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

2 ARA Proprietary

© 2011 Applied Research Associates, Inc.

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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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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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

Trucks Associated With Wind Farms (Turbine Components)

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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

Tomkins County10 Year Capital Plan

Big-picture, long-term assessment useful

Budgeting & capital planning

Basis for development impact fee

Gas Well Impact Fee Basis of Fee

Bradford County

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Global Impact Determination

Cost impact = (% pavement life consumed) X (pavement replacement cost)

% pavement life = projected trucks (ESALs)

pavement life (ESALs) consumed

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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

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

Truck Miles Projection (10 Years)

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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.

Need to Account For Variation in Loads

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Any load can be converted to 18,000 lb ESALs

Use Load Equivalency Factor

Relationship between axle weight & inflicted pavement damage is not linear but exponential

Individual Loads Converted to Standard ESAL

4

000,18

lbs

AxleWeightLEF

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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

ESAL Examples For Specific Axle Types & Weights

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Most trucks contain a combination of axle types & loads

ESALs for entire truck = sum of ESALs for each axle

ESALs Determined for Specific Trucks

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Water Truck (Triaxle)

• 2.5 ESALs

• 4.5 ESALs if 3rd Lift Axle is Up

Water Truck (Tractor Trailer)

• 1.00 ESALs

Examples of ESALs For Common Trucks

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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

ai = Layer coefficient of layer i

D i = Thickness of layer i

mi = Drainage coefficient of layer i

AC

Surface AC

Subbase

Base

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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

0.44

0.40

Granular subbase 0.11

Asphaltic concrete base course

Asphaltic concrete binder course

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Example SN Calculation for Existing Pavement

SN = 1.5”x 0.44 + 2.5”x 0.44 + 6” x 0.11

HMA

Surface Subbase

SN = 0.66 + 1.1 + 0.66

SN = 2.42

HMA

Binder

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SECTION A (THIN)

SECTION C (THICK)

AC

4” 2”

6”

6”

6” 6”

SUBBASE SUBGRADE

(FINE GRAINED)

Example Sections

SN= 1.54

(14,000 ESALs) SN= 2.42

(215,000 ESALs) SN= 3.30

(1,600,000 ESALs)

SECTION

B (Medium)

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Global Impact Determination

Cost impact = (% pavement life consumed) X (pavement replacement cost)

% pavement life =

consumed

projected traffic (ESAL-miles)

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 =

consumed

50 miles of pavement life fully consumed

50 mi X $2M/mi = $100 M

100,000,000 ESAL-mi

200,000ESALs (life)

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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

Expanding the Realm of Possibility

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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

Subgrade Soil

Base/Subbase

Surface SUR

SUB

d SUR

Axle Load

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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)?

Time (Years)

Pavement Condition

Good

Poor

$1 to rehab

$4-10 to rehab

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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???

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

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