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Enhancement of the Pavement Health Track (PHT) Analysis Tool Final Report

Maintenance Cost Model

Introduction

With aging of highway pavements in the nation and increasingly limited funding for maintenance activities, state highway agencies, metropolitan transportation organizations, and other local transportation agencies are increasingly looking to using available funding available for highway construction and maintenance as efficiently as possible. Efficiency in this context implies getting the most in terms of pavement health for every investment made on their highway pavement corridors or networks. One way of increasing efficiency is the adoption of pavement preventive maintenance improvements in addition to the more intensive rehabilitation and reconstruction improvements as part of pavement management.

Preventive maintenance (PM) has been described as a planned strategy of cost-effective maintenance activities applied to an existing highway pavement that preserves the pavement health, retards the rate of future deterioration, and improves pavement functional condition without significantly increasing structural capacity.

PM improvements are significantly cheaper options for agencies with limited budgets. Research has demonstrated that PM improvements, when applied in a timely manner do prevent or delay onset of significant deterioration thereby prolonging pavement service life. Although more expensive rehabilitation and reconstruction improvements must be performed eventually on all pavements, costly rehabilitation or reconstruction can be delayed with timely PM improvements. Delaying PM improvements increases the extent of pavement deterioration leading to higher future rehabilitation and reconstruction costs.

The PHT analysis tool does not consider the effect of maintenance or rehabilitation treatments when forecasting future pavement distress and smoothness, and thus it uses the do-nothing approach to estimate RSL. The objective of this task was to develop a model to account for the effect of maintenance activities in characterizing pavement health and on the RSL predictions and the associated budgetary needs. Another equally important objective was to incorporate into the PHT Tool the ability to identify deficient pavement sections, identify feasible/preferred treatment options, and prioritize needed improvements according to predetermined budgetary or performance constraints.

Maintenance Model

The PHT maintenance model estimates benefits of each pavement section improvement quantified in terms of the value added to the pavement infrastructure. Benefits are calculated based on the following assumptions:

  • Straight-line depreciation is used to depreciate individual pavement assets over their service life.
  • The post-treatment rate of depreciation remains the same.
  • The initial service life of the pavement is the sum of the current pavement age and the RSL where the current pavement age is the difference between the current year of record and the original year of construction for new pavements; or the year of last improvement for rehabilitated pavements.

Straight-line depreciation, along with the effect of the application of a maintenance treatment on increasing the service life and asset value, is shown in Figure 75.

A dimensionless line graph illustrates the features of straight-line depreciation. Depreciation Rate is shown as a downward slope from the Value axis, beginning at a point in time designated Original Construction or Rehabilitation, and ending at a point in time designated End Initial Service Life. This interval is termed initial service life. At some point along this slope, a Maintenance Treatment Application is plotted, which increases the value by an amount designated Increased Value Post-Treatment, and the slope now becomes the Resumed Depreciation, ending at a point in time designated the End Extended Service Life. The interval from the origin to this point is designated the Revised Value Post-Treatment.
Figure 75. Straight-Line Depreciation with Maintenance Treatment

The following equations described how the PHT maintenance model determines the overall cost and benefits of the application of a maintenance treatment.

Determine the initial service life of the pavement.

ISL = (CYR - OCYR) + RSL (New Pavement) (1)

ISL = (CYR - LIYR) + RSL (Rehabilitated Pavement)

Where:
ISL = Initial Service Life, years
CYR = Current Year, (field: year_record)
OCYR = Original Year of Construction, (field: year_last_construction)
LIYR = Year of Last Improvement, (field: year_last_improv)
RSL = Estimated Remaining Service Life, (field f_Overall_RSL_Years).

Estimate monetary benefit of the maintenance action for the highway section.

The term BENEFIT is equal to SLE multiplication operator open parenthesis open parenthesis begin fraction begin numerator NPAC multiplication operator beta end numerator over begin denominator ISL end denominator end fraction close parenthesis addition operator open parenthesis open parenthesis NPAC subtraction operator COSR close parenthesis multiplication operator DR close parenthesis close parenthesis multiplication operator open parenthesis LN multiplication operator LEN close parenthesis.

Where:
BENEFIT = Estimated Monetary Benefit
SLE = Service Life Extension, (see Table 18)
NPAC = New Pavement Asset Cost, (see Table 17)
ISL = Initial Service Life, (see Equation 1)
COST = Maintenance Cost, (see Table 17)
DR = Discount Rate
LEN = Length of the Highway Section, miles, (field: section_length)
LN = Number of Lanes, (field: through_lanes)
β = Adjustment Factor, (see Table 15).

Calculate the total cost of the maintenance action for the highway section.

COST = UCOST × (LEN × LN) (3)

Where:
COST = Estimated Cost of Improvements
UCOST = Unit Cost of Improvement per Lane-Mile, (see Table 17)
LEN = Length of the Highway Section, miles, (field: section_length)
LN = Number of Lanes, (field: through_lanes).

Calculate the Benefit-to-Cost Ratio.

The term BCR is equal to open parenthesis begin fraction begin numerator BENEFIT end numerator over begin denominator COST end denominator end fraction close parenthesis

Where:
BCR = Benefit to Cost Ratio
BENEFIT = Estimated Monetary Benefit, (see Equation 2)
COST = Estimated Cost of Improvements (see Equation 3).

Feasible maintenance treatments are established by pavement type and highway functional class and are described in Table 13 and Table 14.

Table 13. Description of Feasible AC Surfaced Pavement Treatments
PM Group General Description Applicable PM Actions Extent of Application Functional Class: Principal & Major Functional Class: Minor
1 Surface sealing
  • Chip seals & surface treatment (single & double)
  • Slurry seal
  • Microsurfacing
  • Hot in place recycling
  • Microsurfacing
100% of lane area   checkmark
2 Full depth patching with OR without grinding
  • Full depth AC patching (including base replacement)
  • Grinding & grooving
Patching as needed with 100% lane area sealing checkmark checkmark
3 Full depth patching with AC OL OR surface recycling*
  • Hot-in-place recycling
  • Microsurfacing
  • Ultra-thin HMA overlays (e.g., novachip)
  • Thin AC overlay
  • Mill & thin AC overlay
100% lane area checkmark  
4 Major Rehabilitation
  • Placement of thick 2- to 8-in AC overlay
100% lane area checkmark checkmark
5 Reconstruction
  • Reconstruct entire AC layer thickness only
100% lane area checkmark checkmark

Table 14. Description of Feasible JPCP Pavement Treatments
PM Group General Description Applicable PM Actions Extent of Application Functional Class: Principal & Major Functional Class: Minor
1 Functional repair
  • Full-depth concrete repair or slab replacement including slab jacking
  • Joint load transfer restoration (dowel bar retrofit & joint patching)
  • Diamond grinding & grooving
Up to 5% of lane area checkmark  
2 Surface seals & thin overlay*
  • Seals (surface sealing, slurry seal, & microsurfacing)
  • Thin HMA overlay
100% of lane area checkmark checkmark
3 Major rehabilitation
  • Placement of thick 2- to 8-in AC overlay OR unbonded PCC overlay
100% lane area checkmark checkmark
4 Reconstruction
  • Reconstruct entire AC/PCC layer thickness only
100% lane area checkmark checkmark

Each highway section is evaluated by the maintenance model to determine if it is a candidate for a feasible maintenance treatment. A flowchart of the PHT maintenance model algorithm is illustrated in Figure 76.

A flow chart in seven levels traces activities related to the PHT maintenance model. At the top level, information from maintenance trigger levels feeds into the activity to Evaluate Distress Levels and continues down to the next level, where information from maintenance feasibility levels feeds into the activity to Determine if Feasible Maintenance Option is Available. Continuing down, information from maintenance treatment costs feeds into the activity to Calculate Cost of Maintenance Treatment for the Highway Section an continues down to the next level, where information from service life extensions feeds in the activity to Determine Service Life Extension, and continues down to the activity to Calculate Monetary Benefit of Applying the Maintenance Treatment, and continues down to a decision point Constraint Option. For Funding constraint, flow proceeds laterally to the activity Prioritize by Criteria and Determine if Finding Is Available, and down to the final activity. For Minimum BCR constraint, flow proceeds laterally to the activity Determine if Maintenance Treatments Meets Minimum BCR Threshold, and down to the final activity. Information from post maintenance distress resets feeds into the final activity to Calculate Distress Resets After Application of Maintenance Treatment.
Figure 76. PHT Maintenance Model Flowchart

Adjustment Factors

The initial value of the pavement at original construction or rehabilitation is determined by the new construction costs multiplied by the adjustment factors shown in Table 15.

Table 15. Initial Pavement Value Adjustment Factors
Pavement Type HPMS Surface Type Adjustment Factor
New Pavement 2, 3, 4, 5 1.00
Rehabilitated Pavement, thin overlay 6, 7, 8, 9, 10, 11 0.60
Rehabilitated Pavement, thick overlay 6, 7, 8, 9, 10, 11 0.60

Lookup Tables

The maintenance model uses five lookup tables as shown in Table 16 through Table 20. These tables describe the default values used by the PHT maintenance as described below.

  • Trigger Levels. The trigger-level table provides the deficiency thresholds for each distress type that defines at what point a maintenance treatment is warranted. Any distress exceeding its threshold triggers the need for a maintenance action.
  • Feasibility Thresholds. The feasibility thresholds provide the decision criteria for selecting the improvement option based on the pavement distress and RSL. The preferred improvement will be the lowest feasible improvement group that will address the pavement's conditions.
  • Post-Maintenance Resets. The post-maintenance reset table provides the percentage of improvement for each distress type as a result of a maintenance treatment. The extent of the improvement is determined based on the existing distress level and the type of treatment applied. A value of 0% means no change to the distress while a value of 100% implies that the distress is reset to a like-new condition.
  • Service Life Extensions. The service life extension table provides the post-improvement extension to the RSL (years) as a result of the application of a maintenance treatment. Additional extensions to the service life are provided to take into account the effect of climate and traffic conditions and pavement construction.
  • Treatment Costs. The treatment cost table provides the estimated cost of applying a maintenance treatment as measured in current dollars per lane-mile.

The model will select a preferred treatment strategy from the list in Table 19 and Table 20 based on each option's selection criteria. The model will select the lowest feasible improvement group by order of severity that will address the distress/IRI and RSL conditions.

Table 16. Default Maintenance Trigger Levels
Surface Type Class IRI Cracking Percent Cracking Length Rutting Faulting
Flexible, Composite Interstate 80 0 % 250 ft/mi 0.25 in.  
Flexible, Composite Primary 100 0 % 1000 ft/mi 0.25 in.  
Flexible, Composite Secondary 125 5 % 1000 ft/mi 0.25 in.  
Rigid Interstate 100 0 %     0.10 in.
Rigid Primary 100 0 %     0.10 in.
Rigid Secondary 125 0 %     0.15 in.

Table 17. Default Post-Maintenance Resets (%) and Treatment Costs
Surface Type Treatment IRI Cracking Percent Cracking Length Rutting Faulting Cost per Lane-Mile
Flexible, Composite Surface Sealing 0 % 40 % 15 % 10 %   $ 12,250
Flexible, Composite Full-Depth Patching 0 % 40 % 15 % 25 %   $ 32,500
Flexible, Composite Patching and Overlay 30 % 100 % 90 % 50 %   $ 42,000
Flexible, Composite Rehabilitation 100 % 100 % 100 % 100 %   $ 92,000
Flexible, Composite New / Reconstruction 100 % 100 % 100 % 100 %   $ 290,000
Rigid Functional Repair 50 % 7 %     70 % $ 27,750
Rigid Seal and Overlay 0 % 0 %     0 % $ 22,000
Rigid Rehabilitation 0 % 0 %     0 % $ 132,750
Rigid New / Reconstruction 100 % 100 %     100 % $ 450,000
Note: A value of 0% means no change while a value of 100% implies reset to like-new conditions.

Table 18. Default Service Life Extensions (Years)
Surface Type Treatment RSL Extension Additive (+)
Climate (non-freeze)
Additive (+)
Climate (dry)
Additive (+)
Class (non-principal)
Additive (+)
Pavement (composite)
Additive (+)
Sub-Grade (fine)
Flexible, Composite Surface Sealing 1.5          
Flexible, Composite Full-Depth Patching 0.5 1   2 0 0
Flexible, Composite Patching and Overlay 5.5 0   0 0 0
Flexible, Composite Rehabilitation 10 2.5   2 5 3
Flexible, Composite Reconstruction 20          
Rigid Functional Repair 6 1 2 0   0
Rigid Seal and Overlay 5.5          
Rigid Rehabilitation 15          
Rigid Reconstruction 30          

Table 19. Feasible Improvements for Flexible and Composite (AC) Pavements
  Interstate Primary Secondary
Surface sealing N/A N/A RSL > 5 years
Rutting < 0.35 in
Cracking Length < 2500
Cracking Percent < 5 %
IRI < 150 in/mi
Full depth patching with OR without grinding RSL > 10 years
Rutting < 0.25 in
Cracking Length < 250
Cracking Percent < 5 %
IRI < 125 in/mi
RSL > 5 years
Rutting < 0.25 in
Cracking Length < 1000
Cracking Percent < 5 %
IRI < 150 in/mi
RSL > 5 years
Rutting < 0.35 in
Cracking Length < 1000
Cracking Percent < 5 %
IRI < 125 in/mi
Full depth patching with thin AC overlay OR surface recycling RSL > 10 years
Rutting < 0.35 in
Cracking Length < 1000
Cracking Percent < 10 %
IRI < 125 in/mi
RSL > 5 years
Rutting < 0. 5 in
Cracking Length < 2000
Cracking Percent < 10 %
IRI < 150 in/mi
N/A
Major rehabilitation RSL > 3 years
Rutting < 0.35 in
Cracking Length < 2000
Cracking Percent < 15 %
IRI < 150 in/mi
RSL > 3 years
Rutting < 0.5 in
Cracking Length < 2000
Cracking Percent < 15 %
IRI < 150 in/mi
RSL > 3 years
Rutting < 0.75 in
Cracking Length < 2500
Cracking Percent < 15 %
IRI < 175 in/mi
New or reconstruction RSL < 3 years
Rutting > 0.35 in
Cracking Length > 2000
Cracking Percent > 15 %
IRI > 150 in/mi
RSL < 3 years
Rutting > 0.5 in
Cracking Length > 2000
Cracking Percent > 15 %
IRI > 150 in/mi
RSL < 3 years
Rutting > 0.75 in
Cracking Length > 2500
Cracking Percent > 15 %
IRI > 175 in/mi

Table 20. Feasible Improvements for Rigid Pavements
  Interstate Primary Secondary
Functional repair RSL > 10 yrs
Cracking Percent < 10%
Faulting < 0.15 in
IRI < 125 in/mi
RSL > 10 yrs
Cracking Percent < 10%
Faulting < 0.15 in
IRI < 125 in/mi
N/A
Surface seals & thin overlay RSL > 10 yrs
Cracking Percent < 1%
Faulting < 0.1 in
IRI < 150 in/mi
RSL > 10 yrs
Cracking Percent < 1%
Faulting < 0.1 in
IRI < 150 in/mi
RSL > 10 yrs
Cracking Percent < 1%
Faulting < 0.1 in
IRI < 150 in/mi
Major rehabilitation RSL > 5 yrs
Cracking Percent < 15%
Faulting < 0.2 in
IRI < 175 in/mi
RSL > 5 yrs
Cracking Percent < 15%
Faulting < 0.2 in
IRI < 175 in/mi
RSL > 5 yrs
Cracking Percent < 20%
Faulting < 0.2 in
IRI < 175 in/mi
Reconstruction RSL < 5 yrs
Cracking Percent > 15%
Faulting > 0.2 in
IRI > 175 in/mi
RSL < 5 yrs
Cracking Percent > 15%
Faulting > 0.2 in
IRI > 175 in/mi
RSL < 5 yrs
Cracking Percent > 20%
Faulting > 0.2 in
IRI > 175 in/mi

Graphical User Interface

The PHT maintenance model is implemented into the PHT graphical user interface as an integrated feature of the PHT results viewer window. The Maintenance tab in the vertical panel provides access to the PHT maintenance model as shown in Figure 77.

A screen shot sows the Maintenance tab of the PHT Maintenance Model tool, where the user can input values for minimum benefit/cost ratio, constraints, and discount rate, and access information related to lookup tables, trigger levels, feasibility thresholds, post maintenance resets, service life extensions, and treatment costs.
Figure 77. PHT Maintenance Model User Interface

There are two objectives for the maintenance model:

  • Minimum Benefit/Cost Ratio (BCR). This objective will identify all highway sections that have a feasible maintenance treatment option available that will produce a benefit/cost ratio greater than some specified level regardless of cost.
  • Constrained by Funds. This objective will identify all highway sections that have a feasible maintenance treatment option available and prioritize each until some specified level of funding has been exhausted. Prioritization is performed using one of three selection methods:
    • Worst RSL. This method selects as the first to be treated those highway sections that have the lowest RSL as forecasted by the PHT analysis.
    • Maximized BCR. This method selects as the first to be treated highway sections that have a maintenance treatment option that will produce the highest BCR.
    • Best RSL Extension. This method selects as the first to be treated those highway sections that have a maintenance treatment option that will produce the highest service life extension.

The discount rate percentage is used by the maintenance analysis for estimating the benefits associated with postponing reconstruction costs by performing a less expensive maintenance treatment to prolong the life of the existing pavement.

The results of the PHT maintenance model analysis provide the following information:

  • Maintenance Option. Recommended maintenance treatment for the highway section.
  • Service Life Extension. The extension in service life of the pavement as a result of applying the recommended maintenance treatment.
  • Maintenance Cost. Overall total cost of applying the recommended maintenance treatment taking into account the length of the highway section and the number of lanes treated.
  • Overall Benefit. Benefit, quantified in terms of the value added to the pavement infrastructure due to the application of a given maintenance treatment.
  • Benefit/Cost Ratio. Ratio of the overall benefit and total maintenance cost.
  • Revised Distresses. The revised post-maintenance distress values for IRI, rutting, cracking, and faulting as a result of applying the recommended maintenance treatment.
Updated: 11/22/2013