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Recommended Procedures for Testing and Evaluating Detectable Warning Systems (2010)

Chapter: Chapter 3 - Findings and Applications

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Suggested Citation:"Chapter 3 - Findings and Applications." National Academies of Sciences, Engineering, and Medicine. 2010. Recommended Procedures for Testing and Evaluating Detectable Warning Systems. Washington, DC: The National Academies Press. doi: 10.17226/22937.
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Suggested Citation:"Chapter 3 - Findings and Applications." National Academies of Sciences, Engineering, and Medicine. 2010. Recommended Procedures for Testing and Evaluating Detectable Warning Systems. Washington, DC: The National Academies Press. doi: 10.17226/22937.
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Suggested Citation:"Chapter 3 - Findings and Applications." National Academies of Sciences, Engineering, and Medicine. 2010. Recommended Procedures for Testing and Evaluating Detectable Warning Systems. Washington, DC: The National Academies Press. doi: 10.17226/22937.
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Suggested Citation:"Chapter 3 - Findings and Applications." National Academies of Sciences, Engineering, and Medicine. 2010. Recommended Procedures for Testing and Evaluating Detectable Warning Systems. Washington, DC: The National Academies Press. doi: 10.17226/22937.
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Suggested Citation:"Chapter 3 - Findings and Applications." National Academies of Sciences, Engineering, and Medicine. 2010. Recommended Procedures for Testing and Evaluating Detectable Warning Systems. Washington, DC: The National Academies Press. doi: 10.17226/22937.
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Suggested Citation:"Chapter 3 - Findings and Applications." National Academies of Sciences, Engineering, and Medicine. 2010. Recommended Procedures for Testing and Evaluating Detectable Warning Systems. Washington, DC: The National Academies Press. doi: 10.17226/22937.
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Suggested Citation:"Chapter 3 - Findings and Applications." National Academies of Sciences, Engineering, and Medicine. 2010. Recommended Procedures for Testing and Evaluating Detectable Warning Systems. Washington, DC: The National Academies Press. doi: 10.17226/22937.
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Suggested Citation:"Chapter 3 - Findings and Applications." National Academies of Sciences, Engineering, and Medicine. 2010. Recommended Procedures for Testing and Evaluating Detectable Warning Systems. Washington, DC: The National Academies Press. doi: 10.17226/22937.
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Suggested Citation:"Chapter 3 - Findings and Applications." National Academies of Sciences, Engineering, and Medicine. 2010. Recommended Procedures for Testing and Evaluating Detectable Warning Systems. Washington, DC: The National Academies Press. doi: 10.17226/22937.
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Suggested Citation:"Chapter 3 - Findings and Applications." National Academies of Sciences, Engineering, and Medicine. 2010. Recommended Procedures for Testing and Evaluating Detectable Warning Systems. Washington, DC: The National Academies Press. doi: 10.17226/22937.
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Suggested Citation:"Chapter 3 - Findings and Applications." National Academies of Sciences, Engineering, and Medicine. 2010. Recommended Procedures for Testing and Evaluating Detectable Warning Systems. Washington, DC: The National Academies Press. doi: 10.17226/22937.
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Suggested Citation:"Chapter 3 - Findings and Applications." National Academies of Sciences, Engineering, and Medicine. 2010. Recommended Procedures for Testing and Evaluating Detectable Warning Systems. Washington, DC: The National Academies Press. doi: 10.17226/22937.
×
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Suggested Citation:"Chapter 3 - Findings and Applications." National Academies of Sciences, Engineering, and Medicine. 2010. Recommended Procedures for Testing and Evaluating Detectable Warning Systems. Washington, DC: The National Academies Press. doi: 10.17226/22937.
×
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Suggested Citation:"Chapter 3 - Findings and Applications." National Academies of Sciences, Engineering, and Medicine. 2010. Recommended Procedures for Testing and Evaluating Detectable Warning Systems. Washington, DC: The National Academies Press. doi: 10.17226/22937.
×
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Suggested Citation:"Chapter 3 - Findings and Applications." National Academies of Sciences, Engineering, and Medicine. 2010. Recommended Procedures for Testing and Evaluating Detectable Warning Systems. Washington, DC: The National Academies Press. doi: 10.17226/22937.
×
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Suggested Citation:"Chapter 3 - Findings and Applications." National Academies of Sciences, Engineering, and Medicine. 2010. Recommended Procedures for Testing and Evaluating Detectable Warning Systems. Washington, DC: The National Academies Press. doi: 10.17226/22937.
×
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Suggested Citation:"Chapter 3 - Findings and Applications." National Academies of Sciences, Engineering, and Medicine. 2010. Recommended Procedures for Testing and Evaluating Detectable Warning Systems. Washington, DC: The National Academies Press. doi: 10.17226/22937.
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9Findings of Literature Review A literature search was conducted to locate published infor- mation on durability studies of detectable warning systems, including tests performed and results obtained. The literature generally took one of the following forms: syntheses and summaries, reports of field trials, reports of property-specific laboratory or field tests, and laboratory testing protocols. Syntheses and Summaries Detectable Warnings: Synthesis of U.S. and International Practice (Bentzen et al., 2000) discusses, in part, local percep- tions of durability of detectable warning systems. The authors conducted interviews with persons responsible for detectable warning system installation. Detectable warning systems were generally installed in the late 1990s and had often three or fewer years of service life at the time the interviews took place. While some of the particular products discussed are no longer on the market, the material and installation types represent products that are currently available and continue to be used. The report outlines several types of degradation, probable causes of degradation (as reported by the interviewees), and the geographic location of the detectable warning system. Several locations, both in the southern and northern regions of the U.S., reported color fading. Peeling of adhesive-applied systems was listed as a problem at multiple locations. Cracking was reported to be a problem in several areas and was felt to be related to freezing and thawing, snow removal, or the use of vehicles or carts over the detectable warning systems. NCHRP Project 20-7 (Estakhri and Smith, 2005) provided a synthesis of information from publicly available sources and interviews with Alaska DOT and New York DOT that are not available in other published sources. The report discusses material selection and durability concerns, among other topics. The most prominent degradation mechanisms outlined in the report are chipping of domes, removal of surface-applied systems, loosening of anchors, cracking and color fading. The report relates the deterioration mechanisms to both geographic location of the installation and the type of material. Reports of Field Trials Most of the reports reviewed by the research team involved field trials and assessments of various proprietary detectable warning systems performed by DOTs. These reports include general comments on the observed durability of the installed systems, and sometimes opinions were provided regarding the mechanisms of deterioration that caused degradation. However, the specific mechanisms or events that lead to the noted deterioration were not normally quantitatively docu- mented. Most studies involved periodic inspection of the detectable warning systems, and the events that led to specific types of degradation were not witnessed. While care was often taken to place detectable warning systems of different types in equivalent locations, the specific conditions for each detectable warning system were not identical. For example, snow removal methods (a significant source of degradation) often varied based on location. A summary of the durability findings of these DOT reports, along with information presented in Bentzen et al. (2000) and Estakhri and Smith (2005), is presented in Table 2. Reports of Property-Specific Laboratory or Field Tests Many reports related deterioration to snow removal. Studies by New Hampshire (Boisvert, 2003) and Illinois (IDOT, 2005) specifically studied the effect of snow removal operations on detectable warning systems by purposefully running a snow- plow over detectable warning systems in particular locations. The effect of the plowing on these locations was documented. In addition to the information provided in the published reports, communication with personnel from Wisconsin DOT C H A P T E R 3 Findings and Applications

10 Study Location System Types Type of Degradation Listed Source of Degradation New Hampshire (Boisvert, 2003) Surface-applied single domes, stamped concrete, polymer concrete, rigid polymer composite panel, flexible polymer mat, brick paver, precast concrete paver Damaged or missing domes Snow removal (study specially tested snow removal durability) Wisconsin (Kemp, 2003) Rigid polymer composite panel (cast-in-place and surface- applied), precast concrete paver, stamped concrete, flexible polymer mat, surface-applied single domes Coating abrasion, damaged domes, debonding, inconsistent dome shape (stamped concrete) Snow removal Vermont (Kaplan, 2004; Kaplan, 2006) Surface-applied single domes, flexible polymer mat, polymer concrete, rigid polymer composite panel, metal panel, stone paver Debonding of mats and single domes, dome damage, dome removal, removal of non-slip texture, color fading, bleeding of rust from cast iron panel, coating abrasion Snow removal, sun exposure Montana (Abernathy 2003; Abernathy, 2004a; Abernathy, 2004b; Abernathy, 2005) Flexible polymer mat, rigid polymer composite panel, surface single applied domes Dome wear, debonding of mats and single domes, coating loss, tearing of mats, loss of anchor pins, color fading Snow removal, sun exposure, freeze/thaw Oregon (Kirk, 2004) Surface single applied domes, flexible polymer mat Dome damage, color fading Not specified Illinois (IDOT, 2006) Rigid polymer composite (cast-in- place and surface-applied), metal panel, stone paver, precast concrete pavers Chipping of domes, removal of domes Snow removal (study focused on snow removal durability) Massachusetts Bay Transportation Authority (Ketola and Chia, 1994) Flexible polymer mat, ceramic tiles, polymer concrete, rigid polymer composite (surface- applied) Color fading, cracking, debonding, chipping, dome damage, pitting Snow removal, foot traffic, freeze/thaw, dirt accumulation Austin, Texas (Bentzen et al., 2000) Brick pavers Paver damage Truck traffic Claremont, California (Bentzen et al., 2000) Flexible polymer mat -- (newly installed system) -- (no data available) Metropolitan Atlanta Rapid Transit Authority (Bentzen et al., 2000) Rigid polymer composite panel Chipping, cracking, loss of anchors Steel wheeled carts Roseville, California (Bentzen et al., 2000) Rigid polymer composite panel Color fading Not specified Metro North Railroad (Bentzen et al., 2000) Rigid polymer composite panel Cracking, color fading, platform deterioration Freeze/thaw, snow removal, equipment, ultraviolet exposure Bay Area Rapid Transit (Bentzen et al., 2000) Flexible polymer mat, rigid polymer composite panel Delamination of mats, color fading Weathering, platform vibration, cleaning equipment Baltimore County, Maryland (Bentzen et al., 2000) Brick paver Dome wear Not specified Table 2. Summary of findings from published field trials.

(WisDOT) indicated that the State of Wisconsin has devel- oped a snowplow test in which a detectable warning panel is placed in a plywood jig and passed over 50 times with a truck-mounted plow. Only products that pass this test (based on visual evaluation) are approved by WisDOT. Two published studies involved lab testing, in addition to field trials. The first study focused on detectable warning sys- tems for mass transit systems, rather than for sidewalk usage (Ketola and Chia, 1994). The tests conducted were water soaking, bond strength, abrasion resistance, simulated cleaning, coefficient of friction, and impact resistance. The results of the testing and rationale for selecting certain tests were not discussed in detail in the publication. The second study was carried out by the State of Wisconsin, in conjunction with Minnesota DOT, and consisted of ultraviolet/condensation weathering tests (Kemp, 2003). The degree of color fading was measured instrumentally after the testing. Laboratory Testing Protocol The working notes from California’s Evaluation of Detectable Warnings Advisory Committee (EDWAC) are another sig- nificant source of information relevant to this project. This committee was set up under the California Division of the State Architect and was tasked with overseeing the development of a set of tests aimed at assessing durability of detectable warning systems. The California State Assembly charged the Division of the State Architect with developing a test methodology to demonstrate that shape, colorfastness, confirmation, sound- on-cane acoustic quality, resilience, and attachment will not degrade by more than 10% of the approved design charac- teristics over five years. While EDWAC and members of the public have identified other parameters that affect durability, the focus of the work has been on those criteria specifically outlined in the legislation. Meeting minutes and draft test standards are publicly available and were consulted by the research team. The most recent draft, published in February 2006, includes the testing methods and describes conditioning regimes for outdoor and indoor use (EDWAC, 2006). The outdoor testing regime consists of ultraviolet, chemical, abra- sion, elevated temperature, and optional freeze/thaw and optional salt spray exposures. The indoor testing regime con- sists of ultraviolet, chemical and abrasion exposures. Findings of Survey of State and Municipal Departments of Transportation Twenty-two representatives of state and municipal DOTs responded to a questionnaire requesting input regarding durability of detectable warning systems. The responses from state and municipal DOT representatives are summarized here. The responses came from all over the United States, with twelve responses from locations with cold, snowy winters, six responses from areas with hot summers and little to no snow in the winters, three responses from mainly temperate regions, and a response from the State of Utah, which experiences both significant snow in the winter in some regions and very hot summers in others. While the responses were grouped as above, it is recognized that the climatic conditions often vary throughout a state, and many states may contain both hot and cold weather regions. The respondents were questioned on their perception of the most critical deterioration mechanisms. As summarized in Table 3, snow removal, ultraviolet/sun exposure, freezing and thawing, and abrasion from foot traffic were identified as the four most critical deterioration mechanisms. Unsurprisingly, the fourteen respondents who consider snow removal a key deterioration mechanism are from states where cold weather is common, such as Ohio, Illinois, and New York, while the respondents who did not consider snow removal an issue come from climates where snow is less common, such as Arizona, 11 Study Location System Types Type of Degradation Listed Source of Degradation Cleveland, Ohio (Bentzen et al., 2000) Brick paver Loose pavers Truck traffic Harrisburg, Pennsylvania (Bentzen et al., 2000) Stamped concrete (fabricated off- site into pavers) Wear, settling, cracking, broken domes Truck traffic, other Alaska (Estakhri and Smith, 2005) Precast concrete paver, rigid polymer composite panel, surface-applied single domes, flexible polymer mat Dome damage, delamination of mats, adhesive deterioration Snow removal, weathering, extreme cold temperatures New York (Estakhri and Smith, 2005) Rigid polymer composite (cast-in- place), precast concrete paver, polymer concrete, brick paver, flexible polymer mat Delamination of mat, dome wear, dome removal Snow removal and other Table 2. (Continued).

Nevada, and Washington. The respondents who list ultraviolet/ sun exposure as a key deterioration mechanism are from all over the country, including areas, such as New Jersey, that experience cold winters. The respondents concerned with abrasion from foot traffic are from locations throughout the United States. Some respondents specified “other mechanisms,” which varied from problems with water staining and poor adhesion to the walking surface, to cracking from heavy vehi- cles traveling over the detectable warning system. The responses to the key deterioration mechanisms vary by geographic location. This highlights the need to have a testing approach that considers more than one exposure category, so an appropriate testing methodology can be chosen for locations where certain deterioration mechanisms may be prevalent. Environmental conditions vary throughout the country, with snow and cold weather common in the northern parts of the country, while high temperatures and high ultraviolet expo- sure is common in the southern part of the country. While environmental conditions vary, all areas of the country suffer from some common deterioration mechanisms, such as abra- sion from foot traffic, and this needs to be considered for all geographic locations. In addition to requesting information on deterioration mechanisms, the questionnaire also requested responses as to opinions of the most critical material properties that influ- ence durability of detectable warning systems. A summary of the responses is presented in Table 4. Three-quarters of the respondents selected slip resistance as a critical material property. It is obviously important for a walking surface to maintain slip resistance and not endanger pedestrians. Freeze/thaw resistance was the next most frequently cited material property. While cited as a material property, freeze/thaw resistance is a function of both the material itself and the detectable warning system/sidewalk system. Nine of the thirteen respondents who selected freeze/thaw resistance as an important material property are from “cold” regions. The questionnaire also requested information on how the respondents select detectable warning systems. A summary of responses is presented in Table 5. Many respondents (12 out of 22) indicated that they choose detectable warning systems based on discussions with suppliers. Fifteen respon- dents indicated that they reviewed manufacturer’s product literature to aid the decision-making process. Most respondents (18 out of 22) use field trials to evaluate various detectable warn- ing systems. Many respondents use more than one method to select detectable warning systems for use in their location. Only four states were found to rely on lab or field tests in addition to field trials: New York, which tests contrast ratio; Georgia, which tests physical dimensions; Wisconsin, which tests snowplow resistance; and Minnesota, which tests ultraviolet/condensation, chemical resistance, wear resistance, freeze/thaw exposure, water absorption, impact resistance, and snowplow exposure. Four locations (Nevada, Florida, New York, and Cincinnati, Ohio) reported that they require test data to be submitted by the material supplier prior to approval of a product. The data required varies based on department and on the types of materials systems approved. Nevada has specifications for the compressive strength of precast pavers and coefficient of friction and several proposed specifications for polymeric materials, which are not on the approved list but are under consideration, which would include tests for artificial weather- ing, chemical resistance, water absorption, tensile strength, compressive strength, color, impact resistance, and salt fog resistance. Florida DOT requires manufacturers to provide data on coefficient of friction, wear resistance, water absorp- tion, bond strength and artificial weathering. New York DOT requires manufacturers to submit certified test data and has different requirements for cast-in-place units and surface- applied units. For cast-in-place units, data on compressive strength and freeze/thaw testing must be supplied. For surface- applied units, test data on wear resistance, coefficient of friction and bond strength must be supplied. The City of Cincinnati 12 Deterioration Mechanism Number of Responses* Snow removal 14 Freeze/thaw 10 UV/Sun exposure 9 Other 9 Abrasion from foot traffic 7 Extreme temperatures 6 Thermal cycling 5 Abrasion from vehicle traffic 3 * out of 22 total responses Table 3. Deterioration mechanisms reported as important. Material Property Number of Responses* Slip resistance 16 Freeze/thaw resistance 13 Compressive strength 11 Flexural strength 11 Fade resistance 10 Chemical resistance (deicers, cleaning chemicals) 7 * out of 22 total responses Table 4. Material properties reported as critical. Method of Selecting Detectable Warning Systems Number of Responses* Field trials 18 Product literature 15 Discussions with suppliers 12 Lab tests 3 * out of 22 total responses Table 5. Methods of selection used by agencies.

has requirements for brick pavers including water absorption, freeze/thaw resistance and general conformance to ASTM C 902 Standard Specification for Pedestrian and Light Traffic Paving Brick Class SX, Type I. Discussion of Findings of Literature Review and Survey The findings of the literature review and survey were sum- marized in terms of the deterioration mechanism judged sig- nificant to the durability of detectable warning systems and in terms of the range of detectable warning system products that the test protocol may be used to evaluate. Deterioration Mechanisms Several deterioration mechanisms were reported in the literature review and in the survey: • Freezing and thawing • Snow removal • Exposure to ultraviolet radiation • Abrasion • Impact • Exposure to extreme temperatures • Thermal cycling • Exposure to moisture • Exposure to chemicals (including deicers) • Vehicle traffic • Settling and displacement of pavers Displacement of pavers can be primarily an installation or a water drainage issue and will not be considered for the pur- poses of this study. The others are a result of environmental exposure and have been considered during development of the exposure regimes and evaluation tests. Detectable Warning System Products The literature review and survey identified many materials and system types. Table 6 lists the products currently approved or preferred by the survey respondents. In addition to these products, the research team conducted a review of the products currently marketed as detectable warn- ing systems. An Internet survey of the products currently on the market provided useful information on the types of systems 13 Location Approved or Preferred Products Vineland, New Jersey Metal panels Princeton, New Jersey Metal panels, rigid polymer composite panels (surface-applied) Arkansas Rigid polymer composite panels (cast-in-place) Texas Rigid polymer composite panels (cast-in-place and surface-applied), flexible polymer mat, brick pavers, precast concrete pavers, metal panels Montana Metal panels Illinois No specific products South Dakota Precast concrete pavers Colorado Precast concrete pavers, brick pavers Arizona Rigid polymer composite panels, ceramic panels, steel panels, stone pavers, polymer concrete panels, single anchored domes, precast concrete pavers Nevada Precast concrete pavers, brick pavers Florida Rigid polymer composite panels, flexible polymer mats, precast concrete pavers, brick pavers, metal panels Oregon Rigid polymer composite panels, single surface-applied domes, flexible polymer mat, ceramic panel, polymer concrete, precast concrete pavers Wyoming Metal panels, ceramic panels, precast concrete pavers, rigid polymer composite panels Cincinnati, Ohio Brick pavers, rigid polymer composite panels, metal panels, surface-applied single domes Bellevue, Washington Rigid polymer composite panels, flexible polymer mats Georgia Metal panels, rigid polymer composite panels (surface-applied and cast-in-place), flexible polymer mat Utah Precast concrete pavers West Virginia No response Delaware Metal panels, pavers Rhode Island No response New York Rigid polymer composite panels (surface-applied and cast-in-place), flexible polymer mat, single surface-applied domes, stamped concrete, brick pavers, precast concrete pavers, polymer concrete, metal panels Minnesota Metal panels, polymer concrete Table 6. Approved or preferred products listed by survey respondents.

(methods of attachment) as well as the types of materials used in detectable warning systems. Methods of Attachment Detectable warning systems can be broken down into the following system types by the method of attachment to the sidewalk: • Prefabricated panels that are cast into plastic concrete (cast-in-place) • Surface-applied systems, consisting of: – Rigid panels that are attached to cured concrete by an adhesive system and sometimes supplemental anchors – Flexible panels that are attached to cured concrete by an adhesive system and sometimes supplemental anchors – Single domes that are attached to cured concrete, with a coating applied over the domes and concrete. Domes are attached with adhesive, cast directly onto the concrete, or attached with mechanical anchors. • Pavers that are supported on a sand setting bed, bituminous setting bed, or thin set mortar • Domes formed by imprinting plastic concrete (stamped concrete) Systems that are cast-in-place or stamped can only be applied to new sidewalk construction; if a retrofit of an exist- ing sidewalk is desired, the old concrete must be removed and replaced with new concrete. Systems that are surface applied can be applied to existing concrete with a varying amount of surface preparation required, according to the manufac- turer’s installation instructions. The use of precast pavers may require replacing the sidewalk concrete, or may be retrofit, depending on the geometry of the previous installation (for example, non-truncated dome pavers may be replaced with truncated dome pavers). Material Types Reported A significant variation in the types of materials from which detectable warning systems are fabricated exists. The main material types can be grouped into the following categories: • Stamped concrete (standard sidewalk concrete with a formed truncated dome surface). The concrete may be integrally colored, or a colored coating may be applied to the surface. • Flexible polymer mats. These mats are applied to the concrete surface with adhesive and may be integrally colored, or a colored coating may be applied to the surface. • Surface-applied domes with a polymeric-based coating on the surface. A number of materials are used for the domes, including rubber, polymer, ceramic and aluminum. • Metallic systems. These systems are cast-in-place or surface applied, consist of stainless steel or cast iron and may be coated or left bare to form a natural patina in the case of cast iron. • Rigid polymer composite panels. These materials consist of rigid polymer matrices with fiberglass or other reinforce- ment. These systems may be cast-in-place or surface applied and are integrally colored. • Polymer concrete. These systems consist of sand in a poly- mer matrix, may be surface applied or cast-in-place and are integrally colored. • Pavers. This general type encompasses precast concrete pavers, brick pavers and stone (granite) pavers. These systems may be attached with a setting bed, bituminous setting bed, or thin set mortar. Pavers are generally integrally colored. • Ceramic panels. These systems consist of ceramic panels that are adhered to fresh concrete with setting pins. Only one product remains on the market. Summary of Proposed Test Methods To support the development of the test protocol, the pro- posed test methods were conducted on samples representing a range of detectable warning systems. The testing procedures were refined based on the experience gained during this effort. The refined test methods were then presented as recommended methods of test and are provided in the attachment to this report. The following discussion outlines the specific need for each test method and its key objectives, and provides a brief summary of the method. Further discussion regarding the development of each test method is given in the appendix. Durability of Detectable Warning Systems (Master Test Method) For detectable warning systems to function properly and to serve as a safe walking surface, the following properties are essential: color contrast, slip resistance, mechanical integrity and dimensional stability. Environmental exposures and traffic-related forces may trigger deterioration mechanisms that have a deleterious effect on these properties. These deteriora- tion mechanisms are expected to interact, making long-term in-service behavior difficult to predict. The key objectives in the development of the test protocol for evaluating durability of detectable warning systems were (1) to consider significant deterioration mechanisms, (2) to replicate the potential inter- action of deterioration mechanisms, (3) to provide a universally applicable method that could be used to compare currently known product designs regardless of material or anchorage, and (4) to permit flexibility in the interpretation of the test results relative to local requirements and environmental conditions, as well as future findings. 14

The protocol tests detectable warning systems installed in or applied to concrete slabs. Two types of test methods are used. The first type of method is the evaluation test, which measures a specific property or quality. The evaluation tests are further characterized as non-destructive evaluation tests—which include visual and microscopic evaluation, color measurement, dome shape and geometry measurement and slip resistance— and destructive evaluation tests—which include system bond (no method finalized), coating and single dome bond, resistance to impact from a falling tup, wear resistance and resistance to impact from a falling snowplow blade. The second type of method is the exposure regime, which simulates the effects of in-service exposure but does not include an evaluation phase. The evaluation tests are used to quantify the effects of the exposure regimes. The exposure regimes consist of freeze/thaw, high temperature thermal cycling, ultraviolet light exposure, and abrasion exposure. The execution of the test protocol requires preparation of two detectable warning system/concrete slab specimens for each product in a manner that replicates the manufacturer’s rec- ommended procedures. The non-destructive evaluation tests are then performed on these unexposed samples. (Optionally, the destructive evaluation tests can also be performed on un- exposed samples, but this requires additional slab specimens.) The samples are then subjected to four sequential cycles of the exposure regimes, with each cycle consisting of one quarter of the full exposure duration. At the conclusion of each quarterly exposure cycle, all evaluation tests are performed and sub- sequently used to assess durability and performance of the detectable warning systems. The specific details of exposure regimes are determined by the exposure category, which is selected by the user based on anticipated environmental conditions where the detectable warning system will be used. Two broad categories, named “hot” and “cold”, are identified and are intended to represent the environmental extremes observed in the United States. For the hot exposure category, the duration of the ultraviolet exposure is greater, the maximum temperature defining the high-temperature thermal cycling test is higher, and the freeze/thaw exposure and resistance to impact from simu- lated snowplow blade evaluation tests are not included. The test methods for each exposure category are given in Table 7. The full exposure durations for each category are outlined in Table 8. Part 1—Freeze/Thaw Durability Repeated freezing can cause cracking and degradation of the detectable warning system as water trapped in the system undergoes volumetric expansion. The freeze/thaw durability test method is intended to recreate conditions that might cause freeze/thaw damage and expose the samples to deicing chemicals. 15 Test Method Hot Exposure Category Cold Exposure Category Non-destructive Evaluation Test Visual and Microscopic Evaluation Yes Yes Dome Shape and Geometry Measurement Yes Yes Color Measurement Yes Yes Slip Resistance Yes Yes Destructive Evaluation Test Coating and Single Dome Bond Yes Yes Resistance to Impact from Falling Tup Yes* Yes Wear Resistance Yes Yes Resistance to Impact from Simulated Snowplow Blade No Yes System Bond Yes** Yes** Exposure Regimes Freeze/Thaw No Yes High Temperature Thermal Cycling Yes Yes Ultraviolet Light Exposure Yes Yes Abrasion Exposure Yes Yes * Tests performed at room temperature only ** No method finalized Table 7. Exposure category for each test method. Exposure Regime Hot Exposure Category Cold Exposure Category Freeze/Thaw (None) 60 cycles High Temperature Thermal Cycling 60 cycles 25-93ºC (77–200°F) 60 cycles 25-77ºC (77–170°F) Ultraviolet Light Exposure 1500 hrs 1000 hrs Abrasion Exposure 16 passes 16 passes Table 8. Total exposure duration for each exposure category.

The proposed method consists of a freeze/thaw test where the concrete/detectable warning system samples are ponded or submerged in sodium chloride solution and subjected to repeated freezing and thawing cycles. The entire top surface of the specimen is ponded or submersed for the full duration of the test, to allow water to penetrate around any attachments, gaps, joints, or cracks in the detectable warning system/concrete composite system. Water that freezes underneath the detectable warning system may lead to “freeze-jacking,” whereby upheaval, cracking or distortion of the detectable warning system occurs as the water volume expands during the freezing process. During the test, the system is held below freezing until the solution ponded on top of the detectable warning system has frozen completely. The samples are then held at a thawing temperature until the solution has completely thawed. A repre- sentative plot of this freeze/thaw cycle is shown in Figure 4. This freeze/thaw cycle is repeated for a total of sixty times, fifteen times for each exposure cycle of in the test protocol. The freeze/thaw resistance test is not intended to be conducted to evaluate performance in the hot exposure category. Part 2—High Temperature Thermal Cycling Thermal cycling may cause restraint-related deterioration as a result of differential thermal expansion of the detectable warning system and the concrete sidewalk. High temperatures induced by radiant exposure may also cause degradation and softening of materials or adhesives. The high temperature thermal cycling test is designed to simulate the effects of cyclical variation in temperatures on detectable warning systems fixed to a concrete substrate using a control cycle defined independ- ently of system characteristics. Detectable warning systems are subjected to thermal cycling between specified temperatures, with the maximum tem- perature varied based on the exposure conditioning category. Specimens are irradiated with heat lamps to provide surface heating. The exposure is controlled based on insulated black panel thermometers, allowing the irradiation to be controlled independently of the detectable warning system properties. After the heating cycle, the specimens are cooled with flowing water, which produces both a thermal shock as well as exposing the materials to moisture. Photographs of the test apparatus during heating and cooling cycles are shown in Figures 5 and 6, respectively. The basic test cycle, which is repeated a number of times based on the exposure conditioning category, consists of the following steps: Ramp—Heat the specimen until an insulated black panel thermometer placed on the surface of the specimen reaches the desired maximum temperature, which is 93°C (200°F) for the hot exposure category and 77°C (170°F) 16 -20 0 20 40 60 80 100 0 5 10 15 20 25 30 35 40 Te m pe ra tu re (F ) Hours Slab Solution Chamber Figure 4. A plot of the freeze/thaw durability test temperatures.

for the cold exposure category. This heating must be performed within a set time period. Soak—Maintain the temperature of the insulated black panel thermometer for a set time period. Cool—Cool the specimen until the central thermocouple embedded in the concrete reaches a baseline tempera- ture of 25°C (77°F). After this temperature is reached, the cycle repeats. Part 3—Ultraviolet Light Exposure Ultraviolet (UV) exposure can cause color fading, surface cracking, or other general material degradation. The objective of the UV light exposure is to simulate exposure to the UV radiation in sunlight. The UV light exposure is conducted according to ASTM G 151-06 Standard Practice for Exposing Nonmetallic Materials in Accelerated Test Devices that Use Laboratory Light Sources and ASTM G 154-06 Standard Practice for Operating Fluorescent Light Apparatus for UV Exposure of Nonmetallic Materials. UV lamps are positioned at a fixed distance above the detectable warning system surface. The lamps are UVA-340 fluores- cent lamps that are intended to simulate sun exposure in the UV-A region. These lamps are the same and the distance is similar to a conventional commercially available UV weather- ing cabinet. The systems are placed in an enclosure to protect worker’s eyes from the UV radiation and maintain constant exposure conditions for the specimens. The enclosure used for test development is shown in Figure 7. The duration of irradiation is different for the hot and cold exposure categories. The hot exposure category has a 50% longer duration of UV irradiation than the cold exposure category. Part 4—Abrasion Exposure Abrasion from foot traffic or wheeled traffic can reduce overall dome height and alter the surface texture of detectable warning systems. The method discussed in this section is the abrasion exposure and is contrasted with the wear resistance test, which is an evaluation test. The objective of the abrasion exposure is to simulate wear of the dome surface in a progres- sive and realistic way, so that other wear-triggered exposure- related deterioration mechanisms could manifest. The proposed test method consists of a laboratory-based exposure test where a fixed weight sled, consisting of aluminum oxide abrasive paper mounted against a sheet of compressible 17 Figure 5. High temperature thermal cycling enclosure and sample under heating (ramp) portion of test cycle. Figure 6. High temperature thermal cycling enclosure and sample under cooling portion of test cycle (note the sheet of water draining to the left on the sample surface). Figure 7. Interior of the UV light exposure enclosure.

18 foam attached to a rigid plate, is translated across the surface of the system by a hand-operated dolly and cable system. The foam allows the sandpaper to partially conform to the tops of the domes. The test apparatus is shown in Figure 8. This sled, which is sized to cover half of the nominal 24-inch wide typical detectable warning system, is cycled back and forth over the surface of first one half of a system and then the other half. For informational purposes only, the effect of the abrasive action can be assessed by measuring the height of domes before and after exposure. Part 5—Visual and Microscopic Evaluation Visual and microscopic evaluation is needed to observe conditions that develop as a result of the exposure cycles that are not readily measured by other techniques, such as cracking or changes in elevation of the detectable warning system in the concrete. Visual examination is carried out on as-fabricated specimens and consists of examining the specimens for discoloration, cracking, surface distress and other evidence of degradation. Any unusual features prior to exposure, including local dis- coloration, chips, cracks, and other features are marked on a data sheet. Test specimens are photographed to document conditions. Microscopic evaluation is performed with a portable 10X to 30X magnification field microscope on two spots, approximately one square inch each, on the specimen sur- face. Microcracking or other forms of surface distress are observed with the field microscope. Similar microscopical examinations are conducted and documented after exposure and are compared to observations made prior to the exposure regime. Part 6—Color Measurement Excessive color fading can reduce the color contrast of a dark-on-light system and may lead to non-compliance with adopted specifications. The objective of the color measurement is to provide useful color data for comparison of the detectable warning system surfaces. The method consists of measuring the color of domes and field areas of a detectable warning system using a colorimeter. The CIELAB system is used to measure color. Measurements are made on ten dome or field areas, and the L*, a*, and b* values are averaged because the surfaces of many detectable warning system products are very rough and, even with an instrument with an integral light source, readings may vary somewhat because of the roughness. Averaging the results of ten readings minimizes the effect of the variability in the readings. Color difference as a result of exposure is measured as the change in lightness, ΔL*, the change in redness/greenness, Δa*, the change in yellowness/blueness, Δb*, or the overall change in color, ΔE. The overall change in color, ΔE, is sug- gested as the means for estimating color change, although individual agencies may find differences in one of the other coordinates more useful. For example, if only yellow detectable warning systems are allowed under specification, an agency may find Δb* more useful, or for agencies that specify any color or range of colors, ΔL* may provide a measure of fade from dark to light. Part 7—Dome Shape and Geometry Measurement Measurement of the shape and dimensions of the trun- cated domes is required to evaluate compliance with specifi- cation requirements. Additionally, shape measurements can be used to quantify damage to domes as a result of exposure or evaluation tests. The shape test method is referenced by a number of the other test methods. The dome diameter at the base, dome diameter at the top, and inter-dome spacing are measured with calipers. The rounded shape of some domes makes it difficult to identify the dome top and dome base for diameter measurements with precision, because edges may not be clearly delineated. Operator judgment will be relied upon to take measurements at the top and the base. Four domes will be measured and the values averaged. The averaging of multiple readings will Figure 8. Abrasion exposure setup.

accommodate slight differences in dome dimensions and operator uncertainty in measurement. Measuring the dome diameter at the base with calipers is shown in Figure 9. The dome height is measured with a depth gauge mounted to a steel plate that can be placed over the top of four domes. The gauge spindle point rests on the bottom of the field, while the plate rests on the highest feature on the top of the domes. Figure 10 shows the depth gauge on a detectable warning system. Part 8—Coating and Single Dome Bond Detectable warning systems may be coated or consist of an array of individually adhered surface-applied single domes. Coatings may become degraded and surface-applied single domes may lose adhesion caused by several degradation mechanisms. The coating and single dome bond test was developed to measure bond strength of coatings and surface- applied single domes. The proposed method consists of adhering dollies to the surface of the detectable warning system that are then pulled off in direct tension. A Type V tension tester, described in ASTM D 4541 Standard Test Method for Pull-Off Strength of Coatings Using Portable Adhesion Testers, provides a reading of the pull-off force required to overcome the bond of the coating to the system. This force is converted to a pull-off strength based on the area of the dollies or the equivalent diameter of the surface area stressed. Testing is carried out in triplicate on the tops of the domes and also in triplicate on the field between domes, because the adhesion may be different in these areas. Schematics for testing the coating bond on the tops of the domes and on the field and for testing the bond of surface- applied single domes are provided in Figure 11. Tests are carried out at room temperature (approximately 21–27°C [70–80°F]) and also at elevated temperature (60°C [140°F]). 19 Figure 9. Dome shape and geometry measurement (measuring the dome base diameter). Figure 10. Dome shape and geometry measurement (measuring the dome height). Figure 11. Schematic of coating bond tests.

This test method has been adapted to test the adhesion of surface-applied single domes to the concrete surface. If coating is present on the top of the domes, the domes are tested with the coating in place and with the coating removed with abrasive paper to isolate the dome/substrate interface. Direct tension is applied to the dolly bonded to a single dome until failure. Part 9—Slip Resistance Slip resistance is an important factor in preventing a pedes- trian from falling on a walking surface. The slip resistance test was developed to measure the coefficient of friction on both the field and tops of domes with a test apparatus adjustable to the range of allowed geometries. Slip resistance is measured in general accordance with ASTM F 609-05 Standard Test Method for Using a Horizontal Pull Slipmeter (HPS). A modified slipmeter is used to measure coefficient of friction on both the tops of the domes and the field. The Neolite rubber feet are adjustable such that all three feet can be placed on dome tops or the field of detectable warning systems of all allowable dome sizes and spacings. Figure 12 shows the slipmeter on a representative detectable warning system. Each coefficient of friction measurement is obtained by av- eraging readings performed in four perpendicular directions. Two sets of measurements are taken on both the domes and the field. These eight measurements are reported separately and are averaged to obtain an overall coefficient of friction for the domes and a separate overall coefficient of friction for the field. Part 10—Resistance to Impact from Simulated Snowplow Blade Snow removal operations are considered to be a signifi- cant source of degradation of detectable warning systems in northern states. Snow removal has been reported to chip and remove domes, to remove colored coatings, and to peel and, in some cases, remove surface-applied products. The test for resistance to impact from simulated snowplow blade was developed to produce an accurate representation of the dynamic nature and lateral directionality of the snowplow impact process. The proposed test method consists of a laboratory-based snow removal resistance test where an impactor (called the “strike plate”), simulating a snowplow blade and mounted on a pendulum, impacts single domes of detectable warning system/concrete composite systems. The pendulum is designed to simulate the movement of a snowplow blade, so that the strike plate impacts the dome moving in the plane parallel to the surface of the detectable warning system. The pendulum shaft is constructed so as to allow upward vertical movement of the impactor, such that the impactor can “bounce” upward and lift over the surface of the tested dome at impact. This type of dynamic movement is consistent with that of actual plows, which continue to move over the system after making initial contact. The pendulum consists of two connected rigid arms: (1) a rotating arm and (2) a rotating-translating arm. The rotating arm is mounted to an axle and the rotating-translating arm is attached to the rotating arm by a connection that allows the rotating-translating arm to move along the axis of the pendulum arms. The test apparatus is shown in Figure 13. The test is conducted at below-freezing temperatures and a total of three domes on the edge of the samples are impacted during a single test series. The type and extent of damage is ranked from A (least damage) to F (greatest damage) for each of these domes by comparison with standard schematics. The effect of the impact is also documented photographically. The snow removal resistance test is not intended to be con- ducted to evaluate performance in the hot exposure category. Part 11—Resistance to Impact from Falling Tup Detectable warning systems are subject to impact from a variety of sources that may damage the system surface. The test for resistance to impact from falling tup was adapted from a standard test method for conducting impact testing on detectable warning system/concrete composites. The proposed test method consists of an impactor that is dropped onto domes of the detectable warning system/concrete 20 a) b) Adjustable feet Figure 12. Evaluating slip by the slipmeter (note that the adjustable Neolite feet are centered on the tops of the domes).

system. The energy of impact is controlled by a combination of impactor mass and drop height. The tup is a standardized, 25 mm (1-inch) diameter hardened steel hemisphere. Each set of tests consists of impacting three separate domes at each of three impact energies. The test apparatus and a close-up view of the impactor are shown in Figures 14 and 15, respectively. For the testing according to the cold exposure category, tests are carried out at both room and freezing temperatures. The freezing impact resistance test is not intended to be conducted to evaluate performance in the hot exposure category, although tests at room temperature are still performed. Part 12—Wear Resistance As noted in the previous section discussing the abrasion exposure, abrasion is a significant source of degradation of detectable warning systems. The evaluation test, which is dis- cussed in this section, quantifies the resistance of a detectable warning system to abrasion in a rapid, controlled, and con- sistent manner. The proposed destructive test method evaluates the surface of a 150 mm (6-inch) diameter specimen cored or otherwise cut from a detectable warning system/slab sample. This surface specimen is held with a fixed weight against an aluminum oxide abrasive sand paper affixed to a standard lapping wheel, which is rotated at a fixed speed for a specific number of revolutions. The specimen is rotated intermittently during the test to ensure even abrasion. The wear resistance of the detectable warning system is assessed by measuring the dome height before and after the test. A photo of the wear resistance test apparatus is shown in Figure 16. Part 13—System Bond Measurement System bond describes the adhesion or anchorage of the detectable warning system to the concrete substrate. There are a wide range of methods by which the currently available sys- tems are fixed in place. While a detectable warning system is unlikely to ever experience an upwardly directed vertical load in its service life, measurement of the relative system direct tension bond strength is important for evaluating relative durability of different detectable warning systems. Direct tension bond strength of a system is judged to have direct correlation with the overall structural integrity. 21 Release mechanism Strike plate Rotating- translating arm Strike plate Rotating arm Connection Axle Figure 13. Apparatus to test impact resistance to a simulated snowplow blade.

Difficulties in obtaining repeatable results, representative of the full system response, prevented finalization of a method. The data for the bond testing varied significantly between the five different systems included in the development, as well as within a single material when repeated tests were performed. This is partially attributable to the varying methods of anchor- ages employed by each system. Because of the wide disparity of bond forces results, efforts were made to normalize the strength per anchor or unit length of anchorage. These results were also divergent. More discussion of these difficulties is provided in the appendix. No final method has been proposed. Guidance on Interpretation of Test Results Little laboratory testing of detectable warning systems has been carried out in such a way to support objective comparisons or predictions of future performance. Most municipalities that do perform testing use in-situ trial installations that are monitored for one or more years to qualitatively assess dura- bility, but unfortunately without quantifying the exposure conditions. There are no published data available to scientif- ically correlate performance in laboratory tests to expected field performance and in-service longevity. As laboratory testing becomes more prevalent and methodologies more consistent, the results of these tests can be used to compare laboratory performance with reported performance in field installations. At this time, without the necessary correlation to field per- formance, the results of the laboratory tests cannot be used to 22 Figure 14. Apparatus to test impact resistance of a falling tup. (The metal guide tube is indicated with an arrow. The casters allow easy positioning of the impactor over the detectable warning system. The mass and tup have been retracted through the guide tube.) Figure 15. View of the falling tup for the resistance to impact test. Figure 16. Wear resistance sample frame assembly.

confidently predict a specific service life under particular site conditions. Variability in field installation, field service conditions and interaction of the effects of environmental exposure creates additional challenges in predicting service life of detectable warning systems. Inconsistencies in the installation process, such as poor consolidation of the concrete below a cast-in-place system or air bubbles under a surface-applied system, can be expected to affect durability in an unpredictable manner. Because there is likely to be an interaction between exposure- related deterioration mechanisms, an attempt was made to include reasonable severity levels in the exposure protocol. However, the interaction between these effects is not fully understood. This protocol includes both hot and cold categories to address variable climate conditions. However, the environ- mental climates across the United States vary widely making complete representation by only two exposure categories impossible. Other exposure conditions, such as the degree of foot traffic or amount of small vehicle traffic (such as carts), will vary depending on the location of the detectable warning system. The ability of the protocols proposed herein to simulate actual exposure conditions is uncertain, and future work is needed to provide a better understanding of the relationship between laboratory testing and field performance. Nevertheless, this protocol was developed to provide a basis for comparing performance in a uniform test program, and some guidance has been provided in the appendix to support the interpretation of the results of testing relative to in-service performance. Combining Test Results Products tested using this protocol can be compared to one another on a test-by-test basis, but it is clearly desirable to determine a ranking for comparing the overall performance of the systems. If only one test was performed, the performance of the systems could be compared based on the measured value of that test for each system. However, since multiple evaluation tests are included in this protocol, a method of combining the responses (test results) from the different tests is needed. The best choice for a given installation must be based on weighting the importance of the various durability- related properties and the anticipated performance, as well as consideration of aesthetics, initial cost, ease and quality of installation, maintenance requirements, replacement cost, and other factors. This testing protocol focused on an assessment of the durability of the systems; therefore, a method for devel- oping a combined rating of durability is proposed. Many options for performing such a combination are possible, but the procedure presented here is intended to allow the user great flexibility in interpretation of the protocol test results and in the assignment of the importance of the test response to overall performance so that local specifications, conditions, and preferences may be addressed. Ratings Many of the tests performed during this program were devel- oped to simulate the unique conditions that are important to the durability of detectable warning systems. No industry-accepted or proven guidance has been developed for the interpretation of test results and prediction of in-service performance. Accord- ingly, the research team has applied engineering judgment in evaluating the absolute and relative test data and developed a system for assigning a rating for each evaluation test result based on whether that response is expected to meet a criterion of “acceptable performance.” For the purposes of this project, “acceptable performance” refers to serviceable, functional and durable use within the environment represented by the selected exposure category for approximately five years or more. It is emphasized that the research team’s conclusions are an estimate based on results of the test methods that are newly developed and this protocol has not been compared to a systematic study of the performance of detectable warnings in service. The performance of each product may be rated in each of the evaluation tests included in this program. The system proposed to characterize the performance is based on ratings of 0 to 4. The assigned performance level of each of the ratings is: • 4 for a product that is likely to significantly exceed acceptable performance • 3 for a product that is likely to slightly exceed acceptable performance • 2 for a product that is likely to produce acceptable performance • 1 for a product that is likely to produce slightly less than acceptable performance • 0 for a product that is not likely to produce acceptable performance. Correlation tables providing guidance for applying ratings for each evaluation test result have been provided with the discussion given in the appendix. It is anticipated that the cor- relations between test results and ratings may need revision in the future as experience with the protocol and field per- formance grows. Agencies specifying these tests may consider developing correlation tables to adapt the interpretation of test responses to reflect their own specific needs. Two evaluation test methods that are not easily interpreted and assigned numerical ratings are the visual and microscopic evaluation and the dome shape and geometry measurement. The visual and microscopic evaluation is subjective and may identify too wide a range of possible features or defects for a correlation table to be developed. For this reason, anticipated 23

performance ratings are not assigned using the same incremen- tal scale. Rather, the evaluation is set up as a pass/fail result, with the test result being assigned either a 2 (likely to produce acceptable performance) or a 0 (not likely to produce acceptable performance). The dome shape and geometry measurement has also been set up as a pass/fail test. The dome shape is spec- ified by each agency, and geometries within the specified range are considered a 2 (likely to produce acceptable performance), while geometries outside the specified range are considered a 0 (not likely to produce acceptable performance). The dome shapes and geometries have been specified by experts on detectability, but no guidance on how changes (small or large) to the shape may affect detectability has been provided. Deter- mination of detectability is outside the scope of this project, so no guidance on interpretation of dome shape and geometry after exposure has been developed. Importance Multipliers While individual tests have been performed to evaluate a number of durability-related properties, the importance of each test result to the expected overall system performance varies. To assist in the interpretation of the test results, a relative importance factor for estimating the performance of the detectable warning systems may be assigned to each test method. Selection of an appropriate importance factor for each test result requires some level of subjective judgment from the user. This judgment should consider (1) the test method and its accuracy at simulating the anticipated deterioration mechanism and at predicting performance and (2) the sig- nificance of tested property relative to the anticipated service environment. The importance can be judged to be low, medium, or high and these qualitative assignments have been quantified as importance multipliers equal to 1, 2, and 3, respectively. If a particular test is considered to be not applicable for a given agency, its test results can be left out of the analysis. Combination The method proposed for generating an overall rating is based on a well-established experimental methodology (Derringer and Suich, 1980). Mathematically, the overall rating is calculated as the geometric mean of the individual ratings for each of the tests. In general, for n test methods, the over- all rating is the nth root of the product of the ratings in each of those tests. For example, suppose that the ratings for three different (but equally important) tests are represented by r1, r2, and r3. The overall rating (R) is then determined according to . Since the individual ratings range between 0 and 4, the overall ratings also range between 0 and 4. The main reason for using a geometric mean instead of the more routine arithmetic mean (or average) is that if a system scores a 0 in any single test, which means that performance is likely to be unacceptable in that category, the overall rating is also 0. An unacceptable rating for any test implies that the product is unsuitable for use. This would not be the case if the arithmetic mean was used. In developing the rating correlation tables, it is important to consider this consequence of using the geometric mean; a 0 should be assigned only to test responses judged to be sufficiently far below desired performance that, on their own, they eliminate the tested product from further consideration. The importance of each test result may be considered in the calculation of the overall rating by including the result of that test in the calculation once, twice or three times if that method’s importance was judged to be low, medium or high, respectively, by assigning an importance multiplier of 1, 2, or 3. Example An example of an overall rating calculation for five hypo- thetical products is shown in Table 9. The exposure category R r r r= × ×1 2 3 3 24 Test Multiplier (Importance factor) Pr od uc t A Pr od uc t B Pr od uc t C Pr od uc t D Pr od uc t E Visual and Microscopic Evaluation 2 (M) 2 2 2 2 2 Color Measurement 1 (L) 1 2 2 1 3 Dome Shape and Geometry Measurement 2 (M) 2 3 2 2 2 Coating and Single Dome Bond 2 (M) 2 1 2 2 2 Slip Resistance 3 (H) 2 3 2 1 0 Resistance to Impact from Simulated Snowplow Blade 3 (H) 2 3 2 2 2 Resistance to Impact from Falling Tup 3 (H) 4 2 1 1 2 Wear Resistance 3 (H) 2 2 2 1 4 Overall Rating (Weighted geometric mean) 2.15 2.21 1.79 1.39 0.00 Table 9. Overall rating for five hypothetical products.

and importance factors have been selected to represent an urban, high-traffic setting in an environment where freezing and thawing is expected. While Table 9 shows a hypothetical set of results, the follow- ing discussion provides an example of how such results might be interpreted. For this example, both Products A and B are shown with similar overall ratings, and the difference in the overall rating between the two should not be considered sig- nificant. Differentiation of the performance between the two should be made based on the importance of individual tested properties, such as resistance to impact from falling tup. In contrast, the difference in overall rating assigned to Products C and D compared to Products A and B are large enough that their performance would be anticipated to noticeably lag that of Products A and B. Finally, while Product E appears to have performed well enough in most tests to achieve a rating of 2 or higher, a rating of 0 in slip resistance would produce an overall rating of 0. Such a rating would be representative of very poor performance and might indicate a tile that was too slippery to support pedestrian traffic. Obviously, such a situation must be avoided, and an overall rating of 0 is appropriate. Application of Test Protocol This test protocol was developed for use in comparing the performance of detectable warning systems. It is clear that each agency will want to consider different environmental and service conditions and will likely have access to only a subset of the products that are available nationwide. However, a primary objective of this development process was a universally appli- cable set of methods that would provide sufficient, objective, and valuable information to allow the test protocol results to be interpreted relative to the needs of each agency. To allow each agency to consider their own needs, the inter- pretation of the test results for a given product should be modified to suit the intended application. Note that this should not require modification of the test protocol itself. If the proposed rating and combination system was adopted, the interpretation could be modified by adjusting the ratings assigned to each result and the importance multipliers. The rating schemes were not included in the test methods, but provided separately, to allow individual agencies latitude to adopt ratings suitable for their application and particular needs. Furthermore, it is possible that a different method for com- bining test results could also be adopted to better suit a given set of circumstances. It is envisioned that raw test results obtained during testing programs conducted at the direction of material suppliers could be shared among multiple agencies. However, for the test data to have universal application, the test protocols must be strictly reproduced. In this way, all parties concerned will have a clear understanding of how the testing was performed and may form interpretations about how a given product may perform in the field based on their experience with similar products. In addition, data from products from different suppliers or even different generations of the same product can be compared. Two exposure categories have been developed to represent hot and cold environmental conditions, and these categories have been incorporated into the protocol. While additional exposure categories could be envisioned, for example a category based on traffic levels, the effort involved in executing this test protocol for even one category is significant. The decision to limit this protocol to only two categories was made to keep the effort required to reasonable limits. The rigorousness of the exposure regimes was designed to be more rather than less severe with the idea that if a product performs well in a severe test then it will do well in a milder one. In the application of this test protocol, the agency will need to decide whether the hot or cold category represents conditions in its state or municipality. It is likely that some agencies will need to consider both cate- gories in order for the conditions in their jurisdiction to be comprehensively represented. While the overall rating scheme has been adopted from a methodology targeted at optimizing performance, specifying agencies would probably prefer to be able to identify multiple products deemed likely to produce acceptable performance. Such products could be identified using this framework by defining a minimum acceptable overall rating that the performance must exceed. The correlation between test results and ratings will likely need to be revisited relative to this objective. 25

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TRB’s National Cooperative Highway Research Program (NCHRP) Report 670: Recommended Procedures for Testing and Evaluating Detectable Warning Systems explores a set of recommended test methods for evaluating the durability of detectable warning systems. These methods address exposure regimes, test procedures, and evaluation criteria to help select detectable warning systems that provide long-term performance and durability while meeting the requirements of the Americans with Disabilities Act Accessibility Guidelines.

The appendix contained in the research agency’s final report provides further elaboration on the work performed in this project. This appendix titled Research Leading to the Development of Methodology for Durability Assessment of Detectable Warning Systems is available online.

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