Method for Testing the Retroreflectivity Luminance (RL) Coefficient of Road Markings under Standard Humid Conditions

The nighttime performance of road markings is determined by the coefficient of Retroreflectivity Luminance, RL， be it dry or wet, and depends on the materials used, age, and wear pattern. These conditions shall be observed and noted by the user. Under the same conditions of headlight reflectivity and driver’s viewing, larger values of RL correspond to higher levels of visual performance at corresponding geometry. The retroreflectivity, RL of road markings degrades with traffic wear and requires periodic measurement to ensure that sufficient visibility is provided to drivers.

Both a dry and a wet measurement are usually taken in order to characterize the performance of the marking. The dry measurement establishes the effectiveness of the marking in a dry condition plus provides a bench mark for the marking to which the wet performance can be compared. However, the dry measurement is optional per this test method.

1.Measuring Dry or Wet Retroreflectivity (RL) of Markings：

A. Use the manufacturer's instructions for calibration and operation of the retroreflectometer.

B. Locale the area of the pavement marking to be measured.

C．Place the retroreflectometer squarely on or behind the measurement area with the reflectivity in the direction of travel. Ensure that the illuminated measurement area of the retroreflectometer within the width of the stripe, and take a measurement.

2. Measuring Retroreflectivity (RL) in a Standard Condition of Wetness:

A.    Pour 3.0 liters of clean water from a bucket over the measurement area within 3 to 5 s and begin timing when the bucket is emptied. The water is poured evenly along the test surface so that the measuring field and its surrounding area is momentarily flooded by a crest of water (see Fig.1).

B. Measure the coefficient of retroreflected luminance, of the wetted marking 45 s after pouring water on the marking as described in 2.A (see Fig. 1).

C．Records—Record the dry and wet measurements in mill candela per square meter per lux, (mcd/m2/lx). Move to next measurement location which is separated sufficiently to provide mill candela and repeat procedures in 2.A and 2.B.

Factors That May Influence Measurements

There are several factors that may cause measurement variability when taking readings in the field. Some of these are: Slight changes in the position of the reflect meter on or in front of the traffic line may yield different readings. The magnitude of the wet measurement obtained may sometimes be dependent upon how well the water drains "off from" the markings. Steep inclines will allow the water to run off quickly and lead to higher values. Conversely, low areas or dips will allow the water to puddle and will give lower values. Environmental conditions that can effect evaporation ale are such as road temperature, air temperature, wind velocity, relative humidity, sun exposure and altitude.

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