Improving Rehabilitation Selection for Pavement Life Cycle Cost Analysis ACPA Mid Year Meeting Applying Life Cycle Cost Analysis for Fair Pavement Type Selection Workshop June 24, 2014 Jim Mack, PE, MBA jameswmack@cemexcom
LIFE CYCLE COST ANALYSIS IS PROJECT ANALYSIS TOOL THAT QUANTIFIES THE TOTAL COSTS OF OWNERSHIP Accounts for initial costs and discounted future rehabilitation costs Pavement Condition Ownership Costs Good Poor Initial Cost Rehab Rehab Min Acceptable Rating Time or Traffic Rehabilitation Cost Salvage Value LCCA compares different options for a given project and determines which pavement design is most cost effective over the analysis period Years NNN = IIIIIII CCCt + RRRRR cccc 1 1 + d n SSSSSSS VVVVV k 1 1 + d n k Where NPV = Net Present Value d = real discount rate = year of expenditure n k - 2 -
WHILE PARTIES AGREE ON THE PROCESS, THERE IS DISAGREEMENT AND LACK OF TRUST IN THE RESULTS Arguments are about the correctness of the inputs Pavement Condition Good Poor Rehab Min Acceptable Rating Rehab Sources of Uncertainty & Variability 1 Temporal - Timing of Rehabilitation Activities - Historical vs Predicted 2 Scenario - What rehabilitation activities are done Time or Traffic - Preservation Options - Overlay Options Ownership Costs Initial Cost Years Rehabilitation Cost 2% - 10% FDR & DG 2 to 4 AC Overlay Mill & Overlay Rubb / AC overlay Unbonded OL Mill & Overlay Rubb / AC overlay Unbonded OL Reconstruction Salvage Value 3 Measurement - Cost - Inflation - Price Adjustment Clauses - Unit Price - Material Quantities - Bidding Practices (Incentives and Disincentives, SY vs Tons, etc) Goal is to make sure Uncertainty & Variability are treated similarly so that Risk Assumptions in the LCCA are balanced - 3 -
WHEN DETERMINING REHABILITATION TIMING Need to develop reasonable performance period for each activity based on the Given Design Pavement Condition Ownership Costs Good Rehab Rehab Poor Min Acceptable Rating Time or Traffic Initial Cost Rehabilitation Cost Initial Performance Period Salvage Value Performance periods describe the length of time from one pavement construction activity to the next Initial performance period - Time from initial construction till the pavement undergoes its first rehabilitation Rehabilitation performance period - Time between two consecutive rehabilitation activities (eg patching, asphalt overlays, etc) Years Rehab 1 Performance Period Rehab 2 Performance Period - 4 -
AGENDA Initial Performance Period Rehabilitation Performance Periods Rehabilitation Selection - 5 -
INITIAL PERFORMANCE PERIOD USED BY STATE DOTS Based on History or Pavement Design Life Asphalt Pavements Concrete Pavements 50 Time to First Rehabilitation Red lines show the range of values for states that do not have fixed value 50 Time to 1 st Rehab (years) 12 10 15 12 17 10 20 20 15 18 CO GA KS KY NC PA TN AL AR DE MS OH VA NY SC UT WA FL MD AR LA MN NJ ME HI NE VT WI MT CA IL MO NV NH OR RI WY IN MI 45 40 35 30 25 20 15 10 5 Max 26 Min 10 Avg 154 Max 40 Min 10 Avg 221 25 25 20 22 30 20 45 40 35 30 25 20 15 10 5 VA AR NY MI MN WI AL FL GA IL KS MD MT SC UT VT WY CO OH MO WA MI IN NJ NC NE CA 1 2007 National LCCA Survey by Mississippi DOT 2 National LCCA Survey Conducted by South Carolina DOT 3 State DOT Pavement Design and/or Pavement Type Selection Manuals - 6 -
WHEN USING HISTORICAL PERFORMANCE Need to be aware that design features impact the pavement performance Average Time to First Major Rehabilitation of Concrete Pavement in Georgia 1 Year 20 Time to 1 st Rehab in LCCA 2 17 29 29 21 14 29+ 33 25 No Section has reached a major rehabilitation 54% of system reviewed is made up of these pavements 10 22% of pavements reviewed 24% of pavements reviewed These pavements have not needed any major rehabilitation Insufficient data to perform an analysis (oldest sections are ~20 years) Non-doweled JPCP (20+ ft jts) on soil / soil Cement (circa 1960's) Non-doweled JPCP (20+ ft jts) on GAB (circa early 1970's) Doweled JPCP (20-ft jts) on GAB (circa late 1970-80's) Doweled JPCP (15-ft jts & 13-ft WL) on AC Base over GAB (circa 1990+) Historical performance must be based on data from like roadways to avoid biasing the results 1 Georgia Concrete Pavement Performance and Longevity, Final Report, GDOT Research Project No 10-10, Task Order No 02-74 Dr James (Yichang) Tsai, PE, Yiching Wu, Chieh (Ross) Wang, Georgia Institute of Technology, February 2012 Note: Overall Avg Time to 1st Rehab = 17 years Projects carried 17-30 million ESALs, which is 2-4 times the designed ESALs, before 1 st rehabilitation 2 Time to 1 st Rehabilitation in GDOT LCCA procedure = 20 years, time to 2 nd Rehabilitation = 40 years Features - 7 -
PAVEMENT ME PERFORMANCE PREDICTIONS DEFINE INITIAL PERFORMANCE PERIODS Predicted Time Range for First Rehabilitation Design Life (Rehab Required) As move Time to first Rehab across predicted time range, category of repair changes (in order): 1 Concrete Pavement Preservation 2 Overlays 3 Reconstruction Amount to repair Red Line - Defined Distress Limit When major rehabilitation is needed (ie patching & DG or overlay) Black Dashed Line - The actual (most likely) level of distresses predicted Blue Dotted Line - The predicted distresses at the given reliability level (ie 90%) Designs are based on when this line hits the defined distress limit Design life is when the Blue Reliability curve hits red Predefined Distress level - 8 -
PAVEMENT-ME PROVIDES A PROCESS TO COMPARE DIFFERENT DESIGNS / DIFFERENT FEATURES Standard Design Optimized Design 80 JPCP w/ Dowels Spacing = 15 ft 80 JPCP w/ Dowels Spacing = 12 ft Rehab Target 30 AC Base (SuperPave 190) 12 Graded Agg Base Course 6 Graded Agg Base Course Optimized ~ 24 Yr to 1 st Rehab Standard ~ 24 Yr to 1 st Rehab AASHTO Class A-7-5 AASHTO Class A-7-5 Pavement-ME helps identifies Design Risks so the designer can mitigate their impacts - 9 -
REHABILITATION TIMING SHOULD BE BASED ON BOTH MODELED PERFORMANCE & HISTORY Modeling Percent Slabs Cracked, % 50 40 30 20 10 0 85" UBOL -13' JS (CTE=60) Predicted Cracking 85" UBOL -13' JS (CTE=60) - 90% Reliability Distress Limit Rehab Required 0 4 8 12 16 20 24 28 32 36 40 44 48 52 Pavement-ME range of timing to 1 st Rehab Pavement-ME predicted performance Provides predicted performance of major structural distress Allows for comparison of design features History JPCP = ~30 to 39 years 0 4 8 12 16 20 24 28 32 36 40 44 48 52 Pavement-ME does not Predict all Distress Use Historical Data for other potential distresses Final Timing Pavement Costs Initial Construction Costs Yr 35 1 st Rehab Patch & DG 0 4 8 12 16 20 24 28 32 36 40 44 48 52 Range for 1 st Rehab Result: When used together, can minimize structural distress and while accounting for other non- Pavement-ME distresses Pavement Age (years) Proposed Concrete Rehabilitation Schedules for ALDOT LCCA Procedures - 10 -
AGENDA Initial Performance Period Rehabilitation Performance Periods Rehabilitation Selection - 11 -
REHABILITATION PERFORMANCE PERIOD USED BY STATE DOTS Asphalt Pavements Concrete Pavements 50 Age at 1 st Rehabilitation Age at 2 nd Rehabilitation Age at 3 rd Rehabilitation Age at 4 th Rehabilitation 50 Time to 1 st Rehab (years) 45 40 35 30 25 45 40 35 30 25 20 15 20 15 10 5 Init R-1 R-2 R-3 Max 26 20 13 12 Min 10 5 8 5 Avg 154 114 105 85 CO GA KS KY NC PA TN AL AR DE MS OH VA NY SC UT WA FL MD AR LA MN NJ ME HI NE VT WI MT CA IL MO NV NH OR RI WY IN MI AL Init R-1 R-2 Max 40 20 10 Min 10 5 10 Avg 221 129 100 10 5 VA AR NY MI MN WI AL FL GA IL KS MD MT SC UT VT WY CO OH MO WA MI IN NJ NC NE CA 1 2007 National LCCA Survey by Mississippi DOT 2 National LCCA Survey Conducted by South Carolina DOT 3 State DOT Pavement Design and/or Pavement Type Selection Manuals - 12 -
A COMMON PRACTICE IS TO USE A STANDARD REHABILITATION ACTIVITY AND TIMEFRAME Pavement condition vs age 100 80 Condition 60 40 20 0 0 10 20 30 40 50 60 Time, years Source: ACI Seminar on Performance-Specification for Concrete, Tom Yu, Federal Highway Administration, National Concrete Consortium (NCC) Meeting, Jacksonville FL, April 24, 2014-13 -
INCREASING TRAFFIC AND DAMAGE MEANS THAT REHABILITATION TIMING DECREASES Pavement condition vs age Actual Performance Source: ACI Seminar on Performance-Specification for Concrete, Tom Yu, Federal Highway Administration, National Concrete Consortium (NCC) Meeting, Jacksonville FL, April 24, 2014-14 -
THERE ARE 3 WAYS TO ESTIMATE REHABILITATION PERFORMANCE Procedures 1 Assume all rehabilitation activities carry the same amount of traffic as the original pavement Simple to use Can not distinguish long term impacts of design features 2 Adjust Pavement-ME performance curves for the amount of distress repaired and assume that performance curves follow the same curve prior to the rehabilitation Gives reasonable answers and does not require additional Pavement-ME runs Good for preservation activities It can not account for the changes in structural capacity (increase of decrease of thickness) Run Pavement-ME to evaluate the performance of rehabilitated pavements using the predicted condition and increased traffic levels The most rigorous procedure Can account for structural changes 3-15 -
DETERMINING PERFORMANCE FOR REHABILITATION ACTIVITIES Procedure 1 - Using Traffic Counts 1 Estimate life of the original pavement 2 Determine how many vehicles are carried in that time 3 Assume that each major rehabilitation will carry that same amount of traffic 4 Determine life of each rehabilitation by matching traffic Rehab Target Optimized ~ 24 Yr to 1 st Rehab Standard ~ 24 Yr to 1 st Rehab Example Original Pavement is predicted to 24 years - Carries 30 million trucks - Growth is 3% To carry the next 3 million trucks takes 12 years - Rehab year = 36 To carry 3 rd 3 million trucks takes 8 years - Rehab year = 44 Truck Traffic 14,000,000 12,000,000 10,000,000 8,000,000 6,000,000 4,000,000 2,000,000 Initial Rehab 1 Rehab 2 Rehab 3 0 0 4 8 12 16 20 24 28 32 36 40 44 48 52 Year - 16 -
DETERMINING PERFORMANCE FOR REHABILITATION ACTIVITIES Procedure 2: Adjust Performance Curves 1 When curve hits predefined distress, repair pavement to original condition (IRI = 70 in/mile) 2 Assume new, adjusted curve follows same slope of the original curve 3 When adjusted curve hits predefined distress again, repair pavement 4 Continue repeating the process thru analysis period Adjusted Pavement-ME Performance Curves with Rehabs Original Rehab Adjusted DD RRR = D o + D RRR D RRR 1 DD RRR D o D RRR = Adjusted Distress Level at any time after rehabilitation = Starting Distress Level = Predicted Distress Level from original Pavement-ME Curve D RRR 1 = Distress Level at time of rehabilitation (amount of repair) Original 8 JPCP / 3 AC / 12 Agg CPP 1 = 25 Yrs CPP 2 = 37 Yrs (Crack) CPP 3 = 43 Yrs (Crack) Optimized 8 JPCP / 6 Agg 12 JS CPP 1 = 25 Yrs CPP 2 = 41 Yrs Results are Similar running Pavement-ME (but much easier to do) Can account for variation in sensitivity analysis - 17 -
DETERMINING PERFORMANCE FOR REHABILITATION ACTIVITIES Procedure 2: Adjust Performance Curves Predicted Faulting Predicted Cracking Performance criteria is 20-year faulting below 012 inches Performance criteria is 20-year cracking below 10% of slabs Controlling Distress for rehabilitation timing switched from IRI to Cracking - 18 -
DETERMINING PERFORMANCE FOR REHABILITATION ACTIVITIES Procedure 3: Run Pavement-ME in Rehabilitation Mode for each additional Activity Combined Pavement-ME Performance Curves with Rehabs 1 When curve hits predefined distress, record traffic and distress values 2 Run Pavement-ME in Rehabilitation Mode for the remaining years in the analysis period (eg 25 years) Update traffic Add rehabilitation activities 3 When adjusted curve hits predefined distress again, record traffic and distress values and repeat 4 continue repeating the process thru analysis period Positives Rigorous Can account for thickness change Can do overlays Problems Requires great care to make sure all inputs match (traffic, bonding, materials, etc) Original 8 JPCP / 3 AC / 12 Agg CPP 1 = 25 Yrs CPP 2 = 38 Yrs (crack) CPP3 = 45 Yrs (crack) Original Rehab Adjusted Optimized 8 JPCP / 6 Agg 12 JS CPP 1 = 25 Yrs CPP 2 = 43 Yrs Time between rehabilitation changes with designs and decreases due to increasing traffic - 19 -
DETERMINING PERFORMANCE FOR REHABILITATION ACTIVITIES Procedure 3: Run Pavement-ME in Rehabilitation Mode for each additional Activity Predicted Faulting Predicted Cracking Performance criteria is 20-year faulting below 012 inches Performance criteria is 20-year cracking below 10% of slabs 1 st Rehabilitation was controlled by IRI, 2 nd Rehabilitation controlled by Cracking - 20 -
COMPARISON OF REHABILITATION PERFORMANCE USING THE DOT STANDARD POLICY VS PAVEMENT-ME PREDICTIONS Pavement-ME Adjust Performance Curves Run Pavement-ME in Rehab Mode Standard DOT Policy Based on Same Traffic Standard Optimized Standard Optimized Initial Const Yr 0 Yr 0 Yr 0 Yr 0 Yr 0 Yr 0 Rehab 1 20 24 24 24 24 24 Rehab 2 40 36 36 41 38 43 Rehab 3 44 43 45 Using Pavement-ME accounts for the performance / activities for a Given Design, which creates more realistic LCCA s for comparison - 21 -
WHEN COMPARING ALTERNATIVES, RISK ASSUMPTIONS FOR REHABILITATION TIMING NEEDS TO BE SIMILAR Concrete Pavement Costs Initial Construction Costs Schedule Yr 35: Rehab 1 - Patch & DG Yr 45: Rehab 2 - Patch & DG Rehab 1 Range for 1 st Rehab Rehab 2 Analysis Period Range for 2 nd Rehab Age (yrs) 0 4 8 12 16 20 24 28 32 36 40 44 48 52 Concrete Designs have Less Risk on Rehabilitation Timing Asphalt Pavement Costs Initial Construction Costs Rehab 1 Range for 1 st Rehab Preserv 1 Rehab 2 Range for 2 nd Rehab Preserv 2 Analysis Period Schedule Yr 19: Pres 1 - Crack Seal Yr 24: Rehab 1 - Mill & Fill Yr 375: Pres 2 Microsurface Yr 425: Rehab 2 - Mill & Fill Age (yrs) 0 4 8 12 16 20 24 28 32 36 40 44 48 52 Asphalt Designs have Greater Risk on Rehabilitation Timing Proposed Rehabilitation Schedules for ALDOT LCCA Procedures: Asphalt based Auburn recommendation sand Concrete based on University of Alabama recommendations - 22 -
AGENDA Initial Performance Period Rehabilitation Performance Periods Rehabilitation Selection - 23 -
MOST LCCA GUIDELINES PROVIDE A SINGLE SET OF ACTIVITIES Rehab 1 Year 18 to 25 (Typical = Yr 22) Rehab 2 Year 28 to 32 (Typical = Yr 32) Diamond Grind 4-7% FDR 3 to 4 Asphalt Overlay 2% FDR = LCC Initial PCC Construction Question - is the selection of activities representative of the most likely set of activities for the pavement option? PCC Rehab Schedule, Ohio DOT LCCA Manual - 24 -
THE FACT IS THAT THERE ARE MANY POSSIBLE ACTIVITIES Some agencies provide a series of activities, but still use a standard in their LCCA Rehab 1 Year 18 to 25 (Typical = Yr 22) Rehab 2 Year 28 to 32 (Typical = Yr 32) 1% FDR Option 7 Initial PCC Construction Diamond Grind 3 to 6 AC Overlay 2-4% FDR 4-7% FDR 7-10% FDR 2-4% FDR 4-7% FDR 7-10% FDR Diamond Grind 3 to 4 Asphalt Overlay 125 2 ACOL No Mil Mil 2% FDR 3% FDR 1% FDR 2% FDR 3% FDR Option 8 Option 9 Option 10 Option 11 Option 12 Option 36 Increasing Life Cycle Costs A Robust LCCA will evaluate the Cost Impacts of all Alternate Rehabilitation Options PCC Rehab Schedule, Ohio DOT LCCA Manual - 25 -
USE PROBABILITY AND DECISION TREE ANALYSIS TO DETERMINE THE MOST LIKELY LIFE CYCLE COSTS Rehab 1 Year 18 to 25 (Typical = Yr 22) Rehab 2 Year 28 to 32 (Typical = Yr 32) Expected Value (EV n = Prob n x NPV n ) Initial PCC Construction Diamond Grind 90% 10% 3 to 6 AC Overlay 25% 50% 25% 2-4% FDR 4-7% FDR 7-10% FDR 2-4% FDR 4-7% FDR 7-10% FDR 50% 50% Diamond Grind 3 to 4 Asphalt Overlay 125 2 ACOL 25% 50% 25% No Mil Mil 1% FDR 2% FDR 3% FDR 1% FDR 2% FDR 3% FDR EV 1 = EV11= (09x05x05x05) x(npv11) EV11= Probability x NPV11 = (09 x 05 x 05 x 05) x ($25,950,132) = $2,919,390 NPV = Σ EV PCC Rehab Schedule, Ohio DOT LCCA Manual - 26 -
USE PROBABILITY AND DECISION TREE ANALYSIS TO DETERMINE THE MOST LIKELY LIFE CYCLE COSTS Rehab 1 Year 18 to 25 (Typical = Yr 22) Rehab 2 Year 28 to 32 (Typical = Yr 32) Expected Value (EV n = Prob n x NPV n ) Initial PCC Construction Diamond Grind 90% 10% 3 to 6 AC Overlay 25% 50% 25% 2-4% FDR 4-7% FDR 7-10% FDR 2-4% FDR 4-7% FDR 7-10% FDR 50% 50% Diamond Grind 3 to 4 Asphalt Overlay 125 2 ACOL 25% 50% 25% No Mil Mil 1% FDR 2% FDR 3% FDR 1% FDR 2% FDR 3% FDR EV1 = $675,27193 EV2 = $1,358,09610 EV3 = $682,82417 EV4 = $715,92176 EV5 = $1,439,39576 EV6 = $723,47400 EV7 = $1,370,84301 EV8 = $2,756,79050 EV9 = $1,385,94749 EV10 = $1,452,14267 EV11 = $2,919,38981 EV12 = $1,467,24714 EV13 = $695,57108 EV14 = $1,398,69440 EV15 = $703,12332 EV16 = $736,22091 EV17 = $1,479,99405 EV18 = $743,77314 EV19 = $193,60752 EV20 = $194,03381 EV21 = $195,03977 EV22 = $21,34290 EV23 = $21,39077 EV24 = $21,50254 EV25 = $346,28288 EV26 = $347,03448 EV27 = $348,82285 EV28 = $85,89453 EV29 = $86,08446 EV30 = $86,53155 EV31 = $152,41390 EV32 = $152,73998 EV33 = $153,52239 EV34 = $64,81310 EV35 = $64,95437 EV36 = $65,28969 EV11= Probability x NPV11 = (09 x 05 x 05 x 05) x ($25,950,132) = $2,919,390 NPV = Σ EV = $25,306,023 PCC Rehab Schedule, Ohio DOT LCCA Manual - 27 -
SAME ISSUES AND PROCESSES ARE ALSO HOLD FOR ASPHALT Initial AC Construction 90% 10% Rehab 1 Year 10 to 15 (Typical = Yr 12) 125 2 AC Overlay 2 to 3 AC Overlay 10% 90% No Mill Mill No Mill Mill Rehab 2 Year 18 to 25 (Typical = Yr 22) 50% 25% 25% 3-4 Mill/ACOL 4-6 Mill/ACOL 6-7 Mill/ACOL Rehab 3 Year 28 to 34 (Typical = Yr 34) 25% 25% 50% Crack Seal Microsurfacing Mill / 15 ACOL Expected Value (EV n = Prob n x NPV n ) EV1 = $195,13340 EV2 = $196,73250 EV3 = $399,86139 EV4 = $102,51867 EV5 = $103,31822 EV6 = $209,83463 EV7 = $107,47064 EV8 = $108,27019 EV9 = $219,73858 EV10 = $1,775,39715 EV11 = $1,789,78904 EV12 = $3,637,14562 EV13 = $932,26631 EV14 = $939,46225 EV15 = $1,907,70828 EV16 = $976,83405 EV17 = $984,02999 EV18 = $1,996,84375 EV19 = $90,14782 EV20 = $90,83314 EV21 = $184,40760 EV22 = $47,19618 EV23 = $47,53885 EV24 = $96,44835 EV25 = $49,31845 EV26 = $49,66112 EV27 = $100,69289 EV28 = $819,55745 EV29 = $825,72540 EV30 = $1,676,12261 EV31 = $428,87918 EV32 = $431,96316 EV33 = $876,26222 EV34 = $447,97964 EV35 = $451,06362 EV36 = $914,46314 EV12= Probability x NPV12 = (09 x 09 x 05 x 05 x 05) x ($23,092,988) = $3,637,146 NPV = Σ EV = $24,210,615 AC Rehab Schedule, Ohio DOT LCCA Manual - 28 -
HOW PROBABILITY AND DECISION TREE ANALYSIS CAN MAKE LCCA RESULTS MORE ROBUST AND TRANSPARENT Asphalt Design 16 Total Asphalt Concrete (15 Surf Typ A 125mm 15 Interm Typ A 19mm 13 AC Base) Concrete Design 145 PCC 15-ft Joints w/ 15 Dia Dowels $27095 6 Aggregate $23051 Base $23 6 Aggregate Base Δ = 105% Millions $28 $27 $26 $25 $24 $22 $22301 LCCA Results $26445 $24010 $25478 xxx = NPV from Standard LCCA xxx = NPV range from Decision Tree Analysis Subgrade Subgrade $21 $20 $19 $18 Asphalt Concrete Range of results addresses Risk Assumptions inherent in a standard LCCA Ohio DOT HAM-75-1010 (PID 76256) Pavement Type Selection (March 2007) - 29 -
HOW PROBABILITY AND DECISION TREE ANALYSIS CAN MAKE LCCA RESULTS MORE ROBUST AND TRANSPARENT Asphalt Design 16 Total Asphalt Concrete (15 Surf Typ A 125mm 15 Interm Typ A 19mm 13 AC Base) Concrete Design 145 PCC 15-ft Joints w/ 15 Dia Dowels Millions $28 $27 $26 $25 $24 $22 $27095 $22301 Δ = 45% $26445 $24010 $25478 $24211 $25306 6 Aggregate $23051 Base $23 6 Aggregate Base Δ = 105% LCCA Results xxx = NPV from Standard LCCA xxx = NPV range from Decision Tree Analysis = Expected Value from Decision Tree Analysis Subgrade Subgrade $21 $20 $19 $18 Asphalt Concrete Range of results addresses Risk Assumptions inherent in a standard LCCA Ohio DOT HAM-75-1010 (PID 76256) Pavement Type Selection (March 2007) - 30 -
CONCLUSIONS LCCA needs to be reasonable and reflect the likely agency expenditures and performance of the specific pavement design being evaluated 1 - Most agencies apply a single, standard, policy set rehabilitation scenario to all pavements Assumes that the historical performance used in the analysis will be representative of the performance of the specific design being evaluated This is probably not true 2 - Pavement-ME can improve the performance estimates / rehabilitation timing of different pavement designs Accounts for different Design Features on performance Can be used to account for increasing traffic and damage for rehabilitation activities - Decision Tree Analysis looks at all potential rehabilitation options and develops a range of Net Present Values (NPV) so that the associated Risk Profile of each alterative is defined 3 A Robust LCCA addresses the inherent uncertainty in LCCA s to balance the risk assumptions to make them more transparent, credible, and defensible - 31 -