Section 6: Retroreflectivity Performance Specifications for Contracts
Introduction
Final contract acceptance is a quality-assurance measure that
involves inspecting the markings a certain amount of time after
all markings have been placed to ensure long-term performance.
Retroreflectivity performance-based pavement marking contracts have
been used successfully in other states for years as a final acceptance
measure. Such contracts are attractive because they shift specifications
away from the traditional recipe process to an objective performance
process, placing greater responsibility on contractors and manufacturers.
In addition, retroreflectivity measurement provides a numeric comparison
of how efficiently a marking returns light to the driver’s eyes, thereby
reducing the subjectivity that exists when performing nighttime
visual evaluations.
Final acceptance for TxDOT pavement marking contracts is usually
based on whether the markings meet a specified minimum level of
retroreflective performance. Compliance is often determined by a
series of retroreflectivity measurements, which are taken a specified
number of days after placement of the markings to allow for removal
of loosely adhered glass beads. The purpose of using retroreflectivity
measurements for final acceptance is to provide a reasonable amount
of assurance that newly applied markings will meet or exceed service
life expectations.
Performance Factors
All retroreflective performance specifications include three
important factors:
- minimum retroreflectivity values
- timing of measurements
- number of measurements.
Basis for Specification Compliance
Upon collection of retroreflectivity data, compliance with the specification is usually based on both of the following:
- The retroreflectivity average for a given pavement marking section is greater than the specified minimum value.
- The percentage of measurements that are less than the specified minimum retroreflectivity value for a given pavement marking section is below the specified minimum percentage.
The final acceptance period and performance of the corresponding retroreflectivity measurements should be in accordance with TxDOT specifications. Test Method
should only be used as a guide in determining the nighttime brightness and appearance of the markings, not for final acceptance purposes.