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

Chapter: Chapter Four - Conclusions

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Suggested Citation:"Chapter Four - Conclusions." 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 Four - Conclusions." 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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Page 39
Page 40
Suggested Citation:"Chapter Four - Conclusions." 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.
×
Page 40
Page 41
Suggested Citation:"Chapter Four - Conclusions." 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.
×
Page 41
Page 42
Suggested Citation:"Chapter Four - Conclusions." 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.
×
Page 42

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39 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 pro- vide illumination for road users. Although the number and breadth of IPM system applications has increased in recent years, little has been documented about the effectiveness of these systems in enhancing roadway safety, operations, or aesthetics. Furthermore, little guidance is available to sup- port proper planning, installation, operation, and maintenance of the systems. This synthesis report documents the current state of knowl- edge related to IPM system use and effectiveness. More specifically, this report documents: (1) the state of IPM tech- nology, including technology characteristics and standards and guidelines for use; (2) notable experiences from histor- ical IPM system applications; and (3) detailed experiences from recent IPM system applications, including system and facility characteristics, operation modes, installation and con- struction 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. This chapter provides a summary of key findings and pre- sents applicable suggestions based on the information obtained in this synthesis effort. SUMMARY OF KEY FINDINGS Key findings related to IPM system applications, technology characteristics, installation and construction methods, oper- ation 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 avail- able to support proper installation, operation, and mainte- nance of the systems. At the federal level, the Manual on Uniform Traffic Control Devices (MUTCD) (2004) provides significant general guidance related to traffic control devices (e.g., signs, markings, and highway traffic signals), but con- tains few explicit standards, guidance, or options for IPM system use and focuses exclusively on pedestrian crosswalk applications. Applications Historically, IPM system use was limited to airport runway/ taxiway or pedestrian crosswalk applications. More recently, IPM systems have been used to enhance: • Warning through school and construction zones, at highway–rail crossings, at horizontal curves, and during adverse weather; • Guidance through multiple-turn lanes, at merge locations, and through tunnels; • Regulation at intersection stop bars and where left turns are prohibited; and • Illumination at vehicle and truck inspection points and environmentally sensitive areas. Technology Characteristics Generally, IPM systems consist of an illumination source surrounded 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 significantly depending on the type of application. 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 (ITS) standards. 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 applications. Flexibility in color and luminous intensity, low power consumption, and extended useful life, has resulted in LED emerging 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. Com- promised luminous intensity was reported during daylight operation as compared with nighttime operation at several CHAPTER FOUR CONCLUSIONS

sites. In addition, luminous intensity was reportedly lower for IPM systems relying on solar technology, as opposed to hard- wired or inductive systems. Although not confirmed through measurement, a decrease in luminous intensity was also re- ported over time. Last, an increased capability in color features (i.e., utilizing more than one color per marker) reduces the number of LEDs illuminated simultaneously and hence re- duces the luminous intensity of the marker. Housing and Lens Housing materials, typically measuring no more than 6 in. along the largest dimension, have commonly been made of plastic, although newer markers are more frequently made of aluminum or stainless steel for improved durability. Lens materials commonly include polycarbonate or boron/glass. Some vendors include a passive retroreflective lens (i.e., a pris- matic surface that reflects external light sources) in addition to active illumination to provide fail-safe operation should the IPM system lose power. Power Source IPM systems can derive power to operate through hardwired electrical connections, inductive wireless connections, or solar technology. To date, hardwired electrical connections and in- ductive wireless connections have outperformed (i.e., higher luminous intensity, more consistent operation) IPM systems relying on solar technology. Benefits to solar-powered IPM systems include the ease and flexibility of installation, par- ticularly for remote areas. Continued advancements in solar technology may make this a more viable IPM system power source in the future. System Controller and Enclosures The IPM system controllers are typically housed in a protec- tive cabinet or enclosure. For lightning protection, a ground box with copper ground rod is typically located near the cabinet/enclosure. In electrical storm-prone areas, lightning protection for IPM systems is especially important. Installation and Construction Methods Each IPM system vendor provides more detailed installation instructions tailored to its 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 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 40 the saw cut to adequately recess and protect the electrical cable and/or conduit. Individual unit solar-powered IPM sys- tems do not require this installation 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 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). 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 re- gions, where snowplowing is frequent, use of recessed mark- ers is necessary. Also, the performance of marker adhesives, particularly in unusually cold or hot temperatures, can have a significant effect on pop-off frequency. In most instances, manufacturers have been able to significantly 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 concrete barriers, sign posts, etc. IPM systems that use barrier- or post-mounted markers experienced signifi- cantly 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 con- crete cement pavement. Although the IPM systems observed in this synthesis effort included a range of pavement materi- als, no additional information was uncovered that described the comparative performance of IPM systems that were in- stalled in either portland concrete cement 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. Operation Modes System Activation Activation of IPM systems relies on either manual methods, where the system is activated 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 sen- sors, motion sensors, visual image video detection systems, in-pavement loop detectors, integration with traffic control

41 devices, and road-weather information systems. Manual acti- vation methods are typically lowest in cost, but require action from the road user to be effective. Passive activation meth- ods 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 in this synthesis effort included timer-based activation (in the case of a school zone) and ambient light-sensitive activation through the use of photoelectric cells to detect dusk (for acti- vation) and dawn (for deactivation). The nature of IPM system activation depends somewhat on the intended function of the system and the characteris- tics of the environment in which it is placed. Systems that are intended to guide road users are often operated contin- uously, particularly those in high-traffic environments. Con- versely, IPM systems that are intended to warn, regulate, or provide illumination are more commonly operated in- termittently, in response to a detected hazard or regulatory action, or to minimize environmental effects and energy consumption. Modes of Operation 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 (e.g., markers show red illumination when vehicles are required to stop). Varying flash rates (including steady burn) can indicate the level of hazard. Also, “chase” sequences can direct the road user to reduce 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 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 (i.e., to in- dicate wrong way travel). Use of multiple colors in the IPM system marker reduces the luminous intensity for any single illumination (i.e., a marker that contains 10 total LEDs would illuminate 5 LEDs of one color followed by 5 LEDs of an- other color). 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 up- stream speed sensors detect a vehicle traveling too fast for a curve or when a road-weather information system detects fog conditions) and may, depending on the manufacturer, pro- vide an adjustable increasing flash rate consistent with in- creasing danger (as long as the flash rate remains within an acceptable range). 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 il- luminated 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 applica- tions include horizontal curves, tunnels, merge areas, or con- struction work zones. In the IPM systems observed, use of white, amber, and red markers were noted, most commonly as single-color config- urations, although some of the markers provided dual-color illumination to coincide with the red and amber traffic signal indications. 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). Maintenance Requirements 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 environ- mental factors (e.g., water, dirt, and debris build-up) or traffic impacts. For markers located in the tire path of vehicles and particularly heavy vehicles, light source failure was partic- ularly 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 manu- facturer’s warranty. Annual maintenance costs for one IPM system were estimated to be $15,000, comprised largely of LED failure replacement costs. One jurisdiction reported significant delays in delivery of replacement parts. System markers that protrude above the ground have also experienced damage by street cleaners and snowplows. System manufacturers have moved to aluminum or stainless steel housing materials typically recessed into the pavement to ad- dress 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 systems do not require this same level of maintenance.

It was also noted that activities such as street repair or resur- facing require the IPM system to be removed and reinstalled or lost. This is not unique to IPM system applications, but challenges the longevity of any type of roadway instrumen- tation. Again, barrier- or post-mounted IPM systems are less likely to be affected by roadway repair or resurfacing activities. Costs Costs for IPM system applications range significantly, from $5,000 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 (e.g., solar) of power at the site; the condition of the pavement and any remedial actions required before IPM system installation; and traffic control requirements. In general, implementing agencies do not con- sider IPM systems to be a “low-cost” alternative to traditional traffic control devices and suggest that their use be limited to critical locations. Opportunities for federal funding to support IPM system implementation may be constrained by propri- etary issues (i.e., FHWA typically requires system bids from three or more vendors; patented products may not be approved for widespread implementation). Perceived and Measured Effectiveness Few formal evaluations have been performed to determine the effectiveness of IPM systems in enhancing roadway safety, operations, or aesthetics. Pedestrian crosswalk applications have been most frequently studied; IPM systems have gen- erally been shown to increase vehicle driver awareness, increase vehicle yielding, reduce vehicle approach speeds, reduce vehicle/pedestrian conflicts, and reduce pedestrian wait times. Considering broader applications of IPM systems, addi- tional studies have generally shown a reduction in vehicle speeds, improved lane-tracking, increased road user aware- ness, 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 purporting the effec- tiveness of IPM systems in enhancing various aspects of road- way 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 mainte- nance challenges encountered. Further, implementing agencies noted a high level of public support for and acceptance of IPM systems. 42 SUGGESTIONS Based on the information gathered through this synthesis effort, illuminated, active, IPM systems show potential for enhancing: (1) warning 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 prohibited; and (4) 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 a lack of installation, operation, and maintenance guidance is likely confounding system performance. As such, suggestions to focus future research and accelerate successful applications of IPM systems fall into two categories: (1) research and eval- uation and (2) standards and guidelines. Research and Evaluation • Development of a robust and standardized methodol- ogy for evaluating IPM systems would help to ensure that some level of consistency is achieved in the evalu- ation of these treatments. The functional breadth of more recent IPM system applications (i.e., to warn, guide, regulate, or provide illumination) requires an adaptable methodology that encompasses a wide range of perfor- mance measures. • Agencies that currently operate IPM systems are encouraged to evaluate their effectiveness and docu- ment subsequent findings so that others can benefit from their experiences. In lieu of a standardized eval- uation methodology, agencies could focus on obtain- ing a sufficiently large data sample over a reasonable observation period to enhance the credibility of their findings. • Additional research, with the following focus, could support subsequent development of IPM system guide- lines and standards: – Equipment specifications addressing the illumina- tion source, housing and lens, power source, system controller and enclosure; – Operational specifications addressing system acti- vation, marker color, marker flash rates, and chase sequences; – Installation methods including system layout and spacing; – Maintenance requirements; – Human factors (e.g., effects of glare and comprehen- sion); and – Safety (e.g., overdriving and collision with nonillu- minated objects). • Development of an Internet-based clearinghouse could support exchange of practical information (e.g., instal- lation lessons learned, annual maintenance costs, and

43 warranty recommendations) regarding IPM system use among public agencies. Standards and Guidelines • An expanded breadth and depth of coverage of IPM systems within the MUTCD is encouraged. The breadth of IPM system application and subsequent function suggests a similar required breadth in related standards and guidelines. • Warrants are likely not required or appropriate for IPM systems; IPM systems typically supplement existing traf- fic control treatments and/or devices. • Methods to describe the relationship between IPM sys- tems and other ITS devices and systems and promote their use within ITS architectures and planning efforts could be beneficial in encouraging implementation. These meth- ods could consider how IPM systems would interface with communications protocols and other equipment, and how they could provide feedback to transportation system operators to report operational status.

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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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