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Section 9: Ride Quality

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Ride Quality Parameter (IRI)

IRI is the International Roughness Index and measures pavement smoothness. The lower the calculated IRI, the smoother the pavement will ride. The higher the IRI, the rougher the pavement will ride. The units of IRI are usually in./mile, m/km, or mm/m. For more detailed information on IRI, refer to The Little Book of Profiling (Sept 1998) by Michael W. Sayers and Steven M. Karamihas.

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Equipment for Measuring Ride Quality

The inertial profiler is a device that uses laser sensors to measure the profile of the pavement surface. There are generally three types of inertial profilers:

  1. one that can travel at highway speeds, a high speed profiler,
  2. a light weight profiler that can travel at a minimum speed of 12 mph, and
  3. a portable profiler.

Figure 6-54 and Figure 6-55 are pictures of a high speed profiler and a light weight profiler.

High Speed Inertial Profiler.
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Figure 6-54. High Speed Inertial Profiler. © Copyright 2006 University of Washington

Light Weight Profiler.
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Figure 6-55. Light Weight Profiler. © Copyright 2006 University of Washington

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Pay Schedule

The pay schedule is used to determine the level of bonus or penalty for each 0.1-mi. section on the project. Pay schedules 1 and 2 have the same bonus schedule. Under Item 585, pay schedule 3 has a lower bonus schedule than pay schedules 1 and 2. Penalty schedule is most severe for schedule 1 less severe for schedule 2 and there is no penalty for schedule 3. The Construction Division has a written guideline that should be used to determine the most appropriate pay schedule. The pay schedule should be selected based on the existing IRI, class of the road, posted speed, the number of smoothness opportunities, and other mitigating factors. Refer to the Guidance Document on Item 585 Ride Quality for Pavement Surfaces for more detail.

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Smoothness Opportunity

A smoothness opportunity is defined as a chance for the contractor to improve ride quality. Examples:

  1. placing an overlay on an existing pavement surface is considered one smoothness opportunity,
  2. placing a level up and overlay is considered two smoothness opportunities,
  3. hot in-place recycling with a new overlay is considered two smoothness opportunities, and
  4. grading for a base course is considered one smoothness opportunity.

Spot level-ups, milling operations, or seal coats are not considered a smoothness opportunity. Mill and fill operations that require matching the existing pavement are not considered a smoothness opportunity.

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Analysis of Ride Data

The ride data is analyzed using TxDOT’s Ride Quality computer program. The analysis includes a description of the project:

District, county, highway, beginning reference marker, end reference marker, CSJ, lane designation, IRI values every 0.1 mile, pay, locations of bumps or dips and total pay adjustment.


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