Pavement Preservation and the Role of Bituminous Surface TreatmentsA Washington State View

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Pavement Preservation and the Role of Bituminous
Surface TreatmentsA Washington State View
Rocky Mountain Asphalt Conference
February 20, 2009
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The Situation

• WSDOT policy, in essence, mandated use of BSTs
  for routes with an ADT lt 2,000.
• Pavement preservation funding level (real
  dollars) is down.
• Pavement preservation funding is a WSDOT account
  used to pay for contract HMA and BST projects.
• Questions
• What is a reasonable ADT upper limit for
  application of BSTs?
• What kinds of pavement performance can we expect
  if more BSTs are done and fewer HMA overlays?

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WSDOT Pavements by Surface Type
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Preservation Policies and Practices
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WSDOT Lane-Miles by ADT
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FHWA IRI Thresholds for Interstate Highways
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Existing IRI Sorted by ADT
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WSDOTPavement Preservation Funds
Note 1 Includes project engineering,
construction engineering, safety, taxes. Note 2
Funds shown unadjusted for inflation.
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Percentages of Pavement Preservation Funding by
Type
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Preservation Pinch
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Preservation Funds by Lane-Mile per Year
Note 1 Funding shown includes project
engineering, construction engineering, safety,
and taxes. Note 2 Amounts shown not adjusted for
inflation.
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Initial Bottom Line

• Not enough funding to fully preserve the route
  system.
• Increasing use of BSTs in lieu of 45mm thick HMA
  overlayshowever overlays are still and will
  continue to be the preservation treatment of
  choice.
• How did we examine the efficacy of increased BST
  use?
• First, lets quickly look at HMA performance.

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Quick look at HMA Overlay Performance

• Performance for more recent (post Superpave)
  projects
• Rutting
• IRI
• Life by western and eastern Washington
• Projects placed between 1996 and 2001
• Evaluated with 2006 pavement condition survey
• Pavement age 5 to 10 years
• ½ inch HMA only
• 26 projects

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Average Performance
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Rutting
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Ride
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HMA Overlay Life

• Pavement life is also a function of
• Construction practices
• Specifications
• Material selection

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240,000 per lane-mile
21,000 per lane-mile
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Key Question
Could we save money by using BSTs on some roads
that are currently surfaced with HMA?

• What is the effect on the WSDOT preservation
  budget?
• What is the effect on long-term network
  performance?
• What is the effect on the traveling public?
• Further
• What is a reasonable upper level of AADT, at
  which BST resurfacings can be used?
• What is a reasonable upper level of annual ESALs
  at which BST resurfacings can be used?
• What combination of BST resurfacings and HMA
  overlays produce a cost effective rehabilitation
  strategy?

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HDM-4 (v2.03)The Highway Development and
Management System software

• Integrates multiple models in a unified analysis
• Economic
• Material
• Structural
• Condition
• UW and WSDOT has experience with HMD-4

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HDM-4 Modeling Observations

• Model may be biased towards existing trends
• The treatment strategy selected is highly
  dependent on the initial roughness
• The BST/HMA combination strategy is often
  selected regardless
• Not able to fine-tune the BST effects enough
• The HDM-4 model schedules a large number of
  treatments in the first year
• HDM-4 is difficult to master
• HDM-4 software support is almost non-existent.

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HDM-4 Estimated Roughness Conditions
AADT less than 8,000 and annual design lane ESALs
less than 40,000
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HDM-4 Results

• The NPV of all strategies are the same
• Increasing the use of BSTs appears to be
  economically feasible
• Agency expense and user costs increase over time
  for all strategies except the HMA overlay only
  option
• Reduced agency expenses will result in rougher
  pavements and higher user costs
• Higher BST use shifts cost from the agency to the
  user unless

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HDM-4 Conclusions

• HDM-4 is of limited but some use.
• Routes with AADT gt 2,000 are viable for BSTs.
• Considering more BSTs is not a mistake.
• The cost of maintaining a road network is largely
  a zero-sum game.

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Overall Assessment (1)

• Analyses via HDM-4 showed that more lane-miles of
  BST OK from a NPV view. ADT criterion increases
  from 2,000 to 4,000-5,000.
• WSDOT Pavement Policy has been changed to reflect
  this.
• Andthere physically is no ADT limit for BSTs.
• More BSTs will likely increase the IRI on the
  route system but by a limited amount (cycles of
  BST/HMA overlays, level-up quantities, etc, limit
  IRI increases).
• BSTs will rarely be used through towns and cities
  or at major intersections.

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Overall Assessment (2)

• Performance in Washington State
• BSTs apparently exceed typical national stats.
• HMA at or above national stats. Differences
  between western and eastern Washington need to be
  reduced.
• Does WSDOT need more pavement preservation funds?
• Of coursebut how much?
• Likely something close to 10,000/lane-mile/year.

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Overall Assessment (3)

• Is WSDOT likely to get that much pavement
  preservation funding anytime soonNO.
• So what can be done?
• Tweak the mix of BST and HMA overlays (in
  progress).
• Maximize quality of both hence performance life.
• Monitor carefully via PMS.
• Dont do anymore HDM-4 analyses!

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Thanks for you attention
Questions?
Contributors include Steve Muench, UW and Linda
Pierce, WSDOT