U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
202-366-4000
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Conducting field surveys of the condition of pavement marking is not easy. Many aspects need to be considered prior to conducting field surveys. For example, markings are considered new within 14 days of installation, with all excess glass beads removed. When or how long after installation should retroreflectivity tests be taken? The fact is that it depends on the type of marking. Some markings can be read immediately after installation, and some should be allowed to brighten before their retroreflectivity is determined. Performance contracts for pavement markings are showing up throughout the United States across the country. And many of these contracts specify when readings will be taken.
Other items that should be considered prior to field inspection:
There are many factors (e.g., road surface, safety needs, alignment, material type) to be considered before pavement markings are installed. There is no one part or link in a pavement marking value chain that is more important then any other. One of the underlying premises of PMMS is that field inspections, or more specifically, the retroreflectivity of pavement markings, must be collected.
The following is included for consideration purposes only, and is not intended to take the place of any specific agency or organization specifications. It is provided as information to those agencies that have not performed field inspections. Agencies may also want to consider the following standards
ASTM Standards
Other Standards
The following specifies a procedure that can be used to evaluate the retroreflective performance of horizontally applied (in-service) pavement markings. This test procedure is only intended for field measurement. Because the entrance and observation angles of the retroreflectometer affect the readings of pavement markings the entrance and observation angles (geometry) shall be specified. Evaluation of pavement markings shall be done within specified zones and time intervals. Criteria are included for determining inspection zones that appear, by visual or mobile instrument inspection, to fall below the specified minimum performance value.
Retroreflective field data can be collected with either portable (i.e., handheld) or mobile reflectometers. The Engineer has the option of determining whether the readings shall be done at night or during daylight, but in either case the readings will be done in dry conditions. Data shall be collected in the direction of traffic, when ambient temperature conditions are compatible with specifications for the instrument. When encountering pavement markings that separate opposing traffic (i.e., centerline, lane line, skip lines, etc.), the Engineer may request that pavement markings be evaluated in both directions, and that the centerline be measured for each stripe.
This process is an improvement over visual inspections because it allows collection of data that can be used to objectively determine the retroreflective qualities of the installation. We do not intend to discourage visual inspections, especially visual inspections done at night. Visual nighttime inspections are encouraged because they may reveal deficient areas that should be inspected.
Instrument geometry is specified because it is a primary driver in determining retroreflective values. Thirty meters has been selected because it most closely correlates an average automobile drivers vision geometry. Instruments used to measure the retroreflective properties of pavement markings shall conform to the following measurement geometry(s):
All readings taken, or the coefficient of retroreflected luminance, shall be expressed as the metric equivalent (mcd/m²/lux).
Field evaluations (data collection) should not be started until the markings have been inservice for a minimum of 2 weeks. The 2-week minimum time frame is very dependent on the type of material that is being installed. Data collection should be completed within 6 weeks of installation (weather permitting). Waiting any longer could jeopardize the ability of some marking material to meet minimum values. This is especially true for areas with high volumes of traffic or areas where vehicles make numerous turning movements.
After field evaluations are completed, a written report shall be submitted to the Engineer Contained within the report shall be:
The evaluation of longitudinal pavement markings shall be made after identifying the zone(s) to be measured. Any installation less than 300 meters (1000 feet) shall be considered a zone. One zone of measurement should be identified for installations that fall between 300 meters and 1.5 kilometers. Any installation greater than 1.5 kilometer shall have a minimum of one zone selected for each kilometer of striping. The 300 meters shall be continuous in length. The random segment(s) may be selected after a visual inspection. A minimum of 26 readings on each line will be taken within each test zone. When reading broken lines (skip stripes), every other skip shall be read, with no more then three readings taken on any one skip stripe. A minimum of two readings should be taken on individual skip lines, and they should be taken approximately 500 millimeters (20 inches) from each end of the skip. On continuous lines, break the measurement zone into a minimum of ten 30-meter (IOO-foot) areas, and space the 25 readings a minimum of 33 feet apart but no more than 100 feet apart. The Engineer may determine that more samples shall be taken.
Note: After the initial evaluation, regardless of the results, the-Engineer can define new checkpoint areas if they are considered critical for road safety.
Mobile instruments shall conform to specified geometry and shall be capable of reporting both mcd/m²/lux average and standard deviation for each line and each segment. When reading longitudinal lines, the minimum interval for averaging both, a segment’s individual mcd/m²/lux readings and the segment’s standard deviation will be no less than 100 feet; however, all of the individual readings shall be used when determining a zone’s overall average. Inspectors shall not group together, in any one report, two lines or two color lines in the same data file. When collecting data on longitudinal continuous lines, readings shall be collected at a minimum rate of not more than 8 feet apart. When collecting data on longitudinal broken lines, readings shall be collected at a minimum rate of not more than 5 feet apart.
Repeatability of the mobile instrument shall be considered acceptable if the instruments deviation within the same inspection zone is +10%. The maximum acceptable deviation for measurements made by two different instruments manufactured by the same manufacturer, within the same zone of measurement, shall not be greater than +15%. The calibration of the instrument shall conform to the manufacturers instructions. Mobile instruments shall measure a minimum of 20% of each installed line. And, reading entire segments of installed lines should be considered.
Note: Upon evaluation, despite the results of the inspection, the Engineer can define additional inspection areas if they are considered, critical for road safety.
Symbols and Legends
For each contract, the zone of measurement can be considered as the contract length. Inspectors shall take and report a representative sample of each type of symbol.
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