Appendix E_FHWA_Distress_Identification_Manual.pdf

Appendix E

FHWA Distress Identification Manual for the Road Inventory Program

FHWA

DISTRESS

IDENTIFICATION

MANUAL

for the

Road

Inventory

Program

Developed by Federal Highway Administration

Updated for Cycle 7

TABLE OF CONTENTS

i. List of Figures

ii. List of Tables

iii. Preface

1 Surface Distresses

6 Alligator Cracking

10 Longitudinal Cracking

12 Transverse Cracking

14 Patching and Potholes

17 Rutting

20 Roughness

21 Macrotexture

22 Surface Types

24 Faulting

26 Index Formulas

26 Alligator Crack Index

26 Longitudinal Crack Index

27 Structural Crack Index

27 Transverse Crack Index

27 Patching Index

28 Rutting Index

28 Roughness Index

29 Surface Condition Rating (SCR)

29 Pavement Condition Rating (PCR)

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List of Figures

Figure 1 Figure 15 Measuring Crack Width on Asphalt

Pavement

Patching

Figure 2 Figure 16 Alligator Crack Severity Levels

Pothole Surrounded by Alligator Cracking

Figure 3 Figure 17 Alligator Crack Patterns of Differing

Severity

Full and Partial-Width Road Patching

Figure 4 Figure 18 High Severity Alligator Cracking

Measuring Rutting

Figure 5 Figure 19 Medium Severity Alligator Cracking

High Severity Rutting

Figure 6 Figure 20 Low Severity Alligator Cracking with

Few or No Interconnecting Cracks

Medium Severity Rutting

Figure 7 Figure 21 High Severity Longitudinal Cracking

Low Severity Rutting

Figure 8 Figure 22 Medium Severity Longitudinal Cracking

Macrotexture

Figure 9 Figure 23 Low Severity Longitudinal Cracking

Asphalt Surface Type

Figure 10 Figure 24

High Severity Transverse Cracking

Brick Surface Type

Figure 11 Figure 25

Medium Severity Transverse Cracking

Cobblestone Surface Type

Figure 12 Figure 26

Low Severity Transverse Cracking

Concrete Surface Type

Figure 13 Figure 27

Patching Variations

Faulting of transverse joint or crack

Figure 14 Figure 28

Patching Faulting of transverse joint

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List of Tables

Table 1 Table 3 Distress Summary

IRI & Roughness

Table 2 Alligator Crack Severity

Levels

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PREFACE

The Federal Highway Administration’s (FHWA) Road Inventory Program (RIP) for the National

Park Service (NPS), collects roadway condition data on paved asphalt surfaces including roads, parkways, and parking areas in National Park units nationwide. The road surface condition data is collected using an automated data collection vehicle.

The FHWA RIP is implemented based on the premise that an accurate pavement surface condition assessment can be accomplished using semi-automated crack detection technology as applied to digital images. Various methods of pavement condition assessment have been developed over the years with varying degrees of accuracy and acceptance. There has been continued improvement in crack detection and classification accomplished using high definition cameras, improved programming code and algorithms; both yielding continually more efficient crack detection and classification.

With the use of automated crack detection software and other distress detection systems, FHWA

RIP is tasked with executing a pavement condition assessment in Cycle 7 on about 11,000 miles of National Park Service roads and parkways. Foremost in setting up the basis of pavement distress identification is employing the distress identification protocols used by FHWA. There is no single distress identification system that is universal among entities conducting a program of distress identification. For the purpose of the NPS RIP, FHWA employs distress identification protocols that are specific to this program.

FHWA has referenced the “Distress Identification Manual for the Long-Term Pavement

Performance Program”, Publication No. FHWA-RD 03-031, June 2003, as the point-of-reference for distress types on NPS pavement. The FHWA RIP distress types are similar to those described in the LTPP manual with some modifications. Definitions of severity levels based on crack width contained in this document adhere to the LTPP Distress ID Manual.

Modifications have been made to the definition of Alligator and Longitudinal Cracking, and determination of Alligator Cracking severity. This manual also addresses rutting and roughness and its application to RIP.

In 2022, FHWA RIP will begin the seventh cycle of data collection in the National Park system.

For Cycle 7, data will be collected at least once in all parks with paved roads. For the purpose of collecting multiple data points in parks with higher mileage, some park units will get collected two times with the Data Collection Vehicle (DCV). The data is used to support the National

Park Service road maintenance program and Pavement Management System (PMS) developed and maintained by FHWA.

This “Distress Identification Manual for the NPS Road Inventory Program” will be used as a reference resource in crack detection and classification, rutting, faulting, roughness, macrotexture, determination of distress severity/extent, and in the calculation of distress index values for the Cycle 7.

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SURFACE DISTRESSES

Surface distresses are measured on asphalt surface types in the primary lane only. No cracking or rutting is reported on concrete. In the classification and measurement of all surface condition data, results will be reported in the database in intervals of 0.02 miles (105.6 feet) along the route.

Surface distresses determined from digital video images

• Transverse Cracks

• Longitudinal Cracks

• Alligator Cracks

• Patching/Potholes

Surface distress measured by the LRMS (Laser Rut Measurement System) on DCV (Data

Collection Vehicle)

• Rutting

Surface distress data are classified as listed above. The distresses are measured for severity and quantified for extent. Classification, severity, and extent of these five surface distresses comprise the components for calculation of SCR (Surface Condition Rating).

Additional condition data measured by DCV

• Roughness (IRI) - Roughness is measured and reported as International Roughness Index

(IRI) in inches/mile.

• Faulting distress (for concrete, rigid pavement surface types only)

• Macrotexture

Each of the five surface distresses is assigned a computed surface distress index

• Transverse Crack Index

• Longitudinal Crack Index

• Alligator Crack Index

• Patching/Pothole Index

• Rutting Index

IRI is assigned a computed Roughness Condition Index (RCI)

Using the SCR (computed from the five surface distresses) and the RCI, an overall Pavement

Condition Rating (PCR) is computed. The formula for PCR is:

Asphalt PCR = (0.60 * SCR) + (0.40 * RCI)

Concrete PCR = RCI

A detailed description is provided in this document for each distress index formula, roughness condition index, SCR and PCR.

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Each classified surface distress will fall into one or more severity…LOW, MEDIUM, or HIGH based on criteria listed. For each severity, an extent is established based on the measured quantity of the distress within that severity. Within each severity, individual distresses are assigned a Maximum Allowable Extent (MAE). For example, LOW severity transverse cracking may be allowed up to 21.1 cracks within a 0.02 interval before the index meets its MAE and fails. A PCR value of 60 is determined to be terminable serviceability and the road is considered failed. The MAE and index formulas are based on a scale of 0-100. A PCR index value of 100 would indicate a “perfect” road with no measurable distresses or rough ride. The range of PCR index values with condition descriptors are:

• POOR (<=60)

• FAIR (61 - 84)

• GOOD (85 - 94)

• EXCELLENT (95 - 100)

Index values are generally computed based on cumulative deducts of the measured severities.

As shown in the index formulas below, as any single severity reaches MAE, the index computes to a value of 60 and the road fails for that 0.02 interval.

*Note: Index values may occasionally compute to less than 0 or greater than 100. In this instance, an index value < 0 defaults to 0. Index values > 100 defaults to 100.

For all indices, a higher value indicates a better road condition, and a lower value indicates a poorer road condition.

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TABLE 1: Distress Summary

NOTES ON HPMA

In 2005, the FHWA began implementing the use of a Pavement Management System to assist the National Park Service in prioritizing Pavement Maintenance and Rehabilitation activities.

The PMS used by FHWA is the Highway Pavement Management Application (HPMA) and this software has the ability to manage and maintain the inventory and condition data from RIP. It predicts future performance using prediction models and as-built information. Outputs include performance and condition reports at the National, Region, Park, or Route levels. A regional prioritized list and optimization have been produced for all regions and the Federal Highway

Deferred Maintenance is calculated via the HPMA as well.

In an effort to improve the accuracy of treatment recommendations and pavement condition descriptions vis a vis the distresses and indexes that comprise the Pavement Condition Rating

ASPHALT-SURFACED PAVEMENT DISTRESS TYPES with RUTTING and ROUGHNESS

DISTRESS TYPE

UNIT OF

MEASURE… …CONVERTED TO

DEFINED

SEVERITY

LEVELS?

MEASURED

BY

Alligator

Cracking

Square Feet Percent of Lane Per 0.02

Mile

Yes Digital Image

Crack Detection

Software

Transverse

Cracking

Linear Feet Number of Cracks Per

0.02 Mile (1 crack =

width of distress lane)

Yes Digital Image

Crack Detection

Software

Longitudinal

Cracking

Linear feet Percent of Lane Length

Per 0.02 Mile

Yes Digital Image

Crack Detection

Software

Patching/Potholes Square Feet Percent of Lane Per 0.02

Mile

Yes Digital Image

Crack Detection

Software

Rutting Inches Rut Depth Per 0.02 Mile Yes Laser

Measurement

System

Roughness IRI RCI No Wheelpath lasers

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(PCR), an extensive study was completed throughout 2010 that resulted in changes to the Road

Inventory Program condition reporting method and specifically, the calculation of PCR. It was determined that a better representation of PCR could be achieved by modifying the relative impact certain distresses have on the overall rating.

Through the use of HPMA data, it was noted that false failure indicators existed with the existing

PCR model, and that it would be necessary to reduce their impact. The distresses affected in this way were Rutting and Roughness. Conversely, experience showed that roadways with extensive cracking present were often shown to have a high PCR. Therefore, the crack index models were adjusted to be more sensitive to changes in crack severity or quantity. It was also determined that these issues were not due to a problem with data acquisition (i.e. the RIP “van”), but with the way the collected data was processed. The final change was to provide guidance on when to use the Roughness Condition Index (RCI) in the PCR calculation. Roughness data is of little value to determining overall condition on routes that, due to their length or geometrics, have lower vehicle operating speeds. Therefore, starting in Cycle 5, only routes that have lengths of one half mile or greater and posted speed limits of 25 mph or greater will have RCI reported and included in the PCR calculations.

The PCR can be used to indicate the place in the Pavement Life Cycle and the types of treatments that should be considered now and into the future.

• Excellent/New: PCR of 95-100. Pavements in this range will require only spot repairs

• Good: PCR of 85-94. Pavements in this range will likely be candidates for Preventive

Maintenance. Examples include Chip and Slurry Seals, Micro Surfacing and Thin

Overlays.

• Fair: PCR of 61-84. Pavements in this range will likely be candidates of Light

Rehabilitation (L3R). Examples include single-lift overlays up to 2.5 inches in total thickness, milling and overlays.

• Poor: PCR of 60 or below. Pavements in this range will likely be candidates of Heavy

Rehabilitation or Reconstruction (H3R or 4R). Examples include Pulverization, Multiple

Lift Overlays, and Reconstruction.

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At this time, specific Maintenance and Rehabilitation activities should be evaluated and recommended at the project level. Site-specific conditions that influence treatment type should be determined based on performing a subsurface investigation and/or pavement condition survey, and not be based solely on RIP data. Additionally, RIP produces a snapshot of conditions the year in which the data was collected. For further information or to obtain additional Pavement

Management System’s data from our Highway Pavement Management Application (HPMA) please contact the Eastern Federal Lands pavement team.

P a v e m e n t C o n d it io n R a ti n g

Pavement Age

Condition Categories and Treatments

Reconstruction

POOR/Heavy Rehabilitation

GOOD/Preventive Maintenance

EXCELLENT/Localized Repairs Only

FAIR/Light Rehabilitation

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ALLIGATOR CRACKING

Description

Alligator cracking is considered a combination of fatigue and block cracking. It is a series of interconnected cracks of various stages of development. Alligator cracking develops into a many-sided pattern that resembles chicken wire or alligator skin. It can occur anywhere in the road lane. Alligator cracking must have a quantifiable area.

Severity Levels

LOW

An area of cracks with no or very few interconnecting cracks and the cracks are not spalled. Cracks are <= 0.25 in (6 mm) in mean width. Cracks in the pattern are no further apart than 1 foot (0.328 m). May be sealed cracks with sealant in good condition and a crack width that cannot be determined.

MEDIUM

An area of interconnected cracks that form a complete pattern. Cracks may be slightly spalled. Cracks are >0.25 in. (6 mm) and <= 0.75 in. (19 mm) or any crack with a mean width <= 19 mm and adjacent low severity cracking. Cracks in the pattern are no further apart than 6 in. (150 mm).

HIGH

An area of interconnected cracks forming a complete pattern. Cracks may have large areas of spalling, missing material and/or potholes. Cracks are >0.75 in (19mm) or any crack with a mean width <= 0.75 in (19mm) and adjacent medium to high severity random cracking.

A combination of observed crack width and crack pattern is used to determine overall severity of alligator cracking. Based on above description of each severity, the highest level of crack width and crack pattern determines overall severity. Table 2 illustrates this.

TABLE 2: Alligator Crack Severity Levels

ALLIGATOR CRACKING

SEVERITY LEVELS

Crack Pattern

LOW MED HIGH

C ra ck

W id th

LOW L M H

MED M M H

HI H H H

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FIGURE 1: Measuring Crack Width on Asphalt Pavement

FIGURE 2: Effect on Severity Level of Alligator Cracking due to Associated Random

Cracking

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FIGURE 3: Alligator Crack Patterns of Differing Severity

FIGURE 4: High Severity Alligator Cracking

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FIGURE 5: Medium Severity Alligator Cracking

FIGURE 6: Low Severity Alligator Cracking with Few or No Interconnecting Cracks

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LONGITUDINAL CRACKING

Longitudinal cracking occurs predominantly parallel to the pavement centerline. It can occur anywhere within the lane. Longitudinal cracks occurring in the wheelpath may be noteworthy.

Cracks with a mean width of <= 0.25 in. (6 mm). This also includes sealed cracks with sealant in good condition and a width that cannot be determined.

MED

Cracks with a mean width > 0.25 in. (6 mm) and <= 0.75 in. (19 mm). Also, any crack with a mean width < 0.75 in. (19 mm) and adjacent random low severity cracking.

Cracks with a mean width > 0.75 in. (19 mm). Also, any crack with a mean width < 0.75

in. (19 mm) and adjacent random medium to high severity cracking. Cracks may have large areas of spalling, missing material and/or potholes

FIGURE 7: High Severity Longitudinal Cracking

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FIGURE 8: Medium Severity Longitudinal Cracking

FIGURE 9: Low Severity Longitudinal Cracking

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TRANSVERSE CRACKING

Transverse cracking occurs predominantly perpendicular to the pavement centerline. It can occur anywhere within the lane.

Cracks with a mean width of < 0.25 in. (6 mm). Sealed cracks with sealant in good condition and a width that cannot be determined.

Cracks with a mean width > 0.25 in. (6 mm) and <= 0.75 in. (19 mm). Also, any crack with a mean width < 0.75 in. (19 mm) and adjacent random low severity cracking.

Cracks with a mean width > 0.75 in. (19 mm). Also, any crack with a mean width < 0.75

in. (19 mm) and adjacent random medium to high severity cracking.

FIGURE 10: High Severity Transverse Cracking

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FIGURE 11: Medium Severity Transverse Cracking

FIGURE 12: Low Severity Transverse Cracking

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PATCHING AND POTHOLES

Patching is an area of pavement surface that has been removed and replaced with patching material or an area of pavement surface that has had additional patching material applied.

Patching may encompass partial lane or full lane width With full lane width patching, the total contiguous length of patch may not exceed 0.100 mi. (0.161 km). Any full-lane patch exceeding

0.100 mi. in length is considered a pavement change. Patching must have a quantifiable area.

- Hot mix asphalt (HMA) patching should be distinguished from cold patching during collection. Given the short-term nature of cold patches, these will be assigned a higher severity level.

- Potholes are bowl-shaped holes of various sizes occurring in the pavement surface.

Potholes can be grouped with cold patches for identification purposes.

- Manhole covers should not be rated as patches unless there is obvious patching around the manhole.

- Speed bumps should not be rated as patches

HMA/sawcut patching areas

Pothole areas (including cold patches). Potholes and cold patching that are in conjunction with other cracking (i.e. Alligator/Longitudinal) should be classified as High

Severity for that type of cracking and not included in this index (see High Severity section of those respective distresses). Only potholes and cold patches with no other cracking distress present should be classified in the High Severity level of this Patching and Potholes index.

FIGURE 13: Patching Variations

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FIGURE 14: Patching

FIGURE 15: Patching

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FIGURE 16: Pothole Surrounded by Alligator Cracking classify as Alligator Cracking

FIGURE 17: Full and Partial-Width Road Patching

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RUTTING

Rutting is a longitudinal surface depression in the wheelpath.

Ruts with a measured depth ≥ 0.20” and ≤ 0.49”

Ruts with a measured depth ≥ 0.50” and ≤ 0.99”

Ruts with a measured depth ≥ 1.00”

Ruts < 0.20” are not included in the distress calculations.

FIGURE 18: Measuring Rutting

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FIGURE 19: High Severity Rutting

FIGURE 20: Medium Severity Rutting

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FIGURE 21: Low Severity Rutting

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ROUGHNESS

Roughness is the measurement of the unevenness of the pavement in the direction of travel. It is measured in units of IRI (International Roughness Index), inches per mile, and is indicative of ride comfort.

There are no stratified severity levels for roughness. The roughness (or smoothness) of a road surface can be defined by IRI in the following table.

TABLE 3: IRI & Roughness

IRI Descriptions

Type of Road Typical IRI (in/mile )

New Pavement 32 – 63

New Road, no noticeable roughness 63 – 94

Small level of roughness 94 – 126

Road of average roughness 126 – 190

Road with above average roughness 190 – 253

Road with severe roughness 253 – 380

Nearly impassable 380 -

Roughness Collection Parameters

On shorter roads with a lower speed limit the usefulness in collecting and reporting IRI is negligible. Lower, inconsistent speeds can lead to a less accurate IRI value. Therefore, RIP has put in place the following protocols for reporting IRI.

IRI will not be reported on routes meeting either of the following factors:

• Posted speed limit is less than 25 mph

• Length of route is less than 0.500 miles

Other unique situations may arise where neither of these factors are met, but IRI reporting may not be appropriate. For example, a windy road where the collection vehicle cannot maintain a consistent speed.

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Macrotexture

Macrotexture is a category of pavement texture that includes wavelengths from 0.5 mm to 50

mm. The texture of a pavement is important to measure as it can indicate the road’s resistance to skidding. The macrotexture of a pavement is the measurement of the voids between the aggregate on the pavement surface. The result of the measurement may aid in determining the skid resistance capability of the pavement.

There are no stratified severity levels for macrotexture. The macrotexture of a road surface can be defined by the Mean Profile Depth (MPD). Measured over a specific segment of road (e.g.

1cm), the mean depth is the difference in depth from minimum or maximum measurements made along a segment of roadway.

FIGURE 22: Macrotexture

Macrotexture Collection Parameters

The Mean Profile Depth (MPD) should only be calculated for the right wheelpath on asphalt pavements. Mean Profile Depth is calculated by following ASTM E1845-15 “Standard Practice for Calculating Pavement Macrotexture Mean Profile Depth.”

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SURFACE TYPES

FIGURE 23: Asphalt Surface Type

FIGURE 24: Brick Surface Type

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FIGURE 25: Cobblestone Surface Type

FIGURE 26: Concrete Surface Type

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FAULTING

Faulting is a vertical misalignment of pavement joints in Jointed Portland Cement Concrete

Pavements (JPCP). JPCP is defined as pavements where the top-most surface is constructed of

Portland cement concrete with joints. The average absolute Faulting of all transverse joints in a section is reported to the nearest 0.01 inch. Reporting shall be consistent with IRI inventory direction lane, and section. Zero (0) values shall only be reported for roadway sections where faults are not present.

Data collection method for faulting data shall be in accordance with AASHTO Standard R 36, “Standard Specification for Transportation Materials and Methods of Sampling and Testing, Standard Practice for Evaluating Faulting of Concrete Pavements.” Measure the fault according to either Method A or Method B as described in the most recent version of AASHTO R36 for automated measurements based profile data collected for the right wheelpath and is to be reported as the average absolute faulting of the right wheelpath for the measured section and that faulting at cracks should not be included, only faulting at joints should be included. Every joint should be measured in the right wheelpath over the section and the average absolute faulting reported.

Fault < 0.1”

Fault ≥ 0.1”, and ≤ 0.15”

Fault > 0.15”

FIGURE 27: Faulting of transverse joint or crack

A

A

B

B

Traffic

Fault (positive) Fault (negative)

Traffic

Joint

Edge Joint

Joint

Shoulder

CL

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FIGURE 28: Faulting of transverse joint

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INDEX FORMULAS

Notes:

All index formulas listed below contain MAE applicable to 0.02 mile (105.6 feet) interval.

In 2022, FHWA is investigating updates to the equations for Patching Index and Roughness

Condition Index (RCI). These updates are not reflected in this manual as of March 2022.

Alligator Crack Index

AC_INDEX = 100 – 40 * [(%LOW / 35) + (%MED / 15) + (%HI / 5)]

Where:

The values %LOW, %MED and %HI report the percentage of the observed pavement

(0.02 mile, primary lane) that contains alligator cracking within the respective severities.

These values range from ≥ 0 to ≤ 100.

%LOW = Percent of total area (primary lane, 0.02 in length), low severity

%MED = Percent of total area (primary lane, 0.02 in length), medium severity

%HI = Percent of total area (primary lane, 0.02 in length), high severity

Percent of total area is computed as:

square foot area of alligator crack severity

0.02 mile * lane width

In AC_INDEX, the denominators 35, 15, and 5 are the Maximum Allowable Extents

(MAE) for each severity. In other words, we will allow up to 35% of low severity alligator cracking for a 0.02 interval before failure, or 15% for medium severity, or 5% high severity. As you can see, if any single severity reaches MAE the resulting index value is 60, or failure.

Longitudinal Crack Index

LC_INDEX = 100 – 40 * [(%LOW / 175) + (%MED / 75) + (%HI / 25)]

The values %LOW, %MED, and %HI report the length of longitudinal cracking within each severity as a percent of the section length (0.02 mile, primary lane).

These values are ≥ 0 and can exceed 100.

%LOW = Percent of interval length (primary lane, 0.02 in length), low severity

%MED = Percent of interval length (primary lane, 0.02 in length), medium severity

%HI = Percent of interval length (primary lane, 0.02 in length), high severity

Percent of interval length is computed as:

length of respective longitudinal cracking

0.02 mile (105.6 feet)

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In LC_INDEX, the denominators 175, 75, and 25 are the Maximum Allowable Extents

(MAE) for each severity. In other words, we will allow up to 175% of low severity alligator cracking for a 0.02 interval before failure, 75% for medium severity, and so on.

As you can see, if any single severity reaches MAE the resulting index value is 60, or failure.

Structural Crack Index

SC_INDEX = [100 - ((100 - AC_INDEX) + (100 - LC_INDEX))]

Structural Crack Index is a combination of Alligator Cracking and Longitudinal Cracking, and is used in the SCR formula in lieu of AC and LC separately.

Transverse Crack Index

TC_INDEX = 100 – 40 * [(LOW / 21.1) + (MED / 4.4)) + (HI / 2.6)]

The values LOW, MED and HI report a count of the total number of transverse cracks

(reported to three decimals) within each severity level, where one transverse crack is equal to the lane width. These values are ≥ 0.

LOW = Number of cracks in interval (primary lane, 0.02 in length), low severity

MED = Number of cracks in interval (primary lane, 0.02 in length), medium severity

HI = Number of cracks in interval (primary lane, 0.02 in length), high severity

Number of cracks per 0.02 mile section is computed as:

Total length of transverse cracks

Distress lane width

In TC_INDEX, the denominators 21.1, 4.4, and 2.6 are the Maximum Allowable Extents

(MAE) for each severity. In other words, we will allow up to 21.1 full lane width low severity transverse cracks for a 0.02 interval before failure, 4.4 cracks for medium severity, and so on. As you can see, if any single severity reaches MAE the resulting index value is 60, or failure.

Patching Index

PATCH_INDEX = 100 – 40 * (%PATCHING / 80)

The value %PATCHING reports the percentage of the observed pavement (0.02 mile, primary lane) that contains patching/potholes. This value ranges from ≥ 0 to ≤ 100.

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%PATCHING = %LOW + %HI (Percent of total area (primary lane, 0.02 in length))

Percent of total area is computed as:

square foot area of patching/potholes

0.02 mile * lane width

There are no severity levels for patching. It either exists or does not.

In PATCH_INDEX, the denominator 80 is the Maximum Allowable Extent (MAE) for each severity. In other words, we will allow up to 80% patching for a 0.02 interval before failure. As you can see, if patching/potholes reaches MAE the resulting index value is 60, or failure.

Rutting Index

RUT_INDEX = 100 – 40 * [(%LOW / 535) + (%MED / 205) + (%HI / 40)]

20 rut depth measurements are taken per 0.02 interval for each of 2 wheel paths (left and right), resulting in a total of 40 measurements taken for both wheel paths. The values

%LOW, %MED and %HI report the percentage of the 40 measurements within that severity. These values range from ≥ 0 to ≤ 200.

%LOW = Percent of LOW ruts in left wheelpath based on 20 ruts, plus percent of LOW ruts in right wheelpath based on 20 ruts.

%MED = Percent of MED ruts in left wheelpath based on 20 ruts, plus percent of MED ruts in right wheelpath based on 20 ruts.

%HI = Percent of HI ruts in left wheelpath based on 20 ruts, plus percent of HI ruts in right wheelpath based on 20 ruts.

Percent of rut measurements within each severity is computed as:

Number of ruts within each severity

20 * 100

In RUT_INDEX, the denominators 535, 205, and 40 are the Maximum Allowable

Extents for each severity; Low, Medium, and High, respectively. Only the MAE for high severity rutting can fail a section, since 200% of only low severity ruts would yield a rut index of 85 and 200% of only medium severity ruts would yield a rut index of 61.

Roughness Condition Index (Asphalt)

RCI = 32 * [5 * (2.718282 ^ (-0.0041 * AVG IRI))]

The value AVG IRI reports the average value of the Left IRI and Right IRI measurements for the interval (0.02 mile, primary lane). This value can range from approximately 40 to over 1000.

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Average IRI is computed as:

Left wheelpath IRI + Right wheelpath IRI

There is no applicable threshold for failure for this index.

Roughness Condition Index (Concrete)

RCI = -0.0012(IRI2) + 0.0499(IRI) + 99.542

For concrete, PCR = RCI

Surface Condition Rating Index

SCR = Lowest Index Value Of: [SC_INDEX, TC_INDEX, PATCH_INDEX, RUT_INDEX]

Note: The modified SCR equation above combines AC_INDEX and LC_INDEX, and considers that value a single AC/LC index value, which is called the SC_INDEX or Structural

Crack Index. The lowest of the four computed index values becomes the SCR.

See above for determinations of AC_INDEX, LC_INDEX, SC_INDEXT, TC_INDEX, PATCH_INDEX and RUT_INDEX.

The threshold for failure for this index is SCR = 60.

Pavement Condition Rating Index (Asphalt)

PCR = (0.60 * SCR) + (0.40 * RCI)

See above for determinations of SCR and RCI.

The values 0.60 and 0.40 function as weights within the formula.

Note: If SCR equals zero, then the formula simply reduces to: PCR = 0.40 * RCI.

If RCI equals “-1” (which means that RCI was unattainable), then the formula becomes:

PCR = SCR.

The threshold for failure for this index is PCR = 60.

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Pavement Condition Rating Index (Concrete)

PCR = RCI for concrete

Note: If RCI is unattainable for a concrete route, a manual assessed PCR may be given.