Impacts of energy development on low volume roads paul wilke, pe

IMPACTS OF ENERGY
DEVELOPMENTS ON LOW
VOLUME ROADS

Paul W. Wilke, P.E.
Principal Engineer

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.

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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Effect on Transportation
 Large loads  Weak roads

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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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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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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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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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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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Wind Farm Trucking
 Large number of “legal loads” & some “superloads”

 Sxxxesals

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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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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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Posted Roads in One PA County

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Potential Marcellus Development in NY

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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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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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Seeking Reimbursement From Developers
(Two Fundamental Approaches)
Global impact recouped
through development
impact fee
Road & company specific
user fee

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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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AASHTO Design Nomograph

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DARwin Design Software

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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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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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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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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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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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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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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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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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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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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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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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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

ytilibissoP fo mlaeR eht gnidnapxE

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AASHTO Layer Coefficients

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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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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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Consider Flexible Pavement Behavior
& Fatigue Damage
Axle
Load

Surface  SUR d SUR

Base/Subbase  SUB
Subgrade Soil
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Propagation of Fatigue Cracking

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Early Stage of Fatigue Cracking

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Intermediate Stage of Fatigue Cracking

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Advanced Stage- Fatigue Cracking

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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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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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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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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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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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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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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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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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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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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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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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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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Learning Assessment
1. What are 2 “fundamental” ways counties can recoup
cost to compensate for road damage from heavy
haulers?

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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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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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4. What is a common technique used by highway
agencies to “draw-in” developers to execute a Road
Use Agreement ?

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5. The relationship between a truck’s axle weight &
damage inflicted on the pavement is:
a. Exponential
b. Linear

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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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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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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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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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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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Questions???

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Impacts of energy development on low volume roads paul wilke, pe

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