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APPLICATIONS OF ILLUMINATED, ACTIVE, IN-PAVEMENT MARKER SYSTEMS SUMMARY Various types of illuminated, active, in-pavement marker (IPM) systems are emerging that offer a range of designs and functional features intended to warn, guide, regulate, or provide illumination for road users. Although the number and breadth of IPM system applications has increased in recent years, little documentation has been created about the effectiveness of these systems in enhancing roadway safety, operations, or aesthetics. Further, little guid- ance is available to support proper planning, installation, operation, and maintenance of the systems. Based on information obtained through a review of published literature, a formal survey of transportation practitioners, and an informal survey of IPM system vendors and users, this synthesis report documents the current state of knowledge related to IPM system use and effectiveness. More specifically, this report documents: (1) the state of IPM technology, including technology characteristics and standards and guidelines for use; (2) notable expe- riences from historical IPM system applications; and (3) detailed experiences from more recent IPM system applications, including system and facility characteristics, operation modes, installation and construction methods, maintenance requirements, system costs, and perceived and measured effectiveness. Assimilated in this synthesis report, this information will help to accelerate successful applications and focus future research of IPM systems. The survey questionnaire was distributed to state traffic engineers from all 50 states, the District of Columbia, and Puerto Rico; traffic or public works engineers from the top 200 metropolitan statistical areas of the United States, and to the ITE Traffic Engineering Council Listserve, a total of 865 contacts. Sixty-two of the 865 completed the survey (a 7.2% response rate). Key findings related to IPM system applications, technology characteristics, installation and construction methods, operation modes, maintenance requirements, costs, and perceived and measured effectiveness are summarized here. Given the relative novelty of IPM system use on public roadways, little direction in the form of standards or guidelines is available for practitioners to support proper installation, operation, and maintenance of the systems. At the national level, the 2004 Manual on Uniform Traffic Control Devices (MUTCD) provides significant general guidance related to traffic control devices (e.g., signs, markings, and highway traffic signals), but contains few explicit standards, guidance, or options for IPM system use, and focuses exclusively on pedestrian crosswalk applications. Historically, IPM system use has been limited to airport runway/taxiway or pedestrian crosswalk applications. More recently, IPM systems have been used to enhance: (1) warn- ing through school and construction zones, at highway/rail crossings, at horizontal curves, and during adverse weather; (2) guidance through multiple-turn lanes, at merge locations, and through tunnels; (3) regulation at intersection stop bars and where left turns are prohib- ited; and (4) illumination at vehicle/truck inspection points and environmentally sensitive areas.
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2 IPM systems generally comprise an illumination source surrounded by a protective hous- ing and lens, a power source, and a system controller in a protective enclosure. None of the IPM systems observed provided automatic notification of system failure; instead, failures were detected through remote surveillance, on-site inspection, or public reports. Should this capability be added to IPM systems, the design and use of this feature could be guided by related Intelligent Transportation Systems standards. 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 limitations preventing widespread applica- tions. Flexibility in color and luminous intensity, low power consumption, and extended useful life, have caused LED to emerge as the favored light source for IPM systems. For the IPM systems observed, several issues related to the luminous intensity of the light source were identified. Compromised luminous intensity was reported during daylight oper- ation as compared with nighttime operation at several sites. In addition, luminous intensity was reportedly lower for IPM systems relying on solar technology, as opposed to hardwired or inductive systems. Although not confirmed through measurement, a decrease in luminous intensity was also reported over time. Last, an increased capability in color features (i.e., utilizing more than one color per marker) reduces the number of LEDs illuminated simulta- neously and, hence, reduces the luminous intensity of the marker. Housing materials commonly have been made of plastic, although newer markers are more frequently made of aluminum or stainless steel for improved durability. Lens materials com- monly include polycarbonate or boron and glass. Some vendors include a passive retro- reflective lens (i.e., a prismatic surface that reflects external light sources) in addition to ac- tive illumination to provide fail-safe operation should the IPM system become disabled. IPM systems can derive power to operate through hardwired electrical connections, induc- tive wireless connections, or through solar technology. To date, hardwired electrical connec- tions and inductive wireless connections have outperformed (e.g., through higher luminous intensity and more consistent operation) individual IPM units relying on solar technology. Benefits to solar-powered IPM systems, however, include the ease and flexibility of installa- tion, particularly for remote areas. Continued advancements in solar technology may make this a more viable IPM system power source in the future. The IPM system controllers are typically housed in a protective cabinet or enclosure. For lightning protection, a ground box with a copper ground rod is typically located near the cabinet or enclosure. In electrical-storm-prone areas, lightning protection for IPM systems is especially important. Each IPM system vendor provides more detailed installation instructions tailored to their specific product. For placement of the electrical cable and/or conduit, a common method requires saw- cutting a 3/8 in. to 1/2 in. groove in the pavement for cable-only installations (a larger cut is required to accommodate a larger diameter conduit). The electrical conduit is placed in the groove and typically covered with epoxy. For inductive IPM systems, both the conduit and node assembly are placed in the groove and sealed with epoxy. It is impor- tant to provide enough depth to the saw cut to adequately recess and protect the electrical cable and/or conduit. Individually solar-powered IPM units do not require this installa- tion step. Several of the observed IPM systems noted power supply issues following installation. A few of these instances were attributable to a manufacturer defect. Power supply issues were
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3 more commonly attributed, however, to a lack of familiarity with installation procedures by the contractor or poor quality control during installation (e.g., water penetration). Markers can be recessed in the pavement through coring or milling methods or affixed directly to the pavement surface. Recessed markers are less prone to "pop-offs" but require additional effort during the installation process. In cold regions, where snowplowing is fre- quent during the winter months, use of recessed markers is necessary. Also, the performance of marker adhesives, particularly in unusually cold or hot temperatures, can have a signifi- cant effect on pop-off frequency. In most instances, manufacturers have been able to signif- icantly reduce the occurrence of pop-offs through the use of alternate adhesive; however, this action generally only follows a period of poor IPM system performance. As observed in this synthesis effort, markers can also be placed on other roadway features, most commonly including concrete barriers and sign posts. IPM systems that utilized barrier- or post-mounted markers experienced significantly fewer pop-offs. Based on pedestrian crosswalk experience, a high frequency of system failures in a single jurisdiction was attributable to marker settlement and subsequent power supply issues in asphalt concrete pavements. This issue was purportedly avoidable if the IPM systems were installed in portland cement concrete pavement. Although the IPM systems observed for this synthesis included a range of pavement materials, no additional information was uncovered that described the comparative performance of IPM systems that were installed in either port- land cement concrete or asphalt concrete pavements. Additionally, no consistent standard for IPM system marker spacing was observed within similar applications. Between applications, marker spacing was generally observed to in- crease as traffic speeds increased. Activation of IPM systems relies on either manual methods, where the system is acti- vated directly by the road user (e.g., a push-button system), or passive methods, where the system is activated automatically through some type of sensor input. Passive activation can be provided through in-ground sensors, motion sensors, visual image video detection sys- tems, in-pavement loop detectors, integration with traffic control devices, and road-weather information systems. Manual activation methods are typically lowest cost, but require action from the road user to be effective. Passive activation methods are more discrete, but may suffer a high frequency of false positives and misses, particularly when using microwave technology. Additional IPM system activation methods observed included timer-based activation (in the case of a school zone) and ambient light-sensitive activation through the use of photo- electric cells to detect dusk (for activation) and dawn (for deactivation). The nature of IPM system activation depends somewhat on the intended function of the system and the characteristics of the environment in which it is placed. Systems that are intended to guide road users are often operated continuously, particularly those in high-traffic environments. Conversely, IPM systems that are intended to warn, regulate, or provide illumi- nation are more commonly operated intermittently, in response to a detected hazard or regu- latory action, or to minimize environmental effects and energy consumption. Depending on the manufacturer, IPM systems offer a range of features that have the poten- tial to enhance roadway operations. Marker color changes can be used to indicate regulatory action required by the road user (e.g., markers show red illumination when vehicles are required to stop). Varying flash rates (including steady burn) can indicate the level of hazard. In addi- tion, "chase" sequences can direct the road user to reduce or increase speeds, or provide direc- tional guidance through an intersection turning movement.
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4 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 consistently (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 (e.g., to indicate wrong way travel). Use of multiple colors in the IPM system marker reduces the luminous intensity for any single illu- mination (i.e., a marker that contains 10 total LEDs would illuminate 5 LEDs of one color followed by 5 LEDs of another color). In the IPM systems observed, use of white, amber, and red markers were noted, most com- monly as single-color configurations, although some of the markers provided dual-color illu- mination to coincide with the red and amber traffic signal indications. IPM systems can be operated in a steady-burn state or in a flashing mode, consistently or intermittently. The flashing mode may be triggered by a detected hazard (e.g., when upstream speed sensors detect a vehicle traveling too fast for a curve or when road-weather informa- tion systems detects fog conditions) and may, depending on the manufacturer, provide an adjustable increasing flash rate consistent with increasing danger (as long as the flash rate remains within an acceptable range). At all other times, the IPM system may show steady or no illumination. 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 consistent and appropriate speeds 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 applications include horizontal curves, tunnels, merge areas, and construction work zones. The majority of IPM systems observed operated in steady-burn state once activated; flash and chase features were more common in systems intended to provide warning (in one case, chase sequences were used to provide guidance through multiple-turn lane maneuvers). Specific to halogen light sources, halogen lamps reportedly experienced frequent water condensation and broken filaments. Applying more generally to all IPM system marker types, frequent light source failures were consistently reported over all applications. Failures were generally attributed to environmental factors (e.g., water, dirt, and debris buildup) or traffic impacts. For markers located in the tire path of vehicles and particularly heavy vehicles, light source failure was particularly problematic. This condition is inherent in the design of IPM systems for multiple-turn lanes; vehicles traveling through the intersection are required to drive over a portion of the multiple-turn lane delineation. Ongoing light source failures can become costly if not included under a manufacturer's warranty. Annual maintenance costs for one IPM system were estimated to be $15,000, comprised largely of LED failure replace- ment costs. One jurisdiction reported significant delays in delivery of replacement parts. IPMs that protrude above the ground have also experienced damage by street cleaners and snowplows. System manufacturers have moved to aluminum or stainless steel housing mate- rials typically recessed into the pavement to address this issue. Recessed markers that also help to minimize damage from street cleaners and snowplows require frequent cleaning to eliminate dirt and debris from the lens surface. This requirement was frequently noted for the IPM systems observed in this synthesis effort. In some cases, the IPM system required cleaning (e.g., power washing) as frequently as once per month. Barrier- or post-mounted IPM sys- tems do not require this same level of maintenance. It was also noted that activities such as street repair or resurfacing require the IPM system to be removed and reinstalled or lost. This is not unique to IPM system applications but
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5 challenges the longevity of any type of roadway instrumentation. Again, barrier- or post- mounted IPM systems are less likely to be affected by roadway repair or resurfacing activities. IPM system costs can range significantly, anywhere from $5,000 up to $100,000. Factors affecting cost include the length and layout of the application and the subsequent number of markers required, specific features of the IPM system (e.g., unidirectional or bidirectional displays and operational modes), the availability and nature of power at the site (e.g., solar), the condition of the pavement and any remedial actions required before IPM system installa- tion, and traffic control requirements. In general, implementing agencies do not consider IPM systems to be a "low-cost" alternative to traditional traffic control devices and suggest that use be limited to critical locations. Opportunities for federal funding to support IPM system implementation may be constrained by proprietary issues (i.e., FHWA typically requires system bids from three or more vendors; patented products may not be approved for wide- spread implementation). Few formal evaluations have been performed to determine the effectiveness of IPM systems in enhancing roadway safety, operations, or aesthetics. Pedestrian crosswalk appli- cations have been most frequently studied; IPM systems have generally been shown to increase vehicle driver awareness, increase vehicle yielding, reduce vehicle approach speeds, reduce vehicle and pedestrian conflicts, and reduce pedestrian wait times. Considering broader applications of IPM systems, additional studies have generally shown a reduction in vehicle speeds, improved lane-tracking, increased road user awareness, and high public acceptance. More recent studies have been conducted in response to FHWA's requirements for experimental status. Early results reported from these studies show promise but are generally based on limited data and, as such, cannot be considered conclusive. Implementing agencies provided significant anecdotal information through this synthesis effort attesting to the effectiveness of IPM systems in enhancing various aspects of roadway safety, operations, or aesthetics depending on the nature of the application. A high overall degree of IPM system satisfaction was reported despite any installation or maintenance chal- lenges encountered. Furthermore, implementing agencies noted a high level of public support for and acceptance of IPM systems. Based on the information gathered through this synthesis effort, illuminated, active, IPM systems show potential for: (1) enhancing warning through school and construction zones, at highwayrail crossings, at horizontal curves, and during adverse weather; (2) enhancing guid- ance through multiple-turn lanes, at merge locations, and through tunnels; (3) enhancing reg- ulation at intersection stop bars and where left turns are prohibited; and (4) enhancing illumination at vehicle and truck inspection points and environmentally sensitive areas. Direct benefits of IPM systems in each of these applications cannot be quantified conclusively because few acceptable evaluations of recent IPM system applications have been performed, and because inadequate installation, operation, and maintenance guidance is likely confound- ing system performance. As such, recommendations to accelerate successful applications of IPM systems relate to focused research, and evaluation and development of related standards and guidelines.