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Ride Quality Specifications - Smoothing Out
Pavements

• Richard Wix

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Outcomes of Presentation

• What is ride quality and how does it relate to
  road roughness?
• How is ride quality measured?
• How can a basic understanding of IRI lead to a
  road with a smoother ride?

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Why is Ride Quality of Importance?

• Reduces dynamic loading
• Increases life expectancy
• Decreases road user costs
• Increases user satisfaction
• SRAs implementing Ride Quality testing for rehab
  and new construction

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What is Ride Quality?

• the level of ride comfort experienced by the
  occupants of a vehicle as it traverses the
  pavement
• dependent on vertical acceleration experienced by
  occupants
• acceleration attributable to roughness

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What is Roughness?

• a condition parameter which characterises
  deviations from the intended longitudinal profile
  of a road surface with characteristic dimensions
  that affect vehicle dynamics... ride quality and
  dynamic pavement loading (Austroads 2001)
• a lack of smoothness

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Roughness Measurement in Australia

• In 1970s ARRB in conjunction with SRAs developed
  the NAASRA roughness meter
• Response Type Road Roughness Measurement System
  (RTRRMS)
• Must be calibrated

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Inertial Laser Profiler

• Introduced in Australia in the late 1980s to
  calibrate NAASRA meter
• Measurements are independent of vehicle dynamics
• Combines the outputs from a laser and
  accelerometer to give profile

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IRI - What is it?

• Outcome of the World Bank initiated IRRE in
  Brazil in 1982
• Quarter car model (mathematical filter)
• High correlation to vertical passenger
  acceleration at 80 km/h

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Roughness is ?
Defects
.and everything in between
Dips
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IRI Gain Response
2.4 m
15.4 m
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Things to Keep in Mind When Smoothing out
Pavements

• Steps and construction joints
• Dips, humps and bumps
• Keeping it (the road surface) clean
• Site location and delineation
• Providing sufficient lead-in and lead-out

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Steps

• a change in height that occurs at a discrete
  point in the pavement (Austroads 2002)
• short duration defect
• often occur at a bridge abutment or termination
  of overlay

h
h step height
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Effect of Step Height on IRI
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Construction Joints
Usually manifested as a small dip or bump across
pavement
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Avoiding Steps and Construction Joints

• Utilise a continuous paving technique to avoid
  any discontinuity
• When placing asphalt be wary of the supply truck
  bumping the paver

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Dips, Humps Bumps

• Long wavelength defect
• Built into underlying layers
• Minimal improvement in ride quality if thin
  surfacing applied
• Shape correction must be used to cater for longer
  wavelength

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Dips, Humps and Bumps

• 20 metre wave length
• 10 mm amplitude
• No surface defects
• IRI 2.34 m/km

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Keeping the Road Surface Clean

• Surface contaminants can have a significant
  effect on ride
• Measuring device unable to differentiate dirt
  from pavement
• Sweep surface remove loose gravel, dirt and
  clay
• One of the easier things to do

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Site Location Delineation

• Clearly identify start and end points using
  physical markers
• Meet the testing authority on site
• Utilise guides eg bollards to assist in tracking
  if unsealed or no line marking

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Lead-in

• Must be of sufficient length to reach operating
  speed commence acquisition
• Sufficiently long to avoid sharp acceleration
• Minimum 20 metres, ideal 50 metres
• Free of any defects (flow on effect)

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Flow on Effect
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If the surface is too rough.

• Correction will be required otherwise penalties
  may apply
• Identify offending section of pavement by
  analysing data at a smaller interval
• (Avoid need for rework by testing prior to
  application of final surfacing)

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Suitability of Measuring Equipment

• If IRI is required use a laser profiler or
  Walking Profiler
• Use an accredited supplier (this is stipulated by
  several SRAs)

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Conclusions

• Roughness (IRI) is a good measure of ride quality
• Roughness is more than just potholes and
  corrugations
• Penalties can be avoided if contractors are aware
  of factors affecting ride quality
• (Provision of incentives)

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Thank you

• Questions???