Performance Based Specifications

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Ultra Thin Whitetopping (UTW)

• Thin layer (50-100mm) of PCC concrete over an
  existing distressed AC pavement
• Similar to mill/inlay
• Bond developed between AC and PCC forming a
  composite pavement
• PCC is usually high early strength and fiber
  reinforced.
• Joint spacing is much shorter (1-3m)
• Requires thick underlying AC

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Contents

• Study Background
• Scope of the Study
• Life-cycle Cost Methodology
• Analysis Sites - Data set
• Parametric Data
• Pavement performance models, user costs,
  treatments, trigger limits, discount rate
• Results
• Conclusions

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How the Study Came About

• BC Redimix Association
• Had heard of the UTW technology and wanted to
  know if it could be used in the lower mainland
• City of Surrey
• Was interested in knowing if UTW would be a
  viable strategy in Surrey
• Canadian Portland Cement Association
• Agreed to fund a study

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Scope of the UTW Study

• Identify sites thought to be suitable candidates
  for UTW (intersections prone to rutting, AC
  thickness greater than 120mm)
• Assemble data (traffic geometry, structure,
  construction and performance history)
• Assemble parametric information (available
  treatments, rehab strategies, user costs,
  pavement performance models, discount rates
• Conduct LCC analysis
• Report on effectiveness of UTW vs other strategies

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Study Methodology

• Life-cycle Benefit/Cost for infrastructure
  preservation planning

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Life-cycle Cost

• Total Present Value (P.V.) of all costs over the
  on-going life of the pavement
• Life-cycle cost Initial Construction
  Costs
• P.V. Rehabilitation Costs
• P.V. Maintenance Costs
• P.V User Costs
• - P.V. Salvage costs

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Life-cycle costs for Preserving existing pavements

• Life cycle costspv
• P.V. Rehabilitation Costs
• P.V. Maintenance Costs
• P.V. User Costs
• (the analysis period is made long enough that the
  salvage value is exhausted - 50 years)

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Pavement Preservation Rehabilitation and
Maintenance Treatments

• Crack Sealing
• Patching
• UTW 50mm/80mm/100mm
• Overlay
• Reclaim
• Reconstruction

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Treatment application timing is a variable
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Pavement Strategies

• Strategy is comprised of combinations of
  individual treatments and treatment application
  timings
• Therefore, for a given site there are dozens of
  potential strategies.

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Example Pavement Strategies(combinations of
treatments)
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Two methods of determining User Costs Savings
(benefits)

• Measure User Costs Directly (with Road User Cost
  Models)
• Vehicle Operating cost models
• Delay Cost Models
• Accident Cost Models
• Measure User Costs Indirectly (by measuring the
  Area Under a Performance Curve)

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Direct Measurement of User Costs
Vehicle Repair costs Roughness Fuel
Consumption Roughness Delay Costs
Treatment application rate, Detour
Length
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RUCdo-nothing - RUCstrat 1 RUCBenefit strat 1
Calculating Strategy Benefits Using RUC
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Area-Under the-Curve Methodof measuring strategy
benefits
Calculating Strategy Benefits Using AUC
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List of Strategies (cost benefit)
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Strategy Costs are Compared with benefits to
measure cost effectiveness
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5 Methods of Defining Cost Effectiveness

• Minimum LCC called Total Transport Cost (TTC)
• Minimum of (rehab Maintenance user costs)
• B/C
• (RUCdo-nothing - RUCstrategy) / (rehab maint
  costs)
• Min Cost (to meet Performance Specification)
• Minimum of (rehab Maint) (ie. ignore
  benefit to minimize cost)
• Maximum AUC Benefit
• Maximize the Area under the performance curve
  (ignore cost to maximize benefit)
• Maximum AUC B/C
• AUC / (rehab Maint)

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Cost Effectiveness ( using RUC)
Max Benefit/Cost
.
Min PV Cost
Min TTC
Worst First
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Cost Effectiveness (using AUC)
Max Benefit/Cost
Maximum Benefit
Min PV Cost
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Common Policies for selection of effectiveness
measurement method

• Worst First (used in the absence of preservation
  planning)
• Minimum total LCC (TCC) - (minimizes total cost
  to the economy)
• Max benefit/cost - used when funding is severely
  constrained (attempts to provide best public bang
  for the tax buck)
• Minimum PV Cost to meet performance based
  objectives (used with performance based specs
  such as in Australian/New Zealand Maintenance
  Contracts)
• Maximum Benefit - Minimizes delay costs
  (ignoring direct agency costs).

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Analysis Data Set Requirements

• Site data affecting pavement performance
• subgrade, pavement structure, traffic volumes,
  vehicle loadings, climate and construction
  history
• Site data affecting Road User Costs
• traffic volumes and mix, intersection
  configuration, and/or detour lengths
• Site data required for calibrating pavement
  performance prediction models
• rutting history, roughness history, cracking
  history

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City of Surrey Supplied

• Existing AC thickness is the most important
  consideration for UTW
• Surrey has an extensive pavement thickness
  database
• selected 150 arterial and collector intersections
  with AC thickness greater than 120mm
• Historical roughness, rutting and cracking data
• Locally calibrated RUC models
• Locally calibrated pavement performance models
• 1999 Traffic AADT Volume Data, 1995
  Classification data

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Parametric Data Requirements

• pavement performance models
• Asphalt
• UTW
• set of potential treatments and costs
• maintenance treatments
• rehab treatments
• treatment trigger limits
• potential strategies
• combinations of treatments required to preserve
  the pavement indefinitely
• road user cost models
• discount rate

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Performance Prediction Models
Crack Strength, Traffic, Age Rut
Crack, Strength, Traffic,
Age Roughness Rut, Crack, Strength,
Traffic, Age, Environment
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Example Crack Prediction Model
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Example Rut Prediction Model
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Example Roughness Prediction Model
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Pavement Quality Index (PQI)(Composite Index for
AUC Calculations)
Overall Condition of the pavement Cond. Index
Roughness, Cracking, Rut etc. This Index is used
extensively in BC
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Overall Pavement Quality
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Rehabilitation Treatments and Costs (Can)

• For intersections in Surrey (weekend work, all
  inclusive)
• Reconstruction 50/m2
• Mill/Inlay 50mm 18/m2
• Deep Patch (prior to inlay) 13-55/m2
• 100mm UTW 45/m2
• 80mm UTW 40/m2
• 50mm UTW 37/m2

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Maintenance Treatments and Costs

• Crack Sealing 1.50/ln-m
• Route Seal Cracks 2.50/ln-m
• Thin Overlay/Patching 8/m2

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Treatment Triggers/Limits

• Reconstruction rutting (20 - 40mm) cracking (
  gt 20)
• Mill/Inlay rutting (20 - 40mm) cracking ( 5 -
  25)
• UTW rutting (20 - 40mm) cracking ( 5 - 40 )
• Crack Seal All low severity cracks every 3
  years
• Route Seal All medium severity cracks every 3
  years
• Patching All high severity cracks every 3 years

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Predicted Cracking - Overlay in 2004
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Predicted Rut - Overlay in 2004
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Predicted Roughness - Overlay 2004
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Overall Pavement Condition - Overlay in 2004
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Reconstruct - 2008
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Reconstruct - 2009
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Reconstruct - 2010
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UTW Pavement Performance Models

• Inferred from UTW design charts
• provide design life in terms of allowable trucks
  to the end of design life
• PCC industry claims
• very little load related cracking or rutting
  until the end of the design life
• Assumed that at the end of the design life the
  pavement deteriorates at the rate of the
  remaining underling AC (which is now thinner)

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UTW - 2004
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UTW - 2004
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UTW - 2004
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UTW - 2004
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UTW - 2005
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UTW - 2006
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UTW - 2007
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Road User Cost Models

• Vehicle Operating Costs (models are available)
• Fuel Consumption
• Vehicle Repair and parts consumption
• Delay Costs (no readily available models)
• Freight Rates
• Value of Commercial Time
• Value of Personal Time
• Idling Fuel Consumption
• Detour Costs (more easily calculated than delay
  costs)
• Fuel Consumption
• Vehicle Repair and parts consumption
• Amortization, Insurance etc.

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VOC Model Used
Surrey Model
Ontario Model
58 of Ontario
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VOC models used
Ontario Model
58 of Ontario
Surrey Model
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Delay Costs (not used)

• Most Significant Cost
• at 5/car/hr and 10/truck/hr a 30 min delay over
  two days at major intersection could cost as much
  as 500K
• Difficult to agree on
• Longer life treatments such as PCC or
  reconstruction are heavily favoured
• Therefore the study assumed that all traffic
  would be detoured.

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Detour Costs

• Detour Length 1.6 km (Surrey Arterial grid)
• VOC
• 0.35/car/km
• 1.00/truck/km
• Off-peak Closure Period
• Reconstruction 4 days
• UTW 2 days
• Mill/inlay 1 day

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4 6 Discount Rate

• 4 is the long term difference between B of
  Canada prime and Inflation
• 4 is used by BC Alberta Governments
• NWT uses 6
• Ontario uses 7
• Arguably should use greater than 4 to allow for
  future lower costs resulting from new technology

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The Analysis

• Used Deighton Associates Limited - Total
  Infrastructure Management System (dTIMS) LCC
  analysis software
• Tested 150 intersections
• Approximately 44 strategies/intersection
• Cost effectiveness of 6,600 strategies measured
  by each of the 5 cost effectiveness methods

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The Results

• The strategy selected is heavily dependant on the
  cost effectiveness method used
• It is impossible to have exactly the same
  strategy selected by all methods
• It is possible to have a strategy comprised of
  the same underlying treatment (applied in
  different years perhaps) selected by all 5
  methods
• example at a given intersection
• 50mm UTW lowest cost
• 100mm UTW Max AUC
• 75mm UTW Max B/C

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UTW Effectiveness
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Example Effects of selection criteria on a
network of pavements
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The bad news

• Hard to find thick pavements
• Of the 36 sites where UTW is most effective, only
  2 are warranted to be done in 2000/2001
• The AC thickness must be uniform ie. Continuously
  thick (additional pavement thickness survey cost)
• UTW is less compatible (than AC) with future
  geometric changes

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