Verification of Retroreflectivity
Transcript of Verification of Retroreflectivity
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Verification of Retroreflectivity
Adam Pike, P.E. Texas A&M Transportation Institute
2015 Transportation Short Course
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What Is Retroreflectivity? • Retroreflectivity is the efficiency of a material
to return light in the general direction from which it came
• Coefficient of Retroreflected Luminance (RL) is the most commonly used measurement of retroreflectance for pavement markings
• Units: mcd/m2/lux
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Data Collection Equipment: Retroreflectometers
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TxDOT Areas of Interest • Item 666 - Retroreflectorized Pavement Markings
• 4.4 – Retroreflectivity Requirements • 4.5 – Retroreflectivity Measurements
• 4.5.1 – Mobile Retroreflectometer Measurements • 4.5.2 – Portable Retroreflectometer Measurements
• January 28,2015 – Memorandum requiring all non-profile longitudinal pavement markings to meet retroreflectivity requirements
• TxDOT Special Specification – Mobile Retroreflectivity Data Collection for Pavement Markings
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TxDOT Special Specification: Mobile Retroreflectivity Data Collection for
Pavement Markings • Specification requires contractor certification at TTI • Specification describes the following requirements
• Data files • Data mapping • Video • Field spot checks • Retroreflectivity verification requirements
• Specification is currently being modified to incorporate retroreflectivity verification
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Certification Program Background • Certification program began in Spring 2007 • Program was developed after TxDOT questioned
the validity of mobile retroreflectivity data that was submitted as part of a contract
• The data was highly variable and didn’t always make sense
• TxDOT questioned the ability of the contractor to operate the equipment and wanted contractors to be tested to make sure they have the ability to collect accurate data
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Certification Program Overview • Prior to conducting work for TxDOT, contractors must
come to TTI and pass the certification test • Certification testing is required for all new operators • Closed course and open road testing • All line types and colors measured • Field verification checks (retroreflectivity verification)
are now required to maintain certification • Loss of certification due to poor retroreflectivity
verification results requires full recertification testing • Certification program guide details information about
the program
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Certification Test Area
• Paint, tape, thermoplastic, and epoxy markings • White and yellow, all marking patterns, RRPMs
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Certification Testing • Yellow lines measured from left side of vehicle • White lines measured from right side of vehicle • Mobile retroreflectivity data must be within
±15% of the handheld retroreflectivity value collected on the same pavement marking segments
• Data is evaluated for each individual run and for the test as a whole
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Year • Currently certified: 11 TX contractors, 3 from out of state • 3 different mobile measurement devices have been certified • Several other measurement devices in development
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Retroreflectivity Verification Testing • Federal regulations require DOTs to verify
contractor test results for performance based product acceptance
• Guideline is to perform verification on a minimum of 10% of projects
• TTI is working with TxDOT to meet these requirements • Verification or spot monitoring can also be conducted
by districts contracting the work to ensure accurate data is consistently collected
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Retroreflectivity Verification Testing
• TTI is using a SiteManager materials report to monitor and select projects
• Project selection is based on a stratified random sample
• Initially selecting 20% of projects with a goal of evaluating 15% to ensure the 10% requirement is met
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Retroreflectivity Verification Testing • Contractors mobile data will be compared to
mobile data collected by TTI (supplemented with handheld readings for accuracy verification)
• TTI verification data to be collected within 7 days of contractor data
• Contractors and/or TxDOT will be required to keep TTI informed of scheduled mobile retroreflectivity data collection activities
• The contractors will not know which projects TTI has selected for verification testing
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Data Analysis • TTI will be checking two things
1. Does the contractor data fall within ±15% of the TTI data (The acceptable difference between the two data sets may be modified as the verification testing proceeds)
2. Does the contractor and/or TTI data meet the retroreflectivity requirements
• An adequate sample size will be evaluated to account for variability of the measurements
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Notification of Results • TTI will provide the results to the TxDOT engineer in
charge of the project as well as the contractor • Possible results:
• Data verifies and is above requirements (good) • Data verifies but is below requirements (restripe) • Data verifies but is above/below requirements (referee test?) • Data does not verify but is above requirements (corrective actions) • Data does not verify and is below requirements (restripe,
corrective actions) • Data does not verify and is above/below requirements (referee
test?, corrective actions)
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Corrective Actions • Corrective actions need to take place or
certification status can be lost after multiple failed verification tests
• Recommended corrective actions will be provided to the contractor with the results
• Possible corrective actions • Have equipment serviced • Improve calibration procedure and frequency • Adjust software settings • Monitor data collection conditions
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Referee Testing • The Engineer can choose to use either the contractor
or the TTI data to determine if the marking meets the retroreflectivity requirements
• The Engineer can request referee testing if they are unsure of the data
• If the contractor has issue with the TTI results referee testing can be requested • Most likely to occur when the data does not validate and
the TTI data indicates the retroreflectivity requirements are not met whereas the contractor data indicates the requirements are met
• CST will perform the referee testing using handheld retroreflectometers
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Next Steps • Get final approval on revised special specification • Notify districts and contractors of the revised special
specification • Distribute revised certification program guide to
contractors • Implement full scale retroreflectivity verification
program • Assist districts and/or conduct retroreflectivity
training if there are questions about the retroreflectivity requirements
• Add new material to certification/verification website
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Contact Info: Adam Pike Associate Research Engineer TTI Signs and Markings Program [email protected] 979-862-4591 tti.tamu.edu/group/visibility/mobile-retro-certification
Questions?