Development of Surface Roughness Standards for Pathways Used by Wheelchair Users: Final Report

APPENDIX D

PROPOSED ASTM INTERNATIONAL STANDARD

Computing Pathway Roughness Index from Longitudinal Profile Measurements¹

¹This standard practice is under the jurisdiction of ASTM Committee E17 on Vehicle-Pavement Systems and is the direct responsibility of Subcommittee E17.33 Methodology for Analyzing Pavement Roughness

1. Scope

1.1 This practice covers the mathematical processing of longitudinal profile measurements to produce a pedestrian pathway roughness statistic called the Pathway Roughness Index (PRI).

1.2 This provides a standard practice for computing and reporting an estimate of pathway roughness for sidewalks and other pedestrian surfaces.

1.3 This practice is based on an algorithm developed at the University of Pittsburgh Human Engineering Research Laboratories sponsored by United States Access Board grants H133E070024 and H133N110011 and reported in a Transportation Research Board (TRB) paper [5].

1.4 The values stated in SI units are to be regarded as the standard. The inch-pound units given in parentheses are for information only.

1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

2. Referenced Documents

2.1 ASTM standards

E867 Standard Terminology Relating to Vehicle-Pavement Systems

E1364 Standard Test Method for Measuring Road Roughness by Static Level Method

E1926 Standard Practice for Computing International Roughness Index of Roads from Longitudinal Profile Measurements¹

E1927 Standard Guide for Conducting Subjective Pavement Ride Quality Ratings

E2133 Standard Test Method for Using a Rolling Inclinometer to Measure Longitudinal and Transverse Profiles of a Traveled Surface

¹This standard practice is under the jurisdiction of ASTM Committee E17 on Vehicle-Pavement Systems and is the direct responsibility of Subcommittee E17.33 Methodology for Analyzing Pavement Roughness

3. Terminology

3.1 Definitions:

3.1.1 Terminology used in this practice conforms to the definitions included in Terminology E867.

3.1.1.1 longitudinal profile measurement, n—a series of elevation values taken at a constant interval along a wheel track.

3.1.1.1.1 Discussion—Elevation measurements may be taken statically, as with rod and level per Test Method E1364 or dynamically using a rolling inclinometer per Test Method E2133.

3.1.1.2 traveled surface roughness—the deviations of a surface from a true planar surface with characteristics dimensions that affect vehicle dynamics, ride quality, dynamic loads, and drainage, for example, longitudinal profile, transverse profile, and cross slope.

3.1.1.3 wave number, n—the inverse of wavelength.

3.1.1.3.1 Discussion—Wave number, sometimes called spatial frequency, typically has units of cycle/m or cycle/ft.

3.1.2 Definitions of Terms Specific to This Standard:

3.1.2.1 Pathway Roughness Index (PRI), n—an index computed from a longitudinal profile measurement using a standard 70 mm (2.5 in.) diameter wheel with no deformation and no affects from speed. The index will be a representation of the total vertical deflection of that wheel as it would travel over the surface.

3.1.2.1.1 Discussion—PRI is reported in either millimeters per meter (mm/m) or inches per foot (in./ft).

3.1.2.2 Mean Pathway Roughness Index (MPRI), n—the average of the PRI values for multiple trials

3.1.2.2.1 Discussion—Units are in millimeters per meter or inches per foot.

3.1.2.3 true Pathway Roughness Index, n—the value of PRI that would be computed for a longitudinal profile measurement with the constant interval approaching zero.

3.1.2.4 wheel path, n—a line or path followed by a non-deformable tire of a wheeled vehicle on a traveled surface as it approaches zero speed.

4. Summary of Practice

4.1 This practice was developed specifically for estimating pathway roughness from longitudinal profile measurements.

4.2 Longitudinal profile measurements for one wheel track are transformed mathematically by a computer program and accumulated to obtain the PRI. The profile must be represented as a series of elevation values taken along with a series of horizontal distance values along the wheel track.

4.3 The PRI scale starts at zero for a surface with no roughness and covers positive numbers that increase in proportion to roughness. Figure 1 provides PRI value descriptors from research conducted at the Human Engineering Research Laboratories for simulated and community surfaces made of wood, segmental paving units, cast-in-place concrete, and asphalt.

5. Significance and Use

5.1 This practice provides a means for obtaining a quantitative estimate of a surface property defined as roughness using longitudinal profile measuring equipment.

5.1.1 The PRI is portable in that it can be obtained from longitudinal profiles obtained with a variety of instruments.

5.1.2 The PRI is stable with time because true PRI is based on the concept of a true longitudinal profile, rather than the physical properties of a particular type of instrument.

5.2 Roughness information will be a useful input to the pathway and sidewalk management systems maintained by municipal agencies.

5.2.2 When profiles are measured simultaneously for multiple traveled wheel tracks, then the MRI is considered to be a better measure of pathway surface roughness than the PRI for either wheel individually.

5.3 Pathway roughness data will be useful when determining the vibration exposure that a wheelchair user will experience.

5.3.1 Vibration exposure has been linked to pain and injuries in wheelchair users and the PRI of traveled surfaces will provide the ability to quantify the vibration exposure a wheelchair user will experience when traveling that surface.

5.3.2 Knowledge of the vibration exposure a wheelchair user will experience on traveled surfaces will allow them to take steps to minimize their exposure, reducing the likelihood of pain and injury.

NOTE 1—The MRI scale is identical to the PRI scale.

Fig. 1: Pathway Roughness Index and Ratings

6. Longitudinal Profile Measurement

6.1 The longitudinal profile measurements can be obtained from equipment that operate in a range of speeds from static to meters per second.

6.2 The elevation profile measuring equipment used to collect the longitudinal profile data used in this practice must have sufficient accuracy to measure the longitudinal profile attributes that are essential to the computation of the PRI.

7. Computation of Pathway Roughness Index

7.1 This practice computes a PRI from an algorithm developed at the Human Engineering Research Laboratories and described in the TRB paper [5].

7.2 The distance interval over which the PRI is computed is discretionary, but shall be reported along with the PRI results.

8. Report

8.1 Include the following information in the report for this practice:

8.1.1 Profile Measuring Device—The Class of the profile measuring device used to make the profile measurement per Test Method E2133 and Test Method E1364.

8.1.2 Longitudinal Profile Measurements—Data from the profile measuring process shall include the date and time of day of the measurement, the location of the measurement, length of measurement, and the descriptions of the surface being measured.

8.1.3 PRI Resolution—If units reported are mm/m, then report the PRI within two decimals. If the reported units are in./ft., then report the PRI within three decimals.

8.1.4 Profile Segment—If the entire profile of a measured surface was not used in the calculation of the PRI value, the report shall include which segment of the profile was used.

9. Precision and Bias

9.1 The precision and bias of the computed PRI is limited by the procedures used in making the longitudinal profile measurement.

9.2 For the effects of the precision and bias of the measured profile on the computed PRI, see precision and bias in Appendix X1.

10. Keywords

10.1 roughness; sidewalk; pathway roughness index; pathway; longitudinal profile; pedestrian.