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

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

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

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