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Impacts of energy development on low volume roads paul wilke, pe
- 1. IMPACTS OF ENERGY
DEVELOPMENTS ON LOW
VOLUME ROADS
Paul W. Wilke, P.E.
Principal Engineer
- 2. Presentation Outline
Background - Wind & Gas Development
Policy Considerations for Road Owners
Global Impact vs Site Specific User Fee Approaches
Technical Procedure for Each Approach
Comparison of Approaches
Special Considerations:
Technical
Administrative
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© 2011 Applied Research Associates, Inc.
- 3. Introduction
Energy development boom across USA and
Canada
NY has wind & PA has gas…
NY- many wind farms developed; gas coming soon?
PA- natural gas development boom since 2008
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© 2011 Applied Research Associates, Inc.
- 5. How Large Are The Loads?
Wind Farms:
Large volume of “legal loads” (<80,000 lbs)
Smaller number of “super loads”
Gas Wells:
Large volume of “legal loads”
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© 2011 Applied Research Associates, Inc.
- 6. Trucks Associated With Wind Farms
(Turbine Components)
Huge Blades
• 3 blades/turbine
• Typical length: 115-165 ft
• Typical weight: 5-10 tons
Huge Tower
• 3 or 4 pieces
• Typical height: 210-280 ft; can be
as high as 330 ft
• Each segment weighs 50-75 tons
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- 7. Turbine Components (cont’d)
Nacelle
• 1 or 2 pieces
• weight ~65-125 tons
Base Concrete
• 430 CY per turbine
(43 truck loads)
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- 8. Turbine Cranes
Main Cranes
• Initial construction requires 35 trucks
• Reconstruction requires 10 trucks
• Reconstructed 5 times per 50 turbines
(may vary with turbine layout)
Support Cranes
• 5 support cranes required for
construction of each main crane
• Each support crane requires 5 trucks
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- 9. Other Sources of Loads
Hauling Materials for Access Road
Construction
• Typical section : 16ft wide, 12-in thickness
• Requires 313 10-CY trucks/mile of access road
• 1 truckload of H2O per 105 CY aggregate on
access roads
• Access roads sprayed 1-3 times/day for dust
control
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- 10. Wind Farm Trucking
Large number of “legal loads” & some “superloads”
Sxxxesals
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- 11. Trucks Associated with Gas Wells
Hydraulic Fracturing Process Requires Trucks For:
• Water
• Sand & other chemicals
• Other construction materials
Typically 1300 trucks/well site
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- 12. Pennsylvania “Gas Rush”
Drill Baby Drill….
1000’s of wells developed last 4 years
Anticipate 20 years development
4,500 miles of roads affected
PennDOT has jurisdiction over most roads
(including “county roads”)
Opportunity for NY to learn from PA
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- 13. Posted Roads in One PA County
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- 15. Weak Roads
Many energy sites accessed by low volume roads
(County & Town owned)
Pavements not designed for heavy truck traffic
Substantial failures have
occurred
Many roads warranted
structural upgrade
before hauling
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- 16. How Should Road Owners Respond
To This New Road Usage?
Anticipate development & improve roads in advance
Encourages development (should taxpayers pay?)
Seek reimbursement from industry for road damage
Policies should be developed- address these
& many related issues
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© 2011 Applied Research Associates, Inc.
- 17. Seeking Reimbursement From Developers
(Two Fundamental Approaches)
Global impact recouped
through development
impact fee
Road & company specific
user fee
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- 18. Global Impact Fee Approach
• Up-front effort to develop fair assessment
• Could include other impacts (bridges,
environment)
• Less administrative effort once in place
• Some inequalities
E.g. -County A collects impact fee
- County A & B roads used
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- 19. User Fee Approach
• More direct (project specific) allocation of costs
• Ongoing effort required to administer
• Some (or all) of administration cost could be borne
by developer
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- 20. Methods Developed for PennDOT
PennDOT using a hybrid approach
User fee charged on “posted roads”
Roads where significant traffic expected-posted for 10 Tons
Hauler posts bond & enters an “excess maintenance”
agreement
Impact fee to compensate for “non-posted” roads
ARA study to estimate global impact to non-posted roads
State levied an impact fee to compensate for road & other
impacts
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- 21. General Concepts
Impact is based on “pavement life” consumed
Global impact & user fee methods similar
Global impact
• network level assessment of “projected” damage
• assumed average pavement structure
User fee
• project level assessment
• based on “actual” trucks, pavements & damage
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- 22. Estimate of Global Impact
Big-picture, long-term assessment
useful
Budgeting & capital planning
Basis for development impact fee
Bradford County Gas Well Impact Fee
Tomkins County Basis of Fee
10 Year Capital Plan
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- 23. Global Impact Determination
Cost impact = (% pavement life consumed) X
(pavement replacement cost)
projected trucks (ESALs)
% pavement life =
consumed pavement life (ESALs)
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- 24. Projected Truck Trips
1st- project the extent of development
2nd- estimate truck loading related to development
PennDOT example:
• Number of wells projected from industry estimates (1,300
trucks/well)
• Average trip = 10 miles
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- 25. Project Truck-Miles Associated
with Expected Wells
Truck Miles Projection (10 Years)
County # of Wells # of Trucks Avg Trip Truck-Miles
Projected per Well Length (mi) Projected
County A 1,210 1,300 10 15,730,000
County B 855 1,300 10 11,115,000
County C 2,100 1,300 10 27,300,000
County D 970 1,300 10 12,610,000
Totals 66,755,000
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- 26. Need to Account For Variation in Loads
AASHTO developed a method to convert various
truck axle configurations & weights to one standard
Standard = Equivalent Single Axle Load (ESAL )
One ESAL is equivalent to an 18,000 lb.
weight on a single axle with dual tires.
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- 27. Individual Loads Converted to Standard
ESAL
Any load can be converted to 18,000 lb ESALs
Use Load Equivalency Factor
4
AxleWeight
LEF
18,000lbs
Relationship between axle weight & inflicted
pavement damage is not linear but exponential
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- 28. ESAL Examples
For Specific Axle Types & Weights
Single axle (18,000 lbs)= 1.0 ESALs
Single axle (12,000 lbs)= 0.19
ESALs
Tandem axle (24,000 lbs)= 0.26 ESALs
Tandem axle (34,000 lbs)= 1.09 ESALs
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- 29. ESALs Determined for Specific Trucks
Most trucks contain a combination of axle types &
loads
ESALs for entire truck = sum of ESALs for each axle
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- 30. Examples of ESALs For Common Trucks
Water Truck (Triaxle)
• 2.5 ESALs
• 4.5 ESALs if 3rd Lift Axle is Up
Water Truck (Tractor Trailer)
• 1.00 ESALs
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- 31. Total ESALs Projected
Convert all truck types in fleet to ESALs
Determine total ESAL- miles for all projected
truck trips
Total ESAL- Miles
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- 32. ESAL Life of Representative Pavement
AASHTO design determines SN required to
support projected ESALs
Reverse process- ESAL life determined for
known SN
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- 35. Assess SN of Existing Roads
In Network
SN = a1 D1 + a2 D2 + a3 D3 m3
AC AC Subbase
Surface Base
ai = Layer coefficient of layer i
D i = Thickness of layer i
mi = Drainage coefficient of layer i
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- 36. Structural Layer Coefficient (ai)
Indication of a material's structural contribution to
pavement performance
Example:2 inches of material with ai = 0.20 provides
the same contribution as 1 inch of material with ai =
0.40
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- 37. Typical Layer Coefficients
Asphaltic concrete wearing course 0.44
Asphaltic concrete binder course 0.44
Asphaltic concrete base course 0.40
Granular subbase 0.11
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- 38. Example SN Calculation for Existing Pavement
HMA HMA Subbase
Surface Binder
SN = 1.5”x 0.44 + 2.5”x 0.44 + 6” x 0.11
SN = 0.66 + 1.1 + 0.66
SN = 2.42
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- 39. Example Sections
SECTION SECTION SECTION
A (THIN) B (Medium) 4” C (THICK)
2”
6”
6”
6”
6”
SN= 1.54
(14,000 ESALs) SN= 2.42
(215,000 ESALs) SN= 3.30
AC
(1,600,000 ESALs)
SUBGRADE
SUBBASE
(FINE GRAINED)
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- 40. Global Impact Determination
Cost impact = (% pavement life consumed) X
(pavement replacement cost)
projected traffic (ESAL-miles)
% pavement life =
consumed pavement life (ESALs)
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- 41. Example Calculation
100,000,000 ESAL-miles projected over road network
Typical County pavement life = 200,000 ESALS
% pavement life = 100,000,000 ESAL-mi
consumed
200,000ESALs (life)
50 miles of pavement life fully consumed
50 mi X $2M/mi = $100 M
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- 42. Two Alternative User Fee Approaches
Charge developer based on pavement life consumed
similar to global impact
uses project specific data
Charge developer for cost of repairing visible damage
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- 43. User Fee Based on Pavement Life Consumed
(Alternative Methods)
Mechanistic-Empirical Method
• Rigorous engineering procedure
• Costs more to perform
Empirical Method
• Simpler approach
• Less accurate
• Less cost to perform
Both Methods Based on SN-effective at start & end of
development
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- 44. Pre- & Post- Development Pavement Life
Determination
Mechanistic- Empirical Approach:
• FWD testing & pavement cores
• Back-calculation of elastic modulus
• Determine effective SN & remaining life
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- 45. Pre- & Post- Development Pavement Life
Determination
Empirical Approach:
• Pavement cores & surface condition survey
• Empirical correlations relate surface condition to equivalent
structural layer coefficients (a i*)
• SN effective = (a1*) + (a2*) + (a3*)
• Remaining life determined from SN effective (AASHTO design
equation)
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- 46. Visual Condition Survey
To Estimate SN effective
Alligator and L&T cracking % estimated
Reduced structural coefficient related to %
cracking
AASHTO Table 5.2 provides coefficient ranges
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- 48. Pavement Damage Assessment
(Based on Pavement Life Consumed)
SN effective used to quantify damage
Cost may be expresses as:
(% Pavement life lost) X ($ to rebuild pavement);
(% SN lost) X ($ to rebuild pavement)
$ for structural overlay to restore original SN
Same result, just different ways to express
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- 49. User Fee Method Based on Visible Damage Only
( “Patch & Go” Approach)
Some agencies only require repair of visible surface defects
Only condition survey required for assessment
Underestimates full extent of damage
Early fatigue cracking not considered
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- 50. Consider Flexible Pavement Behavior
& Fatigue Damage
Axle
Load
Surface SUR d SUR
Base/Subbase SUB
Subgrade Soil
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- 52. Early Stage of Fatigue Cracking
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- 55. Special Considerations:
Multiple Users of Permitted Roads
Allocate repair costs based on ESALs
Potential refinement for relative seasonal damage
Equivalent ESALs = ESAL X Seasonal adjustment factor
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- 56. Seasonal Adjustment Factor
Could derive factor for spring & winter
Spring thaw damage factor (SDF) =
Damage predicted during spring thaw
Damage predicted remainder of year
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© 2011 Applied Research Associates, Inc.
- 57. Seasonal Adjustment Factor
Spring Damage Factor (SDF) depends on:
• Asphalt layer stiffness & thickness
• Granular subbase stiffness & thickness
• Subgrade soil strength
Use mechanistic analysis (WINJULEA software) &
Asphalt Institute failure equation
SDF typically 2 to 4+ (higher for thin pavements)
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- 58. Other Issues To Consider
Assessment & allocation of road damage is
multi-faceted challenge
Analogous to “layers of an onion”:….
Consider the following:
Effect of pavement condition at start of permit period
Providing exemption for small haulers
Requirement to keep road safe for motoring public
Proactive maintenance/upgrade before winter
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- 59. Effect of Pavement Condition at Start of Permit
Is it fair to charge developer for rapid deterioration
near end of pavement life?
Is it fair for County to pay to rebuild a road not in CIP
(to accomodate permittee)?
Good $1 to rehab
Pavement
Condition $4-10 to rehab
Poor
Time (Years)
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- 60. Administrative Considerations
Post load restrictions & require Road Use Agreement
(RUA)
RUA provides mechanism for user fee
Performance bond to help enforce RUA
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- 61. Components of Road Use Agreement
Define methodology to assess road damage cost
allocation
Define procedure for pre & post- permit road inspections
Most RUA’s require developer to pay for inspections
Requirement for developer to maintain safe and
passable road
unsafe conditions corrected within 8 hrs
Winter maintenance plan submitted each fall
(avoid un-repairable condition)
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- 62. Components of Road Use Agreement (cont’d)
Developer responsible for repairs for 3 yrs
Provide exemption for small haulers
Establish threshold that triggers RUA
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- 63. Summary
Two fundamental approaches to road damage
assessment
Global impact recouped through development impact fee
Road & company specific user fee
Global impact may be estimated based on network
level assessment of pavement life consumed by
projected truck traffic
User fee methods:
Repair of visible damage that occurs during permit period
Pavement life consumed (similar to global approach using site
specific data)
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© 2011 Applied Research Associates, Inc.
- 64. Summary (cont’d)
Pavement life consumed may be determined by:
Empirical method (cores & visual assessment correlated to
effective SN)
Mechanistic-empirical method (FWD testing & mechanistic
analysis to calculate effective SN)
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© 2011 Applied Research Associates, Inc.
- 65. Summary (cont’d)
Issues to address in Road Use Agreement:
• Damage assessment methodology to be used
• Procedure to allocate damage costs when multiple users share
same road
• Could account for seasonal effects on damage per truckload
• Requirement to maintain road in safe & passable condition
• Exemption of small haulers
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- 66. Summary (cont’d)
Assessment of road damage is a multi-faceted challenge
Many agencies in process of developing policies
Need to balance:
• Fairness/technical accuracy with ease/cost of administration
• Encourage development while protecting taxpayer’s
infrastructure investment
No one solution that “fits all”
Policies best developed by:
• Technical experts that understand issues
• Administrators that can implement efficient policies
• Elected officials with appreciation of political ramifications
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© 2011 Applied Research Associates, Inc.
- 67. Learning Assessment
1. What are 2 “fundamental” ways counties can recoup
cost to compensate for road damage from heavy
haulers?
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- 68. Learning Assessment (cont’d)
2. The relative effect of different truck types on
pavement damage may be assessed by:
a. Gross weight of the truck
b. Number of axles on the truck
c. Number of equivalent single axle loads (ESALs) for the truck
d. All of the above
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- 69. Learning Assessment (cont’d)
3. The concept of “pavement life consumed” used in
damage assessment is based on:
a. the portion of paved surface worn off
b. the extent of rutting
c. the portion of ESALs applied compared to ESAL’s pavement is
designed to accommodate
d. none of the above
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- 70. Learning Assessment (cont’d)
4. What is a common technique used by highway
agencies to “draw-in” developers to execute a Road
Use Agreement ?
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- 71. Learning Assessment (cont’d)
5. The relationship between a truck’s axle weight &
damage inflicted on the pavement is:
a. Exponential
b. Linear
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- 72. Learning Assessment (cont’d)
6. What affect(s) will raising the “lift axle” on a triaxle
truck have:
a. Reduce tire wear, thereby saving the truck owner money
b. Increase pavement damage
c. Increase the ESALs for the total truck regardless of cargo weight
d. All of the above
e. None of the above
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- 73. Learning Assessment (cont’d)
7. The structural layer coefficient used in AASHTO
pavement design:
a. Increases with pavement age and loading
b. Decreases with pavement age and loading
c. Is usually unaffected by pavement age and loading
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- 74. Learning Assessment (cont’d)
8. The pavement life consumed may be estimated by
considering:
a. Visual distress correlated to pavement strength (Structural
Number)
b. Falling weight deflectometer testing
c. Design life of the pavement (expressed in ESALs)
d. All of the above
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- 75. Learning Assessment (cont’d)
9. Assessing road damage based on visible distress alone:
a. Is an unacceptable procedure
b. Is easier to administer than other more rigorous procedures
c. Is a good way to account for early stages of fatigue cracking
d. Is rarely used by road owners
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- 76. Learning Assessment (cont’d)
10. The extent of road damage per truck load is
influenced by:
a. The weight of the truck
b. The number of axles supporting the truck
c. The point in the service life of the pavement at the time of
load application
d. All of the above
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- 77. Questions???
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© 2011 Applied Research Associates, Inc.