Guide for Pavement Friction (2009)

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C-1 APPENDIX C SUMMARY OF STATE FRICTION SURVEY RESPONSES

C-2 INTRODUCTION This appendix summarizes the responses provided by state highway agencies that participated in the pavement friction survey conducted in August 2003. PROCEDURES AND EQUIPMENT USED TO MEASURE PAVEMENT SURFACE CHARACTERISTICS Pavement Friction Test Protocol/Procedure Forty-one of the 45 responding agencies indicated using ASTM E 274 (“Test Method for Skid Resistance of Paved Surfaces Using a Full-Scale Tire”) as the principal protocol for performing pavement surface friction measurements. Arizona uses a test method that corresponds to the modified Dynatest Runway Friction Tester (herein termed Highway Friction Tester) it uses. Vermont, Delaware, and New Hampshire indicated that pavement friction is not measured in the field. Test Equipment ASTM E 274 measures the steady-state friction force between a specified full-scale automotive tire and a pavement surface using a locked test wheel as it is dragged over a the wetted pavement surface under constant load and at a constant speed, while its major plane is parallel to its direction of motion and perpendicular to the pavement. All 41 agencies reporting use of the ASTM E 274 test method use the skid trailer equipment specified by the method. Automotive Tire Type Used in Testing ASTM E 274 specifies two full-scale automotive tire types (ribbed and smooth tires) that can be used in testing as follows: • ASTM E 501 (“Standard Specification for Standard Rib Tire for Pavement Skid- Resistance Tests”). • ASTM E 524 (“Standard Specification for Standard Smooth Tire for Pavement Skid- Resistance Tests”). Table C-1 summarizes test tires used by the 41 agencies that employ the ASTM E 274. As can be seen, 23 of the 41 agencies use the ribbed tire exclusively, while 12 use both smooth and ribbed tires and the remaining six agencies use only smooth tires. The comments provided as part of responses indicate that the ribbed tire is generally used for network- level testing, while the smooth tire is used for testing in specific situations, such as crash investigations and research.

C-3 Table C-1. Test tires used as part of ASTM E 274 pavement surface friction testing. Agency Smooth Tire Ribbed Tire Notes Alabama √ √ Alaska √ Arkansas √ California √ Colorado √ √ Connecticut √ √ Florida √ √ Smooth tire used on accident sites and for research. Georgia √ √ Hawaii √ Idaho √ Illinois √ √ Both tires used most of the time. Indiana √ Iowa √ Kansas √ √ Smooth tire used in research. Kentucky √ √ Louisiana √ √ Maryland √ Maine √ Michigan √ √ Smooth tire for investigations only. Ribbed tire for network-level testing. Minnesota √ √ Mississippi √ Missouri √ Montana √ Nebraska √ Nevada √ New Jersey √ New Mexico √ New York √ North Carolina √ Ohio √ Oklahoma √ Other types noted, but not specified. Oregon √ Pennsylvania √ √ Puerto Rico √ South Carolina √ Tennessee √ Texas √ Utah √ Virginia √ Washington √ West Virginia √

C-4 Frequency of Calibration of Test Equipment As seen in table C-2, there was a wide range of responses concerning the frequency of calibration of test equipment. The responses include both local calibrations of system components (force plate, water flow, etc.) and full system calibrations at statewide or regional calibration sites; the former typically done on a daily, weekly, or monthly basis and the latter done over a period of several months or years. Table C-2. Frequency of equipment calibrations. Testing Frequency Number of Agencies Prior to Each Test 8 Daily/Weekly 3 Monthly 11 Every 3 to 6 months 3 Yearly 21 Every 2 to 3 years 14 >3 years 1 Use of International Friction Index The survey inquiry regarding use of the International Friction Index (IFI) shows that only 4 of the 42 states that conduct friction testing—Iowa, Oklahoma, New Mexico, and West Virginia—use IFI to characterize pavement surface friction. Pavement–Tire Noise Table C-3 presents a summary of the test methods performed to characterize pavement–tire noise. The information in this table shows that slightly more than half (24) of the 45 responding states do not perform pavement–tire noise testing. Among those that perform noise testing outside of the research realm, pass-by measurement techniques are more commonly used than near-tire techniques. Additionally, fewer agencies measure interior noise, as compared to exterior noise.

C-5 Table C-3. Summary of test methods performed to characterize pavement–tire noise. Agency Pass-By Measurements of Total Traffic Flow Pass-By Measurements of Individual Vehicles Vehicle Interior Measurements Near-Tire Measurements in Field Near-Tire Measurements in Lab NCAT Noise Trailer None Notes Alabama √ Alaska √ Arizona √ √ √ √ Arkansas √ California √ √ √ Colorado √ √ √ √ Connecticut √ Delaware √ Florida √ Georgia √ Hawaii √ Idaho √ Most measurements have been individual qualitative observations in urban areas. Plan to be more involved in noise measurement. Illinois √ Indiana √ Iowa √ √ Kansas √ √ Kentucky Done by Kentucky Transportation Research Center on individual projects. Louisiana √ √ Research applications only; using pass-by measurements of total traffic flow and individual vehicles. Maryland Office of Env. Design is responsible for noise measurements. Maine √ Michigan √ √ √ √

C-6 Table C-4. Summary of test methods performed to characterize pavement–tire noise (continued). Agency Pass-By Measurements of Total Traffic Flow Pass-By Measurements of Individual Vehicles Vehicle Interior Measurements Near-Tire Measurements in Field Near-Tire Measurements in Lab NCAT Noise Trailer None Notes Minnesota √ √ √ Participated in Marquette University Noise & Texture in PCC Pavements study. Mississippi √ Missouri √ Montana √ Nebraska √ Nevada √ √ NCAT is performing near-tire measurements for NDOT in Las Vegas on different pavement types and textures. No report yet. New Hampshire √ New Jersey √ New Mexico √ New York √ North Carolina √ Ohio √ Oklahoma √ Oregon √ Pennsylvania √ Puerto Rico √ South Carolina √ Tennessee √ Texas √ √ √ Utah √ Vermont √ Virginia √ Washington √ West Virginia √

C-7 Pavement Surface Texture Test Methods Table C-4 summarizes test methods used by the 45 responding agencies to characterize pavement surface texture. The table shows that about half (23) of the states do not conduct surface texture tests. The remaining states typically use one test method, the most common being the sand patch and British Pendulum Tests. Five states—Louisiana, Michigan, Missouri, New Jersey, and Texas—use two or more methods to measure pavement surface texture. Table C-4. Summary of test methods used to characterize pavement surface texture. Test Method Number of Agencies Grease Sample 0 Sand Patch 15 Outflow Meter 4 British Pendulum Tester 8 Laser Device 2 None 23 Frequency of Pavement Surface Texture Testing A summary of the information obtained on pavement surface texture testing frequency is presented in table C-5. Examination of this table shows that texture testing is not a regular occurrence in most states, and its adoption as part of pavement evaluation/management is still in its infant stages. The vast majority of states do not perform texture testing or only test texture for research purposes. Only Minnesota and New Jersey reported doing texture testing on a regular basis, while Colorado, Georgia, and Montana indicated testing at time of construction.

C-8 Table C-5. Frequency of pavement surface texture testing. Testing Frequency Agency Never Yearly Every Other Year Every 5 years Research Only At Construction Notes Alabama √ Alaska √ Arizona √ Arkansas √ California √ Colorado √ √ For acceptance of Astroturf drag. Connecticut √ Delaware √ Florida √ Georgia √ Hawaii √ Idaho √ Illinois √ Indiana √ Iowa √ Kansas √ Kentucky √ Louisiana √ Maryland √ Maine √ Michigan √ Next year, test on 3-year cycle. Minnesota √ Mississippi √ Testing sometimes done to meet shotblasting specifications. Missouri √ Montana √ Nebraska √ Nevada √ New Hampshire √ New Jersey √ New Mexico √ New York √ North Carolina √ Ohio √ Oklahoma √ Oregon √ Pennsylvania √ Puerto Rico √ South Carolina √ Tennessee √ Texas √ Utah √ Vermont √ Virginia √ Washington √ West Virginia √

C-9 DESIGN AND CONSTRUCTION STANDARDS FOR ENSURING HIGH-FRICTION, LOW- NOISE PAVEMENTS (NEW AND RESTORED) Pavement Friction Aggregate Properties and Tests The vast majority of states (41 of 45) indicate that they specify and test for aggregate properties as part of their pavement friction design process. The properties and tests reported range from basic physical features of the aggregate, such as size, gradation, and shape, to the evaluation of durability and soundness to detailed assessment of frictional characteristics. The tests include an array of national and state standardized procedures, with many of the state tests being modified versions of the following AASHTO and ASTM standards: • AASHTO T 11 (ASTM C 117)—“Materials Finer Than No. 200 (75 μm) Sieve in Mineral Aggregates by Washing.” • AASHTO T 27 (ASTM C 136)—“Sieve Analysis of Fine and Coarse Aggregates.” • AASHTO TP 58—“Resistance of Coarse Aggregate to Degradation by Abrasion in the Micro-Deval Apparatus.” • AASHTO T 85 (ASTM C 127)—“Specific Gravity and Absorption of Coarse Aggregate.” • AASHTO T 96—“Resistance to Degradation of Small-Size Coarse Aggregate by Abrasion and Impact in the Los Angeles Machine.” • AASHTO T 103—“Soundness of Aggregates by Freezing and Thawing.” • AASHTO T 104—“Soundness of Aggregate by Use of Sodium Sulfate or Magnesium Sulfate.” • AASHTO TP 33 / T 304 (ASTM C 1252)—“Uncompacted Void Content of Fine Aggregate (as Influenced by Particle Shape, Surface Texture and Grading).” • ASTM D 3042—“Acid Insoluble Residue in Carbonate Aggregate.” • ASTM C 295/C 296: “Petrographic Examination of Aggregates for Concrete.” • ASTM D 4791—“Flat Particles, Elongated Particles, or Flat and Elongated Particles in Coarse Aggregate.” • ASTM D 5821—“Percentage of Fractured Particles in Coarse Aggregate.” • Atterberg limits. • AASHTO T 89—“Determining the Liquid Limit of Soils.” • AASHTO T 90—“Plastic Limit and Plasticity Index of Soils.” Table C-6 provides a breakdown of the number of states that specify and test for those aggregate properties believed to affect pavement friction. The properties include those that are important to other aspects of pavement design, such as mix stability and strength, as well as those specifically related to pavement friction, such as polish value determined via the British Pendulum Tester.

C-10 Table C-6. Summary of test properties used in aggregate selection. Aggregate Property No. of States Gradation and Size 8 Angularity, Shape, and Texture 16 Mineral Composition 15 Resistance to Degradation and Abrasion 21 Durability and Soundness 11 Polish and Frictional Characteristics 11 As can be seen, the properties reported by most states were resistance to degradation and abrasion (e.g., LA Abrasion loss), followed by angularity, shape, and texture (e.g., crushed particles, fractured faces, flat and elongated pieces), and mineral composition (e.g., limestone, silica content). Durability and soundness (e.g., sulfate or freeze-thaw soundness) and polish and frictional characteristics (e.g., polish value, acid insoluble residue) also were noted by several states. Guidelines for Maintaining Pavement Surface Friction Agencies generally ensure pavement surface friction by specifying pavement surface material (AC or PCC) mix properties or pavement surface texture. A detailed summary of current specifications used by states for pavement surface texture is presented later in this chapter. Summaries of the surface material requirements and finishing specifications are presented in table C-7. The information in this table shows that agencies typically use a combination of material properties and surface finishing methods to ensure adequate levels pavement surface friction. Material specifications include the use of specific types of AC mixture types, aggregate types, aggregate size, gradation, shape, and aggregate polish value. Finishing requirements are basically specifications for pavement surface texture. Agency Methods for PCC Finishing/Texturing For PCC-surfaced pavements, agencies specify pavement surface texture properties to ensure pavement friction. Pavement surface texture specifications reported as part of this survey are summarized in table C-8.

C-11 Table C-7. Summary of the surface material requirements and finishing specifications. Agency Use of Specific Aggregate Types Surface Texture Requirements Aggregate Size, Gradation, Shape Aggregate Polish Value Mix Type (for AC) Use of Additives and Rubber (for AC) Surface Finishing (for PCC) Alabama √ √ √ √ √ √ Alaska Arizona √ √ √ Arkansas √ √ √ California √ √ √ Colorado √ √ √ √ Connecticut √ √ √ Delaware √ √ √ √ √ √ Florida √ √ √ √ √ √ Georgia √ √ √ √ √ Hawaii √ √ √ Idaho √ √ √ Illinois √ √ Indiana √ √ √ √ Iowa √ √ √ √ √ Kansas √ √ √ √ Kentucky √ √ √ √ √ √ √ Louisiana √ √ √ √ Maine √ √ √ √ Maryland √ √ √ √ Michigan √ √ √ √ √ Minnesota √ √ Mississippi √ √ √ Missouri √ √ Montana √ √ Nebraska √ Nevada √ New Hampshire √ New Jersey √ √ √ √ √ New Mexico √ √ √ √ √ √ New York √ √ √ √ √ North Carolina √ √ √ √ √ √ Ohio √ Oklahoma √ √ √ √ Oregon √ Pennsylvania √ √ Puerto Rico √ √ √ √ South Carolina √ √ √ √ √ Tennessee √ √ √ √ √ Texas √ √ Utah √ √ √ √ √ √ Vermont √ √ √ Virginia √ Washington √ √ √ √ West Virginia √ √ √

C-12 Table C-8. Agency methods for PCC finishing/texturing. Texturing Method Agency Tining Grooving Burlap Grinding Astroturf drag Sawcutting Alabama √ √ Alaska √ Arizona √ Arkansas √ √ California √ √ √ Colorado √ √ Connecticut √ √ √ √ Delaware √ √ √ √ Florida √ Georgia √ √ √ Hawaii √ √ √ Idaho √ Illinois √ √ √ √ Indiana √ √ Iowa √ √ Kansas √ √ √ Kentucky √ √ √ Louisiana √ √ √ Maine a Maryland √ √ √ Michigan √ √ √ √ Minnesota √ Mississippi √ Missouri √ √ √ Montana √ √ Nebraska √ Nevada √ √ √ New Hampshire √ √ New Jersey √ √ New Mexico √ √ New York √ √ √ √ North Carolina √ Ohio √ Oklahoma √ Oregon √ Pennsylvania √ √ Puerto Rico √ √ √ South Carolina √ √ Tennessee √ √ √ Texas √ Utah √ Vermont a Virginia √ √ √ Washington √ West Virginia √ a State does not pave with PCC.

C-13 This table shows that 37 of the 45 agencies specify tining as a finishing method for new PCC surfaces. Twenty-one states specify burlap or Astroturf drag techniques, mostly in conjunction with tining, while 25 states use grooving or grinding on either new or existing PCC pavement. Twenty-six of the 37 agencies that require tining, specify that it be done transversely (i.e., perpendicular to centerline), whereas six states—Arizona, California, Colorado, Florida, Nebraska, and Nevada—specify longitudinal tining. Iowa and New York allow both longitudinal and transverse tining, while Virginia allows transverse and crisscross (transverse and longitudinal combined) tining. Dimensions of tining grooves range primarily from 0.08 to 0.25 in (2 to 6 mm) deep and 0.06 to 0.125 in (1.5 to 3 mm) wide, and the spacing of the grooves range from 0.5 to 1.0 in (12 to 25 mm). Randomly spaced grooves typically vary from 0.25 to 1.5 in (6 to 38 mm). Agency Practices Concerning Triggers for Friction Restoration Highway agencies take varied approaches toward identifying friction deficiencies and establishing solutions for restoring friction. Some agencies, such as New Hampshire and Vermont, do not monitor friction levels but periodically examine crash rates and/or certain distress types (e.g., rutting, drainage issues) that might warrant friction-related treatments. Some states perform friction testing in response to requests from Districts or other departments concerned with higher-than-normal crash rates. For instance, the Ohio DOT evaluates pavements on a site-by-site basis as identified by District, Project, or Construction Engineers, or by wet crash data. The most common approach of determining friction deficiency involves a combination of network-level friction monitoring and crash rate evaluation. In this approach, the statewide system of highways is tested for friction on a 1-, 2-, or 3-year basis and the results are reviewed to identify any potentially deficient locations. Such locations are generally flagged using a specific trigger friction value, and those locations are then cross-checked with crash data simultaneously maintained and analyzed. Depending on the results, the agency may choose a variety of responses, from doing nothing to conducting an on-site evaluation of the subject location to taking preliminary safety precautions (e.g., erecting signs, initiating plans for treatment in the future) to enacting immediate safety measures (e.g., restoration treatment). Although some states use their trigger friction value as a means of initiating some sort of restoration treatment, many use it to prompt a detailed project-level investigation of friction. Nevertheless, it is of some interest to examine the trigger values that are used and the nature of the friction index used. Table C-9 provides a summary of the trigger friction values reported in the state surveys.

C-14 Table C-9. Trigger values used in identifying potential friction-deficient locations. Number of States Friction Value Ribbed-Tire Friction Number (FNR) Smooth-Tire Friction Number (FNS) Highway Friction Tester (HFT) <37 2 <35 5 1 1 <32 1 <30 6 <25 1 ≤20 3 Techniques Used to Maintain Friction The treatments that agencies use to restore pavement surface friction are summarized in table C-10. As can be seen, the most common treatments consist of thin AC overlays, PCC grinding, and micro-surfacing. Other types of treatments reportedly used include chip seals and PCC surface retexturing, in the form of shot-blasting or grooving. Pavement–Tire Noise Pavement–Tire Noise Considerations in AC- and PCC-Surfaced Pavement Design Only 10 of the 45 responding states directly consider the effect of pavement–tire noise in the design of AC-surfaced pavements—Arizona, Colorado, Kentucky, Michigan, Nevada, New Jersey, New Mexico, Oregon, Texas, and Utah. Among these states, open-graded asphalt, stone matrix asphalt (SMA), and rubberized asphalt mixes are most commonly used to reduce pavement–tire noise. As seen in table C-11, 16 of the 45 responding agencies consider the effects of noise when specifying surface texture for PCC pavements. The most common forms of texturing for noise reduction include random tining, diamond grinding, and longitudinal tining.

C-15 Table C-10. Summary of treatments used to restore pavement surface friction. Treatment Types Agency Grinding Thin Overlays Micro- surfacing Shotblasting Grooving Milling Scarifying Chip Seals Alabama √ √ √ Alaska Arizona √ √ √ √ Arkansas √ √ b California √ √ Colorado √ √ √ √ a Connecticut √ √ √ Delaware Florida √ Georgia √ √ √ Hawaii √ Idaho √ √ √ Illinois √ √ √ Indiana √ √ √ Iowa √ √ Kansas √ √ Kentucky √ √ Louisiana √ √ √ Maine √ √ √ Maryland √ √ √ Michigan √ √ √ √ √ Minnesota √ √ √ Mississippi √ √ √ √ √ √ Missouri √ √ √ Montana √ Nebraska √ b Nevada √ √ New Hampshire √ New Jersey √ √ √ New Mexico √ √ √ New York √ √ √ North Carolina √ √ √ Ohio √ √ √ Oklahoma √ √ √ √ Oregon √ √ Pennsylvania √ √ √ √ Puerto Rico √ √ South Carolina √ Tennessee √ b √ √ Texas √ b √ √ Utah √ √ √ √ Vermont √ √ Virginia √ √ Washington West Virginia √ a Chip seals on low-volume roadways. b Others reported, but not specified.

C-16 Table C-11. Textures specified for noise in PCC design. Finishing Method Agency Random Tining Burlap Drag Grooving Grinding Long. Tining Astroturf Drag Notes Alabama None. Alaska None. Arizona Other: Open-graded AC mix Arkansas None. California None. Colorado √ √ Astroturf drag for posted speeds<45 mi/hr (<72 km/hr). Connecticut None. Delaware None. Florida None. Georgia None. Hawaii √ Idaho None. Illinois None. Indiana None. Iowa √ √ √ Kansas √ √ Kentucky √ √ Louisiana None. Maine None. Maryland None. Michigan √ √ √ Grinding as mitigation. Minnesota √ Mississippi None. Missouri None. Montana None. Nebraska None. Nevada √ New Hampshire None. New Jersey √ New Mexico √ New York √ North Carolina √ √ Ohio None. Oklahoma None. Oregon √ Pennsylvania None. Puerto Rico √ South Carolina None. Tennessee None. Texas √ Utah √ Vermont Not applicable. Virginia None. Washington None. West Virginia None.

C-17 SAFETY AND LEGAL ISSUES RELATED TO FRICTION/TEXTURE AND CRASH RATES Agency Practices Relating Friction to Crashes Although several states compare wet-weather crash rates with friction test results to determine if a site needs remedial action, only a few have investigated the relationship on a broad scale. Texas and North Carolina reported finding no direct correlation between friction and crashes. Arizona noted that, “research by others has indicated a friction value of 35 reflects accident breakpoint.” California noted that “a CALTRANS study found that there was a relationship between FN<25 and a high frequency of accidents.”