ASTM E2176-08

The coefficient of retroreflected luminance, R_L, is the property of a pavement marking system that provides a measure of the retroreflective efficiency of the marking and depends on factors such as the materials used, age, and wear pattern. These conditions shall be observed and noted by the user.

Under identical conditions of headlight illumination and driver's viewing, larger values of R_L correspond to higher levels of visibility at corresponding geometry.

The pavement marking's measured retroreflective efficiency in conditions of continuous wetting may be used to characterize the properties of the marking on the road as water is continuously falling on it. The retroreflective efficiency of the marking in conditions of continuous wetting may be different than in dry, wet or damp conditions.

This test method may produce measurements of R_L-Rain for pavement marking systems that do not correlate to nighttime visibility distance during typical rain events. The rainfall intensity simulated by this test method is significantly greater than most ordinary or even heavy rainfall events. As a result, the test specimen, unless it has vertical features exceeding
3 mm, becomes flooded. Optics with an index of refraction less than 2.0 are practically ineffective when immersed in water. Thus, the test method is of limited applicability for assessing the wet retroreflective properties of pavement marking systems having vertical features less than 3 mm or optics having an index of refraction less than 2.0.

Retroreflectivity of pavement (road) markings degrades with traffic wear and requires periodic measurement to ensure that sufficient line visibility is provided to drivers.

Newly installed pavement markings may have a natural surface tension or release agents which prevent wetting of the marking by rain/water. This phenomenon produces unreliable and unrepeatable results when measuring retroreflective efficiency under wet conditions. This non-wetting phenomenon is generally eliminated after one month of wear and weathering on the road. A wetting agent can be used to estimate the R_L-Rain properties of new markings (see 5.4).

Roadway characteristics such as longitudinal slope, cross slope and pavement porosity will impact the results of this test method.

1.1 This test method covers a measurement of the wet retroreflective (R_L-Rain) properties of horizontal pavement marking materials, such as traffic stripes and road surface symbols.

1.2 This method of measuring wet retroreflective properties (R_L) of pavement markings utilizes a method of continuously wetting the marking during measurement (see Fig. 1).

Note 1—Test Method E 2177 may be used to describe the retroreflective properties of pavement markings in conditions of wetness after a period of rain.

1.3 This test method is most suitable for laboratory use under controlled conditions, but may also be used for field measurements when the necessary controls and precautions are followed.

1.4 This test method specifies the use of reflectometers that can measure pavement markings per Test Method E 1710. The entrance and observation angles required of the retroreflectometer in this test method are commonly referred to as “30 meter geometry.”

1.5 This test method has been shown to produce reasonable results for pavement marking systems with optics having an index of refraction greater than 2.0 and structured markings having vertical structures greater than or equal to 3 mm. Users should exercise caution when using this test method for pavement marking systems with optics having an index of refraction less than 2.0 or markings having vertical structures less than 3 mm.

1.6 Results obtained using this test method should not be the sole basis for specifying and assessing the wet retroreflective effectiveness of pavement marking systems. Users should complement the results of this test method with other evaluation results, such as nighttime visual inspections.

1.7 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

Note 2—An alternative test method designed to better represent the retroreflective efficiency of pavement marking systems under typical rain events is under development.

FIG. 1 Illustration of Measurement