National Highway Institute 4-1 REV-2, JAN 2006 PROFILE INDICES BLOCK 4

National Highway Institute 4-2 REV-2, JAN 2006 Objectives l Introduce different types of profile indices l Describe International Roughness Index and Ride Number l Describe Profile Index computed from profilograph trace

National Highway Institute 4-3 REV-2, JAN 2006 International Roughness Index (IRI)

National Highway Institute 4-4 REV-2, JAN 2006 Background l In 1982 World Bank conducted an experiment in Brazil to establish a standard for roughness measurement l Resulted in development of IRI l States reporting roughness of HPMS sections in IRI since 1990

National Highway Institute 4-5 REV-2, JAN 2006 Background (Continued) l IRI is highly correlated to: –Vertical passenger acceleration (Ride Quality) –Tire Loads (vehicle control and safety) –Output from Response Type Roughness Measuring Systems

National Highway Institute 4-6 REV-2, JAN 2006 Properties of IRI Analysis l IRI computed using quarter car model

National Highway Institute 4-7 REV-2, JAN 2006 Properties of IRI Analysis (Continued) l Quarter-car modeled as: one tire, mass of axle supported by tire, suspension spring and damper, mass of the body supported by tire. l Simulation speed is 80 km/hr (50 mi/hr) l Suspension motion is accumulated (e.g., meters) and divided by distance traveled (e.g., kilometers) to give IRI (e.g., meters/kilometer)

National Highway Institute 4-8 REV-2, JAN 2006 Computation of IRI l Need a profile collected by an inertial profiler l Computation of IRI performed as specified in ASTM Standard E l Parameters of quarter car (e.g., spring stiffness etc) referred to as “Golden Car Parameters”

National Highway Institute 4-9 REV-2, JAN 2006 Road Profile and Wavelengths A road profile can be separated to different wavelengths

National Highway Institute 4-10 REV-2, JAN 2006 Road Profile and Wavelengths l Sum of waves creates profile l Profile is made up of unique set of wavelengths l Wavelengths determined using Fourier transform

National Highway Institute 4-11 REV-2, JAN 2006 Response of IRI to Wavelengths (Cont.) 1 ft = 0.3 m

National Highway Institute 4-12 REV-2, JAN 2006 Equipment Requirements for IRI l Resolution of height sensor 0.1 mm (0.004 in) or less. l Sample interval must be 167 mm (6.7 in) or less. l If profile data are sampled at 167 mm (6.7 in) or less and averaged before saving, recording interval must be 250 mm (10 in) or less

National Highway Institute 4-13 REV-2, JAN 2006 Advantages of IRI l Reproducible, portable and stable with time l General pavement condition indicator l Describes roughness that causes vehicle vibrations

National Highway Institute 4-14 REV-2, JAN 2006 Half Car Roughness Index (HRI)

National Highway Institute 4-15 REV-2, JAN 2006 Half Car Roughness Index (HRI) l For computation of HRI, profile data from left and right wheel paths are averaged l Then the IRI computation procedure is used on this “averaged” profile

National Highway Institute 4-16 REV-2, JAN 2006 Relationship Between IRI AND HRI 1 m/km = 63.4 in/mile

National Highway Institute 4-17 REV-2, JAN 2006 Ride Number (RN)

National Highway Institute 4-18 REV-2, JAN 2006 Background l RN is a index that rates rideability of a road on a scale from 0 to 5 (best) l RN is intended to match the mean panel rating of a rating panel l RN in ASTM Standard developed by University of Michigan Transportation Research Institute as part of FHWA project

National Highway Institute 4-19 REV-2, JAN 2006 Computation of RN l Need a profile collected by an inertial profiler l Computation of RN is performed by a computer program. Method specified in ASTM Standard E l RN is calculated for a single profile.

National Highway Institute 4-20 REV-2, JAN 2006 Computation of RN (Continued) l Uses quarter car model with different parameters from IRI l An index is calculated from the profile, and transformed to obtain RN, RN = 5e (-160PI) l For profilers that measure along both wheel paths, program computes mean RN. l Mean RN is not equal to average of left and right wheel path RN.

National Highway Institute 4-21 REV-2, JAN 2006 Response of RN to Wavelengths 1 ft = 0.3 m

National Highway Institute 4-22 REV-2, JAN 2006 Equipment Requirements for RN l Resolution of height sensor 0.1 mm (0.004 in) or less. l Sample interval must be 50 mm (2 in) or less. l If profile data are sampled at 50 mm (2 in) or less and averaged before saving, recording interval must be 75 mm (3 in) or less

National Highway Institute 4-23 REV-2, JAN 2006 Advantages of RN l Estimates Mean Panel Rating l Reproducible, portable, and stable over time

National Highway Institute 4-24 REV-2, JAN 2006 PROFILE INDEX (PI) FROM PROFILOGRAPH OUTPUT

National Highway Institute 4-25 REV-2, JAN 2006 Background of Profile Index (PI) l Measurements recorded by a profilograph are used to obtain the PI of the pavement l The PI is a measure of the smoothness of the roadway.

National Highway Institute 4-26 REV-2, JAN 2006 Determination of PI l Position blanking band on trace. Typically blanking band is 5 mm (0.2 inches) wide l Determine Profile Index (PI): Excursions that extend in height above blanking band are evaluated to compute PI

National Highway Institute 4-27 REV-2, JAN 2006 Determination of PI (continued) 1 ft = 0.3 m 1 in = 25.4 mm

National Highway Institute 4-28 REV-2, JAN 2006 Determination of PI (continued) 1 ft = 0.3 m 1 in = 25.4 mm

National Highway Institute 4-29 REV-2, JAN 2006 Determination of PI (Continued) l From Profilograph trace: –Performed manually by an operator –Profilograph trace digitized and computer program used to compute PI (Proscan) l Computerized Profilograph: PI computed using a computer program

National Highway Institute 4-30 REV-2, JAN 2006 Determination of PI (Continued) l Some States are using zero blanking bands as they have found a blanking band can hide pavement features that cause roughness

National Highway Institute 4-31 REV-2, JAN 2006 COMPARISON BETWEN PROFILE INDICES

National Highway Institute 4-32 REV-2, JAN 2006 PI VS PSI 1 ft = 0.3 m, 1 in = 25.4 mm, 1 in/mile = 0.02 m/km

National Highway Institute 4-33 REV-2, JAN 2006 PI vs IRI - 5 mm (0.2 in) Blanking Band - TTI 1 mm/m = 63.4 in/mile

National Highway Institute 4-34 REV-2, JAN 2006 PI vs IRI (Zero Blanking Band) - TTI 1 mm/m = 63.4 in/mile

National Highway Institute 4-35 REV-2, JAN 2006 IRI vs. Simulated PI for AC Pavements 5-mm Blanking Band 2.5-mm Blanking Band Zero Blanking Band 1 mm/m = 63.4 in/mile, 1 mm = 0.04 in

National Highway Institute 4-36 REV-2, JAN 2006 IRI vs. Simulated PI for PCC Pavement 5-mm Blanking Band 2.5-mm Blanking Band Zero Blanking Band 1 mm/m = 63.4 in/mile, 1 mm = 0.04 in

National Highway Institute 4-37 REV-2, JAN 2006 Results of PI vs IRI Correlations l Correlations between IRI and PI were higher for zero blanking band when compared to 5 mm (0.2 in) blanking band l Results from TTI analysis: –IRI vs PI (5 mm [0.2 in] blanking band), R 2 = 0.58 –IRI vs PI (zero blanking band), R 2 = 0.85

National Highway Institute 4-38 REV-2, JAN 2006 Quiz l What is the difference between RN and IRI? l What is the Golden Car? l What is a blanking band? l What wavelengths affect IRI? l What wavelength affects RN?