Module 2-4Module 2-4

Roughness and Roughness and Surface Friction TestingSurface Friction Testing

Learning ObjectivesLearning Objectives Explain the importance of conducting Explain the importance of conducting

roughness and surface friction evaluationsroughness and surface friction evaluations Describe the different types of roughness Describe the different types of roughness

survey methods, equipment types, and survey methods, equipment types, and roughness indicesroughness indices

Describe the different types of friction Describe the different types of friction measuring equipmentmeasuring equipment

List the different categories of surface List the different categories of surface texturetexture

Learning Objectives Learning Objectives (continued)(continued)

Explain the importance of measuring Explain the importance of measuring surface texture as part of a surface friction surface texture as part of a surface friction evaluationevaluation

Describe the different types of texture-Describe the different types of texture-measuring devicesmeasuring devices

Explain the advantages of using IRI and IFI Explain the advantages of using IRI and IFI over other indicesover other indices

Describe how roughness- and friction-Describe how roughness- and friction-related information influences the selection related information influences the selection of rehabilitation activitiesof rehabilitation activities

Why is it important to assess Why is it important to assess roughness and friction?roughness and friction?

Both affect “functional” performanceBoth affect “functional” performance

Roughness leads to increases in: Roughness leads to increases in: Vehicle operating costsVehicle operating costs User delayUser delay AccidentsAccidents User dissatisfactionUser dissatisfaction

Friction loss leads to increases in wet Friction loss leads to increases in wet weather accidentsweather accidents

Roughness SurveysRoughness Surveys

Definition of RoughnessDefinition of Roughness Deviations in pavement surface that affect Deviations in pavement surface that affect

ride qualityride quality

Caused by:Caused by: Built-in surface irregularitiesBuilt-in surface irregularities Traffic and environmentTraffic and environment

Purpose of a Purpose of a Roughness SurveyRoughness Survey

Identify areas of severe roughnessIdentify areas of severe roughness

Determine relative roughness between Determine relative roughness between projectsprojects

Gauge benefits of various rehabilitation Gauge benefits of various rehabilitation activities by measuring roughness before activities by measuring roughness before and after constructionand after construction

Roughness Survey TypesRoughness Survey Types

1.1.Ride quality surveys (serviceability)Ride quality surveys (serviceability) Subjective methodSubjective method Simple assessment toolSimple assessment tool

2.2.Objective roughness surveysObjective roughness surveys Quantitative unbiased methodQuantitative unbiased method Various types of equipment are Various types of equipment are

availableavailable

Ride Quality SurveysRide Quality SurveysServiceabilityServiceability

Subjective measure of user’s perception Subjective measure of user’s perception of pavement rideabilityof pavement rideability

Measurement scaleMeasurement scale Zero (very poor) to Five (very good)Zero (very poor) to Five (very good) Working range: 1.5 to 4.5Working range: 1.5 to 4.5

Trigger levels for rehabilitation depend on Trigger levels for rehabilitation depend on speed and level of trafficspeed and level of traffic

Correlations with other roughness indicesCorrelations with other roughness indices

Roughness Measuring Roughness Measuring EquipmentEquipment

Response-Type Road Roughness Response-Type Road Roughness Measuring Systems (RTRRMS)Measuring Systems (RTRRMS) MaysmeterMaysmeter PCA RoadmeterPCA Roadmeter BPR RoughometerBPR Roughometer

Inertial Road Profiling Systems (IRPS)Inertial Road Profiling Systems (IRPS) ICC ProfilerICC Profiler K.J. Law ProfilometerK.J. Law Profilometer South Dakota ProfilerSouth Dakota Profiler

Response-Type Road Response-Type Road Roughness Measuring Systems Roughness Measuring Systems

(RTRRMS)(RTRRMS) Measure vehicle responseMeasure vehicle response AdvantagesAdvantages

Low initial and operating costsLow initial and operating costs Ease of operationEase of operation High measuring speedsHigh measuring speeds

DisadvantagesDisadvantages Output sensitive to vehicle Output sensitive to vehicle

characteristicscharacteristics Requires frequent calibrationRequires frequent calibration

Response-Type SystemsResponse-Type SystemsMaysmeter Maysmeter

Inertial Road Profiling Inertial Road Profiling Systems Equipment (IRPS)Systems Equipment (IRPS)

Measure actual pavement profileMeasure actual pavement profile AdvantagesAdvantages

Relatively accurate and repeatable Relatively accurate and repeatable profile measurementsprofile measurements

Used to calibrate RTRRM systemsUsed to calibrate RTRRM systems DisadvantagesDisadvantages

High capital and operating expensesHigh capital and operating expenses Complexity of systemsComplexity of systems

Inertial Profiler SystemsInertial Profiler Systems

International Roughness International Roughness Index (IRI)Index (IRI)

Current roughness measurement standardCurrent roughness measurement standard

Correlates to RTRRM systemsCorrelates to RTRRM systems

Scale: 0 to 20 m/km (0 to 1267 in/mi)Scale: 0 to 20 m/km (0 to 1267 in/mi)

2 m/km (125 in/mi) is typical break point 2 m/km (125 in/mi) is typical break point between between roughrough and and smoothsmooth pavements pavements

Standard for FHWA HPMS DatabaseStandard for FHWA HPMS Database

Roughness Data VariabilityRoughness Data Variability

Seasonal and daily environmental effectsSeasonal and daily environmental effects

Lateral positioningLateral positioning

Differences in operator practice (between-Differences in operator practice (between-operator variability)operator variability)

Differences between equipment devices Differences between equipment devices (between-device variability)(between-device variability) Manufacturing differencesManufacturing differences Calibration problemsCalibration problems

Surface Friction TestingSurface Friction Testing

Definition ofDefinition ofSurface FrictionSurface Friction

Force developed at pavement-tire Force developed at pavement-tire interface that resists slidinginterface that resists sliding

Influenced by:Influenced by: Surface textureSurface texture Surface drainage (cross-slope)Surface drainage (cross-slope)

Purpose of a Surface Purpose of a Surface Friction SurveyFriction Survey

Assess safety concernsAssess safety concerns HydroplaningHydroplaning Wet weather accidentsWet weather accidents

Target testing in areas of poor surface Target testing in areas of poor surface condition:condition: Smooth macrotexture (polishing or Smooth macrotexture (polishing or

inadequate finishing)inadequate finishing) Inadequate pavement cross slopeInadequate pavement cross slope

How do you adequately assess How do you adequately assess surface frictional characteristics? surface frictional characteristics?

Historical methodHistorical method——Measure friction Measure friction directly (“skid number”)directly (“skid number”)

Recent research indicates that “surface Recent research indicates that “surface texture” MUST also be consideredtexture” MUST also be considered

What is surface texture?What is surface texture? Characteristics that contribute to surface Characteristics that contribute to surface

frictionfriction Microtexture – Roughness of individual Microtexture – Roughness of individual

pieces of aggregatepieces of aggregate MacrotextureMacrotexture

General coarseness of pavement surfaceGeneral coarseness of pavement surface Formed water channels (grooving)Formed water channels (grooving) Large impact on surface frictionLarge impact on surface friction

Friction Survey Measurement Friction Survey Measurement Equipment TypesEquipment Types

Locked-wheel testersLocked-wheel testers

Side force testers (Mu Meter, SCRIM)Side force testers (Mu Meter, SCRIM)

Fixed slip testers (Gripster)Fixed slip testers (Gripster)

Variable slip testers (Norsemeter ROAR)Variable slip testers (Norsemeter ROAR)

Note: These devices do NOT measure texture!Note: These devices do NOT measure texture!

Friction Measuring DevicesFriction Measuring DevicesLocked-Wheel TrailerLocked-Wheel Trailer

Friction Measuring DevicesFriction Measuring DevicesExamples of Other DevicesExamples of Other Devices

Mu MeterMu Meter(side force tester)(side force tester)

SCRIMSCRIM(side force tester)(side force tester)

Norsemeter ROARNorsemeter ROAR(variable slip tester)(variable slip tester)

Surface Texture Measuring Surface Texture Measuring DevicesDevices

Volumetric (“Sand Patch”) methodVolumetric (“Sand Patch”) method

Outflow meterOutflow meter

Circular track meter (CTMeter)Circular track meter (CTMeter)

High-speed laser-based devices High-speed laser-based devices (ROSAN, most laser-based profilers)(ROSAN, most laser-based profilers)

Surface Texture MeasurementSurface Texture MeasurementSand Patch MethodSand Patch Method

Surface Texture MeasurementSurface Texture MeasurementHigh-speed Laser-Based DevicesHigh-speed Laser-Based Devices

ROSANvROSANv

High-Speed Inertial High-Speed Inertial ProfilersProfilers

International Friction Index International Friction Index (IFI)(IFI)

Incorporates simultaneous measurements Incorporates simultaneous measurements of friction and macrotextureof friction and macrotexture Speed constant (SSpeed constant (Spp)) Friction number (F60)Friction number (F60)

Becoming friction measurement standardBecoming friction measurement standard Modern high-speed measuring equipment Modern high-speed measuring equipment

measure IFI directlymeasure IFI directly

ReviewReview Why is it important to conduct roughness Why is it important to conduct roughness

and surface friction evaluations?and surface friction evaluations? What are the two types of roughness What are the two types of roughness

measuring equipment? measuring equipment? What are two types of friction measuring What are two types of friction measuring

equipment?equipment? What are the three categories of surface What are the three categories of surface

texture?texture?

Review (continued)Review (continued) Why it is important to measure surface Why it is important to measure surface

texture as part of a surface friction texture as part of a surface friction evaluation?evaluation?

What are two of the different types of What are two of the different types of texture-measuring devices?texture-measuring devices?

What are the advantages of using IRI and What are the advantages of using IRI and IFI (over other indices)?IFI (over other indices)?

How do roughness and friction affect the How do roughness and friction affect the selection of rehabilitation alternatives?selection of rehabilitation alternatives?

Henry, J. J. 2000. Henry, J. J. 2000. Evaluation of Pavement Friction Evaluation of Pavement Friction CharacteristicsCharacteristics. Synthesis of Highway Practice No. 291. . Synthesis of Highway Practice No. 291. National Cooperative Highway Research Program, National Cooperative Highway Research Program, Transportation Research Board, Washington, DC.Transportation Research Board, Washington, DC.

Karamihas, S. M., T. D. Gillespie, R. W. Perera, and S. D. Karamihas, S. M., T. D. Gillespie, R. W. Perera, and S. D. Kohn. 1999. “Guidelines for Longitudinal Pavement Kohn. 1999. “Guidelines for Longitudinal Pavement Profile Measurement.” Profile Measurement.” NCHRP Report 434NCHRP Report 434. . Transportation Research Board, Washington, DC.Transportation Research Board, Washington, DC.

Ksaibati, K., R. McNamara, W. Miley, and J. Armaghani. Ksaibati, K., R. McNamara, W. Miley, and J. Armaghani. 1999. “Pavement Roughness Data Collection and 1999. “Pavement Roughness Data Collection and Utilization.” Utilization.” Transportation Research Record 1655Transportation Research Record 1655. . Transportation Research Board, Washington, DC.Transportation Research Board, Washington, DC.

Key ReferencesKey References

Sayers, M. W. and S. M. Karamihas. 1998. Sayers, M. W. and S. M. Karamihas. 1998. The Little The Little Book of Profiling—Basic Information about Measuring and Book of Profiling—Basic Information about Measuring and Interpreting Road ProfilesInterpreting Road Profiles. University of Michigan . University of Michigan Transportation Research Institute, Ann Arbor, MI. Web Transportation Research Institute, Ann Arbor, MI. Web address: www.umtri.umich.edu/erd/roughness.address: www.umtri.umich.edu/erd/roughness.

Smith, K. L., K. D. Smith, L. D. Evans, T. E. Hoerner, and Smith, K. L., K. D. Smith, L. D. Evans, T. E. Hoerner, and M. I. Darter. 1997. “Smoothness Specifications for M. I. Darter. 1997. “Smoothness Specifications for Pavements.” Web Document #1, Final Report NCHRP Pavements.” Web Document #1, Final Report NCHRP Project 1-31. Transportation Research Board, Project 1-31. Transportation Research Board, Washington, DC. Washington, DC.

Key References Key References (continued)(continued)

ASTM E 274, ASTM E 274, Skid Resistance of Pavements Using a Full-Skid Resistance of Pavements Using a Full-Scale TireScale Tire

ASTM E 965, ASTM E 965, Measuring Pavement Macrotexture Depth Measuring Pavement Macrotexture Depth Using a Volumetric TechniqueUsing a Volumetric Technique

ASTM E 1845, ASTM E 1845, Calculating Pavement Macrotexture Profile Calculating Pavement Macrotexture Profile DepthDepth

ASTM E 1859, ASTM E 1859, Friction Coefficient Measurements Friction Coefficient Measurements Between Tire and Pavement Using a Variable Slip Between Tire and Pavement Using a Variable Slip TechniqueTechnique

ASTM E 1926, ASTM E 1926, Calculating International Roughness Index Calculating International Roughness Index of a Pavement Surfaceof a Pavement Surface

ASTM E 1960, ASTM E 1960, Calculating International Friction Index of a Calculating International Friction Index of a Pavement SurfacePavement Surface

Applicable ASTM Applicable ASTM StandardsStandards