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39 CHAPTER FOUR CONCLUSIONS Various types of illuminated, active, in-pavement marker Applications (IPM) systems are emerging that offer a range of designs and functional features intended to warn, guide, regulate, or pro- Historically, IPM system use was limited to airport runway/ vide illumination for road users. Although the number and taxiway or pedestrian crosswalk applications. More recently, breadth of IPM system applications has increased in recent IPM systems have been used to enhance: years, little has been documented about the effectiveness of these systems in enhancing roadway safety, operations, or · Warning through school and construction zones, at aesthetics. Furthermore, little guidance is available to sup- highwayrail crossings, at horizontal curves, and during port proper planning, installation, operation, and maintenance adverse weather; of the systems. · Guidance through multiple-turn lanes, at merge locations, and through tunnels; This synthesis report documents the current state of knowl- · Regulation at intersection stop bars and where left turns edge related to IPM system use and effectiveness. More are prohibited; and specifically, this report documents: (1) the state of IPM tech- · Illumination at vehicle and truck inspection points and nology, including technology characteristics and standards environmentally sensitive areas. and guidelines for use; (2) notable experiences from histor- ical IPM system applications; and (3) detailed experiences Technology Characteristics from recent IPM system applications, including system and facility characteristics, operation modes, installation and con- Generally, IPM systems consist of an illumination source struction methods, maintenance requirements, system costs, surrounded by a protective housing and lens, a power source, and perceived and measured effectiveness. Assimilated in and a system controller in a protective enclosure. The design this synthesis report, this information will help to accelerate and features of the various components may vary significantly successful applications and focus future research of IPM depending on the type of application. None of the IPM systems systems. observed provided automatic notification of system failure; instead, failures were detected through remote surveillance, This chapter provides a summary of key findings and pre- on-site inspection, or public reports. Should this capability be sents applicable suggestions based on the information obtained added to IPM systems, the design and use of this feature in this synthesis effort. could be guided by related Intelligent Transportation Systems (ITS) standards. SUMMARY OF KEY FINDINGS Illumination Source Key findings related to IPM system applications, technology characteristics, installation and construction methods, oper- Both incandescent/halogen lamps and light-emitting diodes ation modes, maintenance requirements, costs, and perceived (LED) have been commonly used as light sources in IPM and measured effectiveness are summarized here. Given systems. Laser and electroluminescence technology has also the relative novelty of IPM system use on public roadways, been considered for use; however, each has respective limi- little direction in the form of standards or guidelines is avail- tations preventing widespread applications. Flexibility in color able to support proper installation, operation, and mainte- and luminous intensity, low power consumption, and extended nance of the systems. At the federal level, the Manual on useful life, has resulted in LED emerging as the favored light Uniform Traffic Control Devices (MUTCD) (2004) provides source for IPM systems. significant general guidance related to traffic control devices (e.g., signs, markings, and highway traffic signals), but con- For the IPM systems observed, several issues related to tains few explicit standards, guidance, or options for IPM the luminous intensity of the light source were identified. Com- system use and focuses exclusively on pedestrian crosswalk promised luminous intensity was reported during daylight applications. operation as compared with nighttime operation at several
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40 sites. In addition, luminous intensity was reportedly lower for the saw cut to adequately recess and protect the electrical IPM systems relying on solar technology, as opposed to hard- cable and/or conduit. Individual unit solar-powered IPM sys- wired or inductive systems. Although not confirmed through tems do not require this installation step. measurement, a decrease in luminous intensity was also re- ported over time. Last, an increased capability in color features Several of the observed IPM systems noted power supply (i.e., utilizing more than one color per marker) reduces the issues following installation. A few of these instances were number of LEDs illuminated simultaneously and hence re- attributable to a manufacturer defect. Power supply issues duces the luminous intensity of the marker. were more commonly attributed, however, to a lack of famil- iarity with installation procedures by the contractor or poor quality control during installation (e.g., water penetration). Housing and Lens Markers can be recessed in the pavement through coring Housing materials, typically measuring no more than 6 in. or milling methods or affixed directly to the pavement surface. along the largest dimension, have commonly been made of Recessed markers are less prone to "pop-offs" but require plastic, although newer markers are more frequently made of additional effort during the installation process. In cold re- aluminum or stainless steel for improved durability. Lens gions, where snowplowing is frequent, use of recessed mark- materials commonly include polycarbonate or boron/glass. ers is necessary. Also, the performance of marker adhesives, Some vendors include a passive retroreflective lens (i.e., a pris- particularly in unusually cold or hot temperatures, can have matic surface that reflects external light sources) in addition a significant effect on pop-off frequency. In most instances, to active illumination to provide fail-safe operation should manufacturers have been able to significantly reduce the the IPM system lose power. occurrence of pop-offs through the use of alternate adhesive; however, this action generally only follows a period of poor Power Source IPM system performance. IPM systems can derive power to operate through hardwired As observed in this synthesis effort, markers can also be electrical connections, inductive wireless connections, or solar placed on concrete barriers, sign posts, etc. IPM systems that technology. To date, hardwired electrical connections and in- use barrier- or post-mounted markers experienced signifi- ductive wireless connections have outperformed (i.e., higher cantly fewer pop-offs. luminous intensity, more consistent operation) IPM systems relying on solar technology. Benefits to solar-powered IPM Based on pedestrian crosswalk experience, a high frequency systems include the ease and flexibility of installation, par- of system failures in a single jurisdiction was attributable ticularly for remote areas. Continued advancements in solar to marker settlement and subsequent power supply issues in technology may make this a more viable IPM system power asphalt concrete pavements. This issue was purportedly source in the future. avoidable if the IPM systems were installed in portland con- crete cement pavement. Although the IPM systems observed in this synthesis effort included a range of pavement materi- System Controller and Enclosures als, no additional information was uncovered that described the comparative performance of IPM systems that were in- The IPM system controllers are typically housed in a protec- stalled in either portland concrete cement or asphalt concrete tive cabinet or enclosure. For lightning protection, a ground pavements. box with copper ground rod is typically located near the cabinet/enclosure. In electrical storm-prone areas, lightning Additionally, no consistent standard for IPM system marker protection for IPM systems is especially important. spacing was observed within similar applications. Between applications, marker spacing was generally observed to in- Installation and Construction Methods crease as traffic speeds increased. Each IPM system vendor provides more detailed installation Operation Modes instructions tailored to its specific product. System Activation For placement of the electrical cable and/or conduit, a common method requires saw-cutting a 3/8 in. to 1/2 in. Activation of IPM systems relies on either manual methods, groove in the pavement for cable-only installations (a larger where the system is activated directly by the road user (e.g., cut is required to accommodate a larger-diameter conduit). a push-button system) or passive methods, where the system The electrical conduit is placed in the saw cut and typically is activated automatically through some type of sensor input. covered with epoxy. For inductive IPM systems, both the Passive activation can be provided through in-ground sen- conduit and node assembly are placed in the saw cut and sors, motion sensors, visual image video detection systems, sealed with epoxy. It is important to provide enough depth to in-pavement loop detectors, integration with traffic control
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41 devices, and road-weather information systems. Manual acti- acceptable range). All other times, the IPM system may show vation methods are typically lowest in cost, but require action steady or no illumination. from the road user to be effective. Passive activation meth- ods are more discrete, but may suffer a high frequency of More sophisticated IPM systems offer forward or reverse false positives and misses, particularly when using microwave chase sequencing (i.e., adjacent markers are sequentially il- technology. luminated giving the effect of moving light along the path). This feature is intended to improve speed-related roadway Additional IPM system activation methods observed in operations by pacing traffic at consistent and appropriate this synthesis effort included timer-based activation (in the speeds for conditions. Chase sequencing has been used to case of a school zone) and ambient light-sensitive activation maintain or reduce vehicle speeds in fog-prone areas and to through the use of photoelectric cells to detect dusk (for acti- reduce vehicle speeds on exit ramps. Other potential applica- vation) and dawn (for deactivation). tions include horizontal curves, tunnels, merge areas, or con- struction work zones. The nature of IPM system activation depends somewhat on the intended function of the system and the characteris- In the IPM systems observed, use of white, amber, and red tics of the environment in which it is placed. Systems that markers were noted, most commonly as single-color config- are intended to guide road users are often operated contin- urations, although some of the markers provided dual-color uously, particularly those in high-traffic environments. Con- illumination to coincide with the red and amber traffic signal versely, IPM systems that are intended to warn, regulate, indications. The majority of IPM systems observed operated in or provide illumination are more commonly operated in- steady-burn state once activated; flash and chase features were termittently, in response to a detected hazard or regulatory more common in systems intended to provide warning (in one action, or to minimize environmental effects and energy case, chase sequences were used to provide guidance through consumption. multiple-turn lane maneuvers). Modes of Operation Maintenance Requirements Depending on the manufacturer, IPM systems offer a range Specific to halogen light sources, halogen lamps reportedly of features that have the potential to enhance roadway oper- experienced frequent water condensation and broken filaments. ations. Marker color changes can be used to indicate regula- Applying more generally to all IPM system marker types, tory action required by the road user (e.g., markers show red frequent light source failures were consistently reported over illumination when vehicles are required to stop). Varying flash all applications. Failures were generally attributed to environ- rates (including steady burn) can indicate the level of hazard. mental factors (e.g., water, dirt, and debris build-up) or traffic Also, "chase" sequences can direct the road user to reduce or impacts. For markers located in the tire path of vehicles and increase speeds. particularly heavy vehicles, light source failure was partic- ularly problematic. This condition is inherent in the design Common IPM system marker colors include white, amber, of IPM systems for multiple-turn lanes; vehicles traveling red, green, and blue. Using LED illumination technology, through the intersection are required to drive over a portion IPM system markers can illuminate the same color in all of the multiple-turn lane delineation. Ongoing light source directions, can alternate colors consistently (i.e., all markers failures can become costly if not included under a manu- show red illumination when vehicles are required to stop, but facturer's warranty. Annual maintenance costs for one IPM return to green or white when vehicles are permitted to travel), system were estimated to be $15,000, comprised largely of or can illuminate two different colors by direction (i.e., to in- LED failure replacement costs. One jurisdiction reported dicate wrong way travel). Use of multiple colors in the IPM significant delays in delivery of replacement parts. system marker reduces the luminous intensity for any single illumination (i.e., a marker that contains 10 total LEDs would System markers that protrude above the ground have also illuminate 5 LEDs of one color followed by 5 LEDs of an- experienced damage by street cleaners and snowplows. System other color). manufacturers have moved to aluminum or stainless steel housing materials typically recessed into the pavement to ad- IPM systems can be operated in a steady-burn state or in dress this issue. Recessed markers that also help to minimize a flashing mode, consistently or intermittently. The flashing damage from street cleaners and snowplows require frequent mode may be triggered by a detected hazard (e.g., when up- cleaning to eliminate dirt and debris from the lens surface. stream speed sensors detect a vehicle traveling too fast for a This requirement was frequently noted for the IPM systems curve or when a road-weather information system detects fog observed in this synthesis effort. In some cases, the IPM conditions) and may, depending on the manufacturer, pro- system required cleaning (e.g., power washing) as frequently vide an adjustable increasing flash rate consistent with in- as once per month. Barrier- or post-mounted IPM systems do creasing danger (as long as the flash rate remains within an not require this same level of maintenance.