APPENDIX E

Measuring Pavement Roughness

## Introduction {#introduction .HPMS-Heading-3}

In order to provide a measure of pavement surface condition that has
nationwide consistency and comparability and is as realistic and
practical as possible, a uniform, calibrated roughness measurement for
paved roadways is required by the HPMS.

Roughness is defined in accordance with ASTM E867 as "The deviation of a
surface from a true planar surface with characteristic dimensions that
affect vehicle dynamics and ride quality." After a detailed study of
various methodologies and road profiling statistics, the International
Roughness Index (IRI) was chosen as the HPMS standard reference
roughness index. The summary numeric (HPMS data reporting unit) is the
IRI in meters/kilometer (inches/mile). The primary advantages of the IRI
are:

1.  It is a time-stable, reproducible mathematical processing of the
    known profile.

2.  It is broadly representative of the effects of roughness on vehicle
    response and user's perception over the range of wavelengths of
    interest, and is thus relevant to the definition of roughness.

3.  It is a zero-origin scale consistent with the roughness definition.

4.  It is compatible with profile measuring equipment available in the
    U.S. market.

5.  It is independent of section length and amenable to simple
    averaging.

    6.  It is consistent with established international standards and
        able to be related to other roughness measures.

## HPMS Roughness Measurement Procedure {#hpms-roughness-measurement-procedure .HPMS-Heading-3}

The reference method for obtaining IRI data for the HPMS can be found in
the AASHTO Standard Practice for Determination of International
Roughness Index for Quantifying Roughness of Pavements, AASHTO PP 37-04.
This Standard Practice calls for the use of a longitudinal profile
measured in accordance with ASTM E-950 as a basis for estimating IRI.
AASHTO PP 37-04 is reproduced in this appendix with the written consent
of AASHTO. Roughness is reported for HPMS in IRI units of either m/km or
in/mi (1 m/km = 63.36 in/mi).

Roughness data should be reported in IRI units for all sections in
accordance with Table IV-1 in Chapter IV. The lower functional systems
(rural and urban collector and urban minor arterial) have been placed in
the "recommended" category since there are situations where it may not
be possible to obtain meaningful roughness measurements with profiling
equipment. Major obstacles include:

> Speed restrictions Traffic congestion
>
> Short section lengths Pavement treatments
>
> Numerous traffic signals Intersection treatments

However, some of these obstacles can be overcome by collecting roughness
data during non-peak hours or at night, where speed, traffic, and safety
are less of a problem. There are situations where it also may not be
possible to obtain meaningful roughness measurements on some urban other
principal arterial sections. In these cases, a value of "0" may be
reported.

All equipment must be operated within manufacturer's specifications;
quality assurance guidelines outlined in AASHTO PP 37-04, Section 5, and
Appendix B, must be followed. Each State should document and retain
records of its quality assurance procedures; FHWA field offices should
monitor adherence to these procedures as part of roughness data process
reviews.

## Additional Recommendations for Collection of Roughness Data {#additional-recommendations-for-collection-of-roughness-data .HPMS-Heading-3}

The following field survey guidelines are recommended for State use in
addition to the AASHTO Standard Practice:

-   Where roughness data are collected in both directions, the State
    should use the "inventory direction" selected in accordance with the
    discussion on page IV-2 of the HPMS Field Manual for reporting IRI
    data and should use this same direction for all future HPMS
    reporting.

-   For multi-lane facilities, roughness data for the outside (right)
    lane should be reported. However, if this is not practical,
    whichever lane is measured should be used for all future HPMS
    reporting.

-   Roughness data collection should be performed when the pavement is
    in stable condition. Data should not be collected during winter
    (frost/freeze or freeze/thaw) or wet base conditions. Data
    collection should be performed during good weather conditions when
    wind conditions will not affect equipment stability and on dry
    pavement. All equipment manufacturer's recommended procedures should
    be observed.

-   Data should only be collected at the speeds that correspond to the
    manufacturer's recommended speed range. Constant speeds should be
    maintained for all measurements within specified ranges.

-   Exclude the impacts of bridge approaches and railroad crossings (or
    other localized discontinuities) from the roughness measurement for
    the roadway. Bridge decks should not be included; the objective is
    to obtain a measure of pavement not bridge roughness.

-   Roughness measurements should be taken over the entire length of an
    HPMS roadway section. However, in order to achieve equipment and
    speed stability, a minimum run-in length, consistent with the
    manufacturer's specification, may be required prior to the beginning
    of the measurement area. If this minimum cannot be met prior to the
    start of the sample section, a shorter portion of the HPMS section
    may be measured, but that same portion should always be measured in
    future roughness data collection activities. Short HPMS sections
    also may be included in slightly longer roughness test sections for
    measurement and reporting purposes. However, the same longer
    sections should always be measured in future data collections.

## Coordination with Other Activities {#coordination-with-other-activities .HPMS-Heading-3}

One of the goals of HPMS is to avoid duplicate data collection efforts.
States are encouraged to coordinate roughness measurement activities,
where possible, such that the same equipment, verification sites, and
measurements are used for multiple purposes. Therefore, HPMS activities
should be coordinated with other State activities such as the Strategic
Highway Research Program (SHRP)/Long Term Pavement Performance (LTPP)
and the State Pavement Management Systems (PMS).

The LTPP activities monitor pavement performance and use in detail for
approximately 1,500 pavement sections nationwide as part of SHRP. The
pavement and traffic monitoring data collected on LTPP sections should
be used for the HPMS universe or standard sample sections where
possible. In addition, efforts should be made to utilize the LTPP
established sections/profiles as multiple-use verification sections in
each State.

Many State and some local transportation agencies have operational or
are developing a PMS to guide program development, improve life-cycle
costs, and help select the most effective pavement improvement
strategies. The HPMS pavement data reporting should make full use of
existing PMS data and collection activities. Data collected by others
(cities, counties, MPO's, etc.) should be subjected to the same AASHTO
quality assurance guidelines before incorporation into the HPMS.

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