Minnesota Department Minnesota Department of Transportationof Transportation

Mn/DOT’s Gradual Shift Mn/DOT’s Gradual Shift from Profile Index to IRIfrom Profile Index to IRI

Chronology of Shift to IRIChronology of Shift to IRI

19991999::

• Participated in FHWA’s Lightweight Profiler Study, hosting various vendors at MnRoad site

• Overall, LWP devices involved in study demonstrated moderate repeatability and poor reproducibility

Chronology of Shift to IRIChronology of Shift to IRI

20012001::

• Purchased Ames Lightweight Profiler and ARRB Walking Profiler

• Began performing random Quality Assurance on projects with ride incentive determined from 0.2” blanking band Profile Index

Mn/DOT’s Lightweight Profiler

Chronology of Shift to IRIChronology of Shift to IRI

20022002::

• Initiated Profile Index Smoothness Measuring Device Program in spring

• During QA on job sites, experienced problems replicating contractors’ 0.2” blanking band Profile Index values

Empirical DataEmpirical Data::

• Projects with 0.2” blanking band PI value of 0.0 possessed IRI values ranging from roughly 27 - 42 in/mi

• Projects with 0.2” blanking band PI value of 1.0 possessed IRI values ranging from roughly 29 - 46 in/mi

0.2” Blanking Band PI vs. IRI0.2” Blanking Band PI vs. IRI

Chronology of Shift to IRIChronology of Shift to IRI

2002 - 20032002 - 2003::

• Analyzed extensive certification and construction data, finding a very weak correlation between 0.0” and 0.2” blanking band Profile Index results

Chronology of Shift to IRIChronology of Shift to IRI

20052005::

• Let 13 additional bituminous IRI pilot construction projects

20042004::

• Let three bituminous IRI pilot construction projects

Chronology of Shift to IRIChronology of Shift to IRI

20062006::

• Let three concrete IRI pilot projects (results pending)

• Switched to IRI exclusively on bituminous construction projects

• Began using Pathways High Speed Profiler for Quality Assurance purposes

Mn/DOT’s High Speed Profiler

Bituminous Ride Incentive EquationsBituminous Ride Incentive Equations

IRI (in/mi)Incentive

(per 0.1 mi)

< 30 $400

30 - 65 $[850 - (IRI * 15)]

> 65 -$900 or CA

IRI Equation A (Typically 3-lift construction)

IRI (in/mi)Incentive

(per 0.1 mi)

< 33 $270

33 - 75 $[600 - (IRI * 10)]

> 75 -$675 or CA

IRI Equation B (Typically 2-lift construction)

IRI (in/mi)Incentive

(per 0.1 mi)

< 36 $180

36 - 85 $[414 - (IRI * 6.5)]

> 85 -$450 or CA

(Typically 1-lift construction)

IRI Equation C

-$1,000

-$800

-$600

-$400

-$200

$0

$200

$400

$600

0 10 20 30 40 50 60 70 80 90 100

IRI (in/mi)

Ince

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r 52

8-Fo

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ent

Equation A ----- Equation B ----- Equation C -----

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28-F

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Bituminous Ride Incentive Equations

Bituminous IRI % Improvement TableBituminous IRI % Improvement Table

ImprovementIncentive

(per 0.1 mi)

75.0% or more $150

60.1% - 74.9% $100

50.0% - 60.0% $50

30.0% - 49.9% $0

20.0% - 29.9%* -$50

10.1% - 19.9%* -$100

10.0% or less* -$450 or CA

IRI % Improvement Table(Typically 1-lift construction with Initial IRI ≥ 120)

*No disincentive for segments with an Initial IRI < 60 in/mi and a non-negative % Improvement

• Incentive/disincentive calculated for each 528-foot segment

• Payment is based on right wheel path IRI values (9 feet from left stripe)

• IRI data collected by contractor with certified profiler

• Bump/dips established with profilograph

Ride Incentive InformationRide Incentive Information

20072007::

• Will use IRI exclusively to determine ride incentive for all construction projects

Chronology of Shift to IRIChronology of Shift to IRI

Any Questions?Any Questions?