflective lens (i.e., a prismatic surface that reflects external light sources) in addition to active illumination to provide fail-safe opera- tion should the IPM system lose power. Power Source IPM systems can derive power to operate through hardwired electrical connections, inductive wireless connections, or through solar technology. Further, IPM systems can be con- figured in series or in parallel. Baker (2002) identified the fol- lowing three primary power/installation combinations used by IPM system vendors: • Series AC operation, which relies on halogen lamps (6.6 amp, 7 volts, 50 watt, or other light source) that are wired in series, equalizing voltage to each lamp (approx- imately 7 volts). Halogen lamps are extremely bright; in most installations, the lamps are dimmed to about 20% in faded light or dark conditions. • Parallel inductive-powered low-voltage DC operation, which relies on high-intensity LEDs that are induc- tively powered from a buried cable; the power trans- fer occurs wirelessly from a buried conductor to the marker. The system voltage depends on the length of the cable; a 24-marker installation would require 1 amp, 20 volts. • Parallel low-voltage DC operation, which relies on high- intensity LED (1.2 watts) with a system voltage ranging from 6 to 32 volts DC. In parallel, the system voltage is increased to compensate for voltage drop. Power sources for IPM systems must comply with National Electrical Code (NEC). Most vendors have assessed their IPM systems and components for conformance to the NEC. Baker (2002) suggested the need for public agency oversight, citing NEC Articles 240, 250, 411, 620, 720, and 725 as they apply to IPM systems. To date, hardwired electrical connections and inductive wireless connections have outperformed IPM systems relying on solar technology. Benefits of solar-powered IPM systems include the ease and flexibility of installation, particularly for remote areas. Green (2002) reported a cost for surface-mount, solar-powered markers featuring LED illumination ranging from approximately $30 to $80 each (2001 dollars). Disad- vantages relate to the compromised luminous intensity (e.g., magnitude and consistency) when compared with hardwired or inductive IPM systems. Continued advancements in solar technology may make this a more viable IPM system power source in the future. 10 System Controller and Enclosures IPM system controllers are typically housed in a protective cabinet or enclosure. For stand-alone IPM systems, the cabinet may contain a power and lighting control unit with a keypad and liquid crystal display (LCD), circuit breakers, an AC/DC transformer or a photoelectric sensor (as necessary), and slack cable. Battery backup capability is recommended. The cabinet is usually pole-mounted, but may also be located on the ground. A metal conduit connects the ground box and cabinet. If the IPM system is used in conjunction with other warning, guid- ance, regulatory, or illumination systems, the IPM system components could be housed in a traffic signal cabinet or other combined equipment enclosure. Examples do exist for state-level standards and guidance related to IPM system enclosure requirements. The California Department of Transportation (Caltrans) provides the fol- lowing specifications for in-roadway warning light (IRWL) equipment enclosures for crosswalk applications: IRWL equipment enclosures shall be Type G controller cabinets, and shall be in accordance with Section 86 2.11, “Service,” of the Standard Specifications. The IRWL equipment enclosure shall be designed for outdoor use and have a dead front panel and hasp for padlocking of the cover. Painting of IRWL equip- ment enclosures shall be in accordance with Section 86 2.16, “Painting,” of the Standard Specifications. IRWL equipment enclosures shall contain a power supply, controller unit compat- ible with IRWL operation, flasher unit, circuit breakers, terminal blocks, wiring, and electrical components for operation of the IRWL system. Installation Installation of IPM systems generally includes placement of the electrical cable and conduit to power the system and place- ment of the markers. For placement of the electrical wires, a common method requires saw-cutting a 3/8 in. to 1/2 in. groove in the pavement. A larger cut is required to accommodate a larger-diameter conduit. The resulting saw cut should be clear of debris and moisture. The electrical cable and/or conduit is placed in the saw cut and typically covered with epoxy. For inductive IPM systems, both the conduit and node assembly are placed in the saw cut and sealed with epoxy. It is important to provide enough depth to the saw cut to adequately recess and protect the electrical conduit. Individual solar-powered IPM units do not require burying of cable or conduit. Various methods are used for placement of markers. Mark- ers can be recessed in the pavement through coring or milling methods. Markers can also be affixed directly to the pavement surface using various adhesives. Recessed markers are less prone to pop-offs but require additional effort during the installation process. In cold regions, where snowplowing is seasonally required, use of recessed markers is necessary. Also, the performance of marker adhesives, particularly in unusually cold or hot temperatures, can have a significant effect on pop-off frequency. Each IPM system vendor provides

11 more detailed installation instructions that are tailored to its specific product. Operational Characteristics IPM systems provide significant flexibility in operation. Op- erational characteristics described here relate to system acti- vation and modes of operation (e.g., steady burn versus Flashing and chase sequences). System Activation Activation of IPM systems relies on either manual methods, where the system is activated directly by the user, or passive methods, where the system is activated automatically through some type of sensor input. Manual activation is most commonly achieved, particu- larly for pedestrian crosswalk applications, through a push- button system. An example of a manual push-button system is provided in Figure 1. Signage is placed in proximity to the push button to alert the pedestrian that action is required to activate the system. Although push-button systems are often favored by public agencies because of their low cost, it was anecdotally reported that pedestrians will only use a push- button system 60% of the time (M. Harrison, personal com- munication, July 2007). Additionally, the use of a push-button system makes pedestrians more aware of the system, possibly giving the pedestrian a false sense of security when crossing the roadway. Historically, a broader array of methods has been used to provide passive activation of IPM systems including: • In-ground sensors, • Motion sensors, • Visual image video detection systems (VIVDS), • In-pavement loop detectors, • Integration with traffic control devices, and • Road-weather information systems (RWIS). A common type of in-ground sensor, also used for pedes- trian crosswalk applications, includes pressure mats with piezoelectric sensors (see Figure 2). When the piezoelectric sensors are compressed by the presence of a pedestrian, the IPM system is activated. The pedestrian may or may not be aware that the system has been activated by the pressure mat. An alternative to in-ground sensors, motion sensors, may also be used to detect pedestrians entering or in a crosswalk. Motion sensors use light, radar, ultrasonic sound waves, in- frared waves, or microwaves to detect motion in a predefined area. A common motion sensor system uses rigid, upright posts or bollards and projected light across crosswalk entrances (see Figure 3). A set of two bollards is placed on each side of the en- trance to a crosswalk. Each bollard contains either a light trans- mitter or sensor or both devices to detect movement between the posts. When a pedestrian steps between the bollards, the beam of light is broken, signaling activation of the IPM system. Multiple beams of light projected between the bollards can be used to help determine the direction of travel of the pedestrian. VIVDS, capable of sensing a change in the background image of a particular view, provide a more sophisticated pas- sive activation system. In pedestrian crossing applications, a sensor detects a change in pixel configuration when a pedes- trian enters the viewfinder of a video detection unit. This sub- sequently alerts the IPM system that a pedestrian is waiting FIGURE 1 Push-button activation system for smart crosswalks (Courtesy: LightGuard Systems, Inc.). FIGURE 2 Pressure mat activation system (Courtesy: SmartStud Systems).

to cross. These systems are more commonly used to detect vehicles on traffic signal approaches. To date, their use for IPM system activation has been limited. Similarly, in-pavement loop detectors have been more commonly used in more traditional vehicle detection appli- cations such as detecting vehicles on traffic signal approaches and detecting vehicles on main lanes or entry ramps. This technology can also be used to detect a vehicle’s presence or speed as it approaches an IPM system. Speed-dependent IPM system applications include horizontal curves, tunnels, free- way exit or entry ramps, merge areas, or construction work zones. IPM systems have the potential to enhance the regulatory ability of other traffic control devices including traffic sig- nals, heavy-rail or light-rail warning signals, or school-zone flasher systems. RWIS have been used to activate IPM systems in response to adverse weather conditions. The intention of RWIS/IPM systems is to detect and alert road users of weather conditions that can limit sight distance or pose a significant driving haz- ard. Such systems have been most commonly used to miti- gate the effects of fog, ice, or snow. Depending on the application, each activation type has distinct advantages and disadvantages. Manual activation methods typically cost the least, but require action from the road user to be effective. Passive activation methods are more discrete, neither alerting the road user to the system nor providing a false sense of security; however, they may suffer a high frequency of “false positives” and “misses.” Pedestrian crosswalk experience suggests that motion sen- sors using microwave technology suffer a higher rate of false positives, particularly during rainy conditions (Huang 2000; Boyce and Van Derlofske 2002). Boyce and Van Derlofske 12 (2002) attributed an increase in vehicle speed and vehicle– pedestrian conflicts over time to false activation of the microwave-based motion sensor activation system and rec- ommended installation of a manual activation system. Con- versely, Whitlock and Weinberger (1998) recommended a passive activation system over an existing manual push-button system. Bollard activation systems, using projected light, have shown greater success. Huang et al. (1999) reported a 100% activation rate when pedestrians were present. Operation Modes Depending on the manufacturer, IPM systems offer a range of features that have the potential to enhance roadway oper- ations. Marker color changes can be used to indicate regula- tory action required by the road user (i.e., markers show red illumination when vehicles are required to stop). Varying flash rates (including steady burn) can indicate the level of hazard, and “chase” sequences can direct the road user to re- duce or increase speeds. Common IPM system marker colors include white, amber, red, green, and blue. Using LED illumination technology, IPM system markers can illuminate the same color in all directions, can alternate colors (i.e., all markers show red illumination when vehicles are required to stop but return to green or white when vehicles are permitted to travel), or can illuminate two different colors by direction (i.e., to indicate wrong way travel with white in one direction and red in the other). IPM systems can be operated in a steady-burn state or in a flashing mode, continuously or intermittently. The flashing mode may be triggered by a detected hazard (i.e., when up- stream speed sensors detect a vehicle traveling too fast for a curve or when RWIS detects fog conditions) and may, de- pending on the manufacturer, provide an adjustable increas- ing flash rate consistent with increasing danger (as long as the flash rate remains within an acceptable range). More sophisticated IPM systems offer forward or reverse “chase” sequencing (i.e., adjacent markers are sequentially illuminated giving the effect of moving light along the path). This feature is intended to improve speed-related roadway operations by pacing traffic at a consistent and appropriate speed for conditions. Chase sequencing has been used to maintain or reduce vehicle speeds in fog-prone areas and to reduce vehicle speeds on exit ramps. Other potential applica- tions for chase sequencing include horizontal curves, tunnels, merge areas, or construction work zones. When IPM systems are operated in a flash or chase mode, the frequency must operate below 5 flashes per second or more than 30 flashes per second. The flash rate should not be between 5 and 30 flashes per second owing to the possibility of inducing epileptic seizures in some individuals. FIGURE 3 Bollard motion sensor activation system (Courtesy: LightGuard Systems, Inc.).

13 STANDARDS AND GUIDELINES FOR USE Given the novelty of IPM system use on public roadways, little direction in the form of standards or guidelines is avail- able to support proper installation, operation, and maintenance of the systems. At the federal level, the Manual on Uniform Traffic Control Devices (MUTCD) (2004) provides standards, guidance, options, and support for traffic control devices in the United States. State officials either wholly adopt the standards defined in the MUTCD or develop unique state-level standards. Some countries outside of the United States have developed their own IPM system standards and guidelines. Federal Standards and Guidelines Although the MUTCD provides significant general guidance related to traffic control devices (e.g., signs, markings, and highway traffic signals), this reference contains few explicit standards, guidance, or options for IPM system use. Federal standards and guidelines for the installation, operation, and maintenance of IPM systems were developed as recently as 2000, with a focus on pedestrian crosswalk applications. The MUTCD defines “in-roadway lights” as: “A special type of highway traffic signal installed in the roadway surface to warn road users that they are approaching a condition on or adjacent to the roadway that might not be readily apparent and might require the road users to slow down and/or come to a stop” (MUTCD, Section 4A-3, 2004). Section 4L.01 Application of In-Roadway Lights of the MUTCD states that “in-roadway lights shall not exceed a height of 0.75 inches above the roadway surface” but pro- vides more flexibility in flash rates, stating that “the flash rate for in-roadway lights may be different from the flash rate of standard beacons” (MUTCD, Section 4L.01, 2004). Specific to pedestrian crosswalk applications, “Section 4L.02 In-Roadway Warning Lights at Crosswalks” of the MUTCD contains standards related to the installation and op- eration of IPM systems. In summary, IPM systems shall • Be installed only at marked crosswalks with applicable warning signs (not at crosswalks controlled by YIELD signs, STOP signs, or traffic control signals); • Be installed on both sides of the crosswalk, spanning its entire length; • Initiate operation based on pedestrian actuation and cease operation at a predetermined time after the pedes- trian actuation or, with passive detection, after the pedestrian clears the crosswalk; • Display a flashing yellow signal indication, with a flash rate of not less than 50 and not more than 60 flash periods per minute (flash rates between 5 and 30 flashes per sec- ond might induce epileptic seizures and shall not be used); • Be installed to meet minimum spacing requirements: – A minimum of two lights on the approach side of the crosswalk on one-lane, one-way roadways; – A minimum of three lights on both sides of the cross- walk on two-lane roadways; and – A minimum of one light per lane on both sides of the crosswalk on roads with more than two lanes; and • Be installed in the area between the outside edge of the crosswalk line and 10 ft from the outside edge of the crosswalk, facing away from the crosswalk if unidirec- tional or away from and across the crosswalk if bidirec- tional (an optional, additional yellow light indication visible to pedestrians in the crosswalk is permitted to indicate to pedestrians that the in-roadway lights are in- deed flashing as they cross the street). Additional guidance provided in this section relates to pedes- trian walking speeds and the subsequent period of IPM system operation. A normal walking speed of 4 ft per second or less should be used, depending on the nature of the pedestrian pop- ulation (e.g., a high proportion of elderly or wheelchair-bound pedestrians suggests a lower walking speed and longer period of IPM system operation). Furthermore, depending on the length of the crosswalk and presence of a median, sufficient width for pedestrians to wait and median-mounted pedestrian actuators may be required. In addition, Section 4L.02 recom- mends installing the IPM system markers in the center of each travel lane out of the normal vehicle tire path. For non-crosswalk applications of IPM systems, experi- mental approval may be sought and granted by the FHWA. One benefit of IPM system implementation under FHWA “experimental” status includes a reduced risk of liability for the requesting agency (i.e., in the event of deaths, injuries, or property damage, attributable to a nonstandard device or ap- plication). Additionally, improved evaluation can lead to changes in the MUTCD and widespread benefits to agencies and motorists. Note that Section 4L of the MUTCD classifies IPM sys- tems as a type of traffic signal rather than a pavement marker, delineator, illumination source, etc. This classification is likely attributable to the nature of the application considered; at pedestrian crosswalks, IPM systems function to alternately stop or permit traffic to proceed depending on pedestrian presence. Similarly, a highway traffic signal alternately stops or permits traffic to proceed depending on vehicle or pedes- trian presence. Other types of IPM system applications, such as horizontal curve or adverse weather warning, multiple-turn lane or tunnel guidance, or vehicle and truck inspection point illumination may be more appropriately categorized as pave- ment marking, delineator, or illumination source, respectively. In Section 1A.13 of the MUTCD, which provides a broader definition of terms, IPM systems are explicitly defined as not being highway traffic signals. This breadth of IPM system application and subsequent function suggests a similar re- quired breadth in related standards and guidelines. Table 1 summarizes MUTCD chapters or sections that currently pro- vide some related direction or would require future modifi- cation to better address IPM system use.

State-Level Standards and Guidelines Preceding the standards developed for inclusion in the MUTCD, Caltrans first issued guidelines and standards for the installation of IPM systems in 1998, again with a focus on pedestrian crosswalk applications. The development of these standards and guidelines followed several years of IPM system testing and evaluation. Current standards and guidelines have been updated to reflect and reference changes in the MUTCD. Example language related to IPM system operation follows: Flasher units for IRWLs shall be installed in IRWL equipment enclosures. Flasher units shall indicate when the IRWL is activated. The flash rate shall be between 50 and 60 flashes per minute. The flash rate and period for the IRWL shall conform with Chapter 4L of the California MUTCD. The flash rate shall conform to the requirements in Section 8.3.3 of the National Electrical Manufacturers Association Standards Publications No. TS 1 Traffic Control System. The minimum pedestrian crossing time shall be based on a walking speed of 4 feet per second. International Standards and Guidelines One of the more comprehensive guides for IPM system use, Recommendation for Use of Active Marking, was published by the Province of Noord-Holland in the Netherlands in 2005. This guide details: (1) appropriate applications of IPM systems; (2) the advantages and disadvantages of these sys- tems; (3) various functional and technical requirements in- cluding light source and housing, light color, light intensity, aperture angles, and placement; and (4) a decision tree to de- 14 termine the appropriateness of IPM systems compared with conventional marking, delineation, and illumination systems. This guide also includes a detailed example application of these principles at a horizontal curve section. Applications The Dutch suggest that IPM systems are appropriate for use in any situation where road user lane-tracking ability could be enhanced, and are particularly beneficial at horizontal curves. The Dutch guidelines recognize that because of the inherent low-light yield capability, IPM systems are not recommended for determining the position of the road user in relation to other vehicles, recognizing foreign objects on the road sur- face, or recognizing vehicles or people. Advantages and Disadvantages Advantages of IPM systems, as reported by the Dutch, include increased traffic safety, increased road user comfort, reduced light pollution and carbon dioxide emissions, the potential for installation in remote areas (not connected to an electrical grid) through the use of solar technology, elimination of the need for transition segments (low-light output requires no adaptation time for the road user when changing from illu- minated to nonilluminated segments, or vice versa), reduced residual materials at the end of the life cycle as compared with conventional lighting, and typically lower costs as com- pared with conventional lighting. Applicable MUTCD Standards and Guidance Warning School zones 7B.11 School Speed Lim it Assembly 7C.03 Crosswalk Markings Construction zones 6D.03 Worker Safety Considerations 6F.73 Raised Pavem ent Markers Highway-rail crossings 8B.06 Turn Restrictions During Preem ption 8B.21 Stop Lines 10C.23 Pavem ent Markings Horizontal curves 3D.02 Delineator Design 3D.03 Delineator Application 5E.03 Edge Line Markings Adverse weather Guidance Multiple-turn lanes 3D.02 Delineator Design 3D.03 Delineator Application Merge locations 3D.02 Delineator Design 3D.03 Delineator Application Tunnels 3D.02 Delineator Design 3D.03 Delineator Application 5E.04 Delineators Regulation Intersection stop bars 8B.21 Stop Lines Left-turn restrictions 8B.06 Turn Restrictions During Preem ption Illumination Vehicle/truck inspection points None Environmentally sensitive areas None TABLE 1 APPLICABLE MUTCD STANDARDS AND GUIDANCE

15 Disadvantages of IPM systems include the need to close the road completely during construction or maintenance if the IPM system is installed along the centerline (construction or maintenance of conventional lighting systems typically allow one lane to remain open), the loss of IPM system com- ponents when the road surface is repaired or removed, and potentially higher costs as compared with conventional light- ing if hardwired IPM systems are installed on multiple lane roadways (Recommendation . . . 2005). Functional and Technical Requirements With respect to light sources and housings for IPM systems, the Dutch provide the following recommendations (Recom- mendation . . . 2005): • Light sources should have a lifespan equaling at least that of conventional pavement marking equipment, and preferably that of road surfaces; “only LED technology currently meets this criteria.” • The protective housing should be composed of high- quality synthetic material, which can be milled out at the end of its lifespan or with replacement of the asphalt; the supplier must demonstrate that the housing has a dura- bility lasting at least 20 years. • After installation, a malfunctioning light source should be replaced easily, without drilling or milling. The light source’s sensitivity for pollution from its surroundings must be minimal; the absence of sharp joints and edges prevents the gathering of dirt and dust and increases the self-cleaning effect of rain or tire traffic. • Supply and mounting of light source(s), electronic parts, and housings as separate components ease replacement when a failure occurs, reduces waste, and provides the potential to reuse parts that have a longer lifespan than the road surface. With respect to light color, the Dutch require the color of the IPM system marker to be the same as that of the existing (passive) marking. The desired light intensity depends on where the IPM system is used and is influenced by the maximum road user perception distance (with an assumed preview of 15 s) and the presence and intensity of the surrounding lighting. The Dutch recommend the following light intensities based on surrounding lighting conditions: • 500 millicandelas in complete darkness or with low dif- fused lighting; • 1000 millicandelas when background lighting is present; and • 2000 millicandelas when combined with or near conven- tional lighting. The light yield from an IPM system can be relatively low. Enough light must be emitted to make the marker visible at a great distance, but not so much light that the driver is unable to see other road users or obstacles in front of him or her. In situations where surrounding lighting is present, a higher light intensity must be used than in situations where it is almost completely dark. Aperture angle, defined as the angle indicating the width of a light beam, is an important factor in IPM system appli- cations along horizontal curves. As the radius tightens, the road user’s view through the curve becomes smaller, making it necessary to place more markers in a certain section of the road so that the path of the curve becomes recognizable. If the radius is small (less than 1,968 ft for one-lane roadways or greater than 3,281 ft for two-lane roadways), it is also neces- sary to direct the markers at the oncoming traffic (an alternative is to increase the aperture angle, but this compromises the light yield). The Dutch recommend using a 12-degree hori- zontal aperture angle and a 10-degree (minimum 8-degree, maximum 12-degree) vertical aperture angle for optimal vis- ibility over the complete IPM system-equipped curve section. When placing the IPM system markers in the pavement, the Dutch define two maximum height requirement conditions. The maximum height over the road surface is 0.20 in. for hori- zontal curves with mixed traffic (i.e., cars, mopeds, and motor- cycles) and 0.39 in. for horizontal curves with car traffic only. When positioning IPM systems on the pavement surface, markers are always installed along the outside edgeline of one-way roadways, regardless of the number of lanes. For two-way roadways, the markers are placed along the center- line of the roadway. The Dutch recommend placing the IPM system markers directly on (or in) the existing passive mark- ing or immediately beside it to maintain the delineation of the roadway (Recommendation . . . 2005). The marker spacing is the most important variable factor when implementing an IPM system. The desirable distance between markers is affected by the visibility of the locale, the radius of the roadway, and the maximum travel speed. On a straight road section the maximum speed limit is the only factor that determines the distance between the markers. The Dutch recommend various speed-based marker distances ranging from approximately 82 ft at 20 mph to approximately 325 ft at 75 mph. To determine appropriate marker spacing along a hori- zontal curve, the Dutch provide the following relationship: where: KL is the marker distance in radians, R is the radius of the curve measured to the centerline of the lane curve in meters, B is the width of the lane in meters, KL R BN R B S R = +⎡ ⎣⎢ ⎤ ⎦⎥ − − + ( . ) arccos ( . ) ( . 0 5 0 5 0 5 * * * * B) ⎡ ⎣⎢ ⎤ ⎦⎥

S is the distance between the edgeline and the obstacles on the inside curve in meters, and N is the required minimum number of markers visible to the road user; a minimum N of 5 is recommended. Bringing all of these principles together, the Dutch provide a detailed example application for a horizontal curve section. The reader is referred to the original citation for details (Rec- ommendation . . . 2005). Finally, the Dutch developed a multistep decision tree to support implementation decisions related to IPM systems. In summary, this multistep process • Distinguishes between roads that are already lit and unlit, • Investigates the potential to remove or omit conven- tional lighting if IPM systems are installed, • Investigates the potential to reduce the energy consump- tion and environmental interference if IPM systems are installed, • Determines the cost-effectiveness of the IPM system and determines acceptability, and • Investigates the potential to “switch off” conventional lighting under favorable traffic and weather circum- stances (i.e., as a cost-effective alternative to IPM sys- tem installation). HISTORICAL APPLICATIONS As mentioned previously, IPM systems were first used to provide path guidance for airport runways and taxiways and later emerged as an enhanced warning tool for pedestrian crosswalks. Although the technology characteristics and sub- sequent costs of IPM systems have changed significantly since these earlier applications, a review of experiences re- lated to IPM system installation and maintenance may provide valuable precautionary information for new system installa- tions. In addition, a review of observed IPM system effective- ness may support decision making for related applications. For instance, it might be inferred that intersection stop bars equipped with IPM systems may experience similar benefits related to reduced vehicle approach speeds and increased ve- hicle compliance as those observed for pedestrian crosswalks. Airport Runways and Taxiways Published information related to the use of IPM systems on airport runways and taxiways focused predominantly on the evolution of technology from tungsten bulbs, which were expensive to install and maintain, to LED light sources, which were found to be less expensive to install and operate. A few studies were uncovered that focused on the performance of IPM systems in airport applications. As early as 1978, Douglas investigated the use of green lights installed in the runway surface on the extended taxiway 16 centerline marking for lighting both high-speed and low-speed exits. This method had not yet been adopted in the United States because of concern over the possibility of mistaking a low-speed exit for a high-speed exit. To address these concerns, the author recommended: (1) modifying the type L-829 signs located at exits from the runway to increase their conspicuous- ness, (2) improved shielding to taxiway edge lights, (3) use of asymmetric instead of symmetric lenses on straight stretches, (4) dimming of taxiway edge lights to reduce the “sea-of-blue” effect, and (5) use of high-efficiency retroreflective paint to mark the turn-offs to the exit taxiway to improve nighttime guidance. A system of pulsating blue lights at the entrance to the exit taxiway throat also showed promise (Douglas 1978). More than 15 years later, Katz and Paprocki (1994) devel- oped and tested the performance of a prototype enhanced vi- sual taxiway identification system, consisting of a segment of green lights imbedded within the conventional runway cen- terline lighting system at the FAA William J. Hughes Tech- nical Center. Results of the effort indicated that the system may be expected to provide enhanced and effective identifi- cation of taxiway exit locations at minimal cost. At the same facility, Gallagher (2001) evaluated the use of LED light strips with a focus on pilot and lighting personnel perceptions. The LED light strips augmented painted surface markings, which were still deemed necessary for daytime and inclement weather conditions. Gallagher found that all but one participant rated the LED light strips as a valuable augmentation to the painted surface markings. Most recently, Patterson (2004) reported specific opera- tional problems attributable the use of runway guard lights installed at hold lines at the Chicago O’Hare International Airport. In this application, a series of alternate flashing, yel- low, unidirectional, in-pavement lighting fixtures are equally spaced along a runway holding position. These markings are intended to be visible only to aircraft approaching the hold position from the taxiway. In some instances, however, pilots have reported that the lights are visible from the opposite side of the fixtures (i.e., to aircraft exiting the runway) resulting in false guidance information to the pilots. No information was provided regarding how this issue was resolved. These limited reported experiences suggest important find- ings related to directional illumination, luminous intensity, and supplemental use of surface markings. Installation, main- tenance, and cost information was not uncovered (except for the earliest types of IPM systems). The transferability of this latter information is likely more limited given differences in vehicles and vehicle operating characteristics between road- way and airport environments. Pedestrian Crosswalks Commonly referred to as “flashing crosswalks,” IPM sys- tems for pedestrian crosswalk applications include the basic

17 components of: (1) IPMs, (2) an AC or solar power source, and (3) a manual push-button or passive activation system (see Figure 4). Over time, and with expanded IPM system implementation, various installation, operation, and mainte- nance challenges have been identified. As noted previously, some passive activation systems, par- ticularly those relying on microwave detectors, have experi- enced higher rates of false positives and misses. A passive activation bollard system in San Jose, California, malfunc- tioned as a result of vandalism (Malek 2001). Of more con- cern, citizens in Santa Monica, California, are reporting a false sense of pedestrian security, which, when combined with a high rate of system malfunction, has purportedly led to multiple pedestrian–vehicles crashes and one resulting death (Ericksen 2007). A greater variety of maintenance challenges have been identified. Specific to halogen light sources, halogen lamps reportedly experienced frequent water condensation and bro- ken filaments. Applying more generally to all IPM system marker types, recessed markers require frequent cleaning to eliminate dirt and debris from the lens surface. In-pavement markers that protrude above the ground have experienced damage by street cleaners and snowplows (in at least one application, the damage did not prevent the light from re- maining operational) (Malek 2001). Manufacturers moved to aluminum or stainless steel housing materials to address this issue. Activities such as street repair or resurfacing require the IPM system to be removed and reinstalled or lost. Challenges related to system settlement have also been reported; over time and under traffic load, the markers are pressed further into the pavement, eventually damaging the power supply conduit and causing system failure (Ericksen 2007). City officials in Santa Monica suggest that the use of portland concrete cement instead of asphalt concrete pave- ment would address this challenge (Ericksen 2007). City officials in Santa Monica, California, also report significant delays in receiving system parts (e.g., replace- ment lights) when system failures do occur. These reported delays differ between independent suppliers. One supplier at- tributed delays to the discontinuance of the product, whereas another attributed delays to pending product improvements that would result in a brighter, and more robust, marker and a backlog of replacement orders resulting from a minor engi- neering design change (Ericksen 2007). For pedestrian crosswalk applications, IPM system costs have ranged from $5,000 to $100,000 per application. Factors affecting cost include the length and layout of the application and the subsequent number of markers required; specific fea- tures of the IPM system (e.g., unidirectional or bidirectional dis- plays and operational modes); the availability and nature (e.g., solar) of power at the site; the condition of the pavement and any remedial actions required before IPM system installation; FIGURE 4 “Smart crosswalk system” (Courtesy: LightGuard Systems, Inc.). Measure Author Comments Huang et al. (1999) Actuated flashing provides an advantage over continuous flashing Malek (2001) More effective than overhead beacon, especially at night Boyce and Van Derlofske (2002) Enhanced Driver Awareness Whitlock and Weinburger (1998) Particularly beneficial during adverse weather Increased Vehicle Yielding Huang et al. (1999) Huang et al. (1999) Boyce and Van Derlofske (2002) Reduced Vehicle Speeds Prevedouros (2000) 17.8% to 16.2% reduction in maximum speed 27.2% to 25.2% reduction in average speed 16.3% to 14.0% reduction in 85th percentile speed Huang et al. (1999) Reduced Vehicle/ Pedestrian Conflicts Boyce and Van Derlofske (2002) Reduced number of vehicles entering crosswalk while pedestrian waiting Lower Pedestrian Wait Times Prevedouros (2000) 50.5% reduction (26.7 s to 13.2 s) TABLE 2 BENEFITS OF IN-PAVEMENT WARNING LIGHTS AT CROSSWALKS

and traffic control requirements. A broader range of costs is anticipated for the emerging IPM system applications intended to enhance guidance, regulation, and illumination. Regarding the effectiveness of IPM systems in pedestrian crosswalk applications, the results are generally favorable al- though the quality of prior study designs has been criticized. Few studies have directly measured the effect of IPM systems on pedestrian crosswalk safety; the infrequency of crashes and the time duration required to achieve an adequate sample preclude direct measurement. Instead, prior studies have con- sidered various surrogate safety measures including enhanced driver awareness, increased vehicle yielding, reduced vehicle speeds, or reduced vehicle–pedestrian conflicts (defined as a 18 vehicle and a pedestrian in a crosswalk at the same time). A single study was identified that considered the effect of IPM systems on pedestrian crosswalk operation (i.e., in reducing pedestrian wait times). Table 2 summarizes previous studies investigating the effectiveness of IPM systems at pedestrian crosswalks. Despite individual study limitations, a positive trend in IPM system effectiveness in enhancing pedestrian crosswalk safety and operation can be observed. In-pavement marker systems have generally been shown to increase vehicle driver awareness, increase vehicle yielding, reduce vehicle approach speeds, reduce vehicle–pedestrian conflicts, and reduce pedes- trian wait times in this type of application.

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TRB's National Cooperative Highway Research Program (NCHRP) Synthesis 380: Applications of Illuminated, Active, In-Pavement Marker Systems (IPMs) explores the state of IPM technology, experiences with IPM applications, and potential IPM research needs.

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