Designation: E 2177 – 01

Standard Test Method for

Measuring the Coefficient of Retroreflected Luminance (RL)
of Pavement Markings in a Standard Condition of Wetness1
This standard is issued under the fixed designation E 2177; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.

1. Scope
1.1 This test method covers the measurement of the wet
retroreflective (RL) properties of horizontal pavement marking
materials, such as traffic stripes and road surface symbols,
using a portable or mobile retroreflectometer that can be placed FIG. 1 Illustration of Measurement
on or before the road marking to measure the retroreflection at
the prescribed geometry.
Newly Applied Pavement Marking Using Portable Hand-
1.2 This method of measuring the wet retroreflective prop-
Operated Instruments3
erties (RL) of pavement markings measures the wet retroreflec-
E 691 Practice for Conducting an Interlaboratory Study to
tivity in a standard condition of wetness (see Fig. 1).
Determine the Precision of a Test Method4
1.2.1 Discussion—This test condition typically exists (1)
E 965 Test Method for Measuring Pavement Macrotexture
after a rainfall has ended and the pavement markings are still
Depth Using a Volumetric Technique5
wet or (2) as the markings are wet from dew or humidity.
E 1710 Test Method for Measurement of Retroreflective
1.3 Retroreflective performance obtained with this test in
Pavement Marking Materials with CEN-Prescribed Geom-
conditions of wetness does not necessarily relate to how
etry Using a Portable Retroreflectometer5
markings perform in conditions of rain, that is, as markings are
E 2176 Test Method for Measuring the Coefficient of Ret-
being rained upon.
roreflected Luminance (RL) of Pavement Markings in a
NOTE 1—Test Method E 2176 defines a method to use to measure the Standard Condition of Continuous Wetting5
performance of pavement markings in conditions of simulated rain. 2.2 Other Standard:
1.4 This test method specifies the use of portable or mobile CEN–EN 1436 Road Marking Materials—Road Marking
reflectometers that can measure pavement markings in accor- Performance for Road Users6
dance with Test Method E 1710.2 The entrance and observation
angles required of the retroreflectometer in this test method are 3. Terminology
commonly referred to as “30 meter geometry.”2 3.1 coeffıcient of retroreflected luminance, RL—the ratio of
1.5 This standard does not purport to address all of the the luminance, L, of a projected surface to the normal illumi-
safety concerns, if any, associated with its use. It is the nance, E, at the surface on a plane normal to the incident light,
responsibility of the user of this standard to establish appro- expressed in candelas per square metre per lux [(cd·m-2)/lx].
priate safety and health practices and determine the applica- Because of the low luminance of pavement markings, the units
bility of regulatory limitations prior to use. commonly used are millicandelas per square metre per lux
[(mcd·m-2)/lx].
2. Referenced Documents 3.2 condition of wetness—the test condition is created by
2.1 ASTM Standards: liberally wetting the road marking and waiting a certain time
D 6359 Specification for Minimum Retroreflectance of period after wetting for water to run off.
3.2.1 Discussion—Similar conditions exist when road
markings are wet or damp such as typically found after a rain
1
This test method is under the jurisdiction of ASTM Committee E12 on Color has ended or from dew and high humidity.
and Appearance and is the direct responsibility of Subcommittee E12.10 on
Retroreflection.
3.3 mobile retroreflectometer—a retroreflectometer that has
Current edition approved Dec. 10, 2001. Published February 2002.
2
Reference ASTM E 1710 “Standard Test Method for Measurement of Retrore-
3
flective Pavement Markings with CEN-Prescribed Geometry Using a Portable Annual Book of ASTM Standards, Vol 04.03.
4
Retroreflectometer.” The standard measurement condition is intended to represent Annual Book of ASTM Standards, Vol 14.02.
5
the angles corresponding to a distance of 30 m for the driver of a passenger car with Annual Book of ASTM Standards, Vol 06.01.
6
an eye height of 1.2 m and a headlight height of 0.65 m above the road. See Available from European Committee for Standardization, Central Secretarial
Appendix X1. (CEN), rue de Stassart 36, B1050, Brussels, Belgium.

Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.

1
 E 2177
been mounted to a vehicle for purposes of taking measure- 30 m, an eye height of 1.2 m and a headlight mounting height
ments while the vehicle is moving. of 0.65 m (see Appendix X1).
3.4 portable retroreflectometer—an instrument that can be 4.8 It shall be the responsibility of the user to employ an
used in the field or laboratory for measuring the coefficient of instrument having the specified observation and entrance
retroreflected luminance, RL. angles.
3.5 “recovery method” or “bucket method”—alternative
names commonly used to describe this test method for achiev- 5. Apparatus
ing measurements in condition of wetness. 5.1 Portable or Mobile Retroreflectometer—The reflecto-
3.6 RL-wet—the retroreflectance value, RL, obtained 45 s meter must comply with Test Method E 1710.
after wetting. (See Fig. 2.) 5.2 Stopwatch or Watch, with second hand.
5.3 Water, for wetting the pavement marking.
5.3.1 A portable hand sprayer (garden sprayer) may be used
to wet the pavement marking to create the wet condition. The
portable hand sprayer shall have an adjustable nozzle. A battery
operated unit works well.
5.3.2 Alternatively a bucket may be used to create the wet
condition by pouring the water over the marking. Approxi-
mately 2 to 5 L of water are needed.
5.3.3 The water shall be clean tap water.
6. Sampling
6.1 The number of readings to be taken at each test location
and the spacing between test locations shall be specified by the
FIG. 2 Definition of RL-Wet user.
6.2 It is common to take less frequent measurements than
4. Significance and Use one would do when assessing dry retroreflectance.
4.1 The nighttime performance of pavement markings is 6.3 Measurements for each line type shall be averaged for a
determined by the coefficient of retroreflected luminance, RL, final result.
be it dry or wet, and depends on the materials used, age, and
wear pattern. These conditions shall be observed and noted by 7. Calibration and Precautions
the user. 7.1 The portable or mobile retroreflectometer shall be cali-
4.2 Under the same conditions of headlight illumination and brated (standardized) using the instructions from the instru-
driver’s viewing, larger values of RL correspond to higher ment manufacturer. A reference or working standard is used
levels of visual performance at corresponding geometry. and is supplied with the instrument.
4.3 The pavement marking’s measured performance in the 7.2 Transporting the portable reflectometer from an air
standard condition of wetness is used to characterize the conditioned area to the test site may result in fogging of mirrors
performance of the marking on the road when wet. in the instrument. If there is any doubt concerning the
4.4 Newly installed pavement markings may have a natural calibration or if the readings of a reference or working standard
surface tension or release agents that prevent wetting of the are not constant, allow the instrument to reach ambient
product by water. The water will tend to “bead up” on the conditions and recalibrate with the reference or working
marking. This “non wetting” condition is usually short lived. standard.
Pavement markings that have been on the road for one month 7.3 Verification must be made that there is no moisture on
prior to testing usually do not exhibit this non-wetting phe- the instrument’s lens when the instrument is being used for wet
nomenon. (Warning–This phenomenon produces an interfer- readings. Sometimes the reflectometer’s lens will become
ence when assessing the wet characteristics of a pavement “fogged over” in high temperatures due to water evaporation.
marking. Attempts to measure markings with this surface When roads are hot one can pre-cool the road with water before
“non-wetting” or “beading” of the water may give higher applying the test method to prevent the reflectometer from
values.) fogging.
4.5 The retroreflectivity, RL, of pavement (road) markings 7.4 Calibration Recheck—If the subsequent readings on the
degrades with traffic wear and requires periodic measurement reference standard deviate by more than 5 % from the initial
to ensure that sufficient line visibility is provided to drivers. one, re-calibration shall be performed. If the readings on the
For example see Specification D 6359 for dry retroreflectivity reference standard deviate by more than 10 % from the initial
requirements. one, recalibrate and, in addition, re-measure previous measure-
4.6 For a given viewing distance, measurements of RL made ments.
with a retroreflectometer having a geometry corresponding to
that viewing distance are a good indicator of the visual ranking 8. General Procedure
of the material measured. 8.1 Both a dry and a wet measurement are usually taken in
4.7 As specified by Test Method E 1710, the measurement order to characterize the performance of the marking. The dry
geometry of the instrument is based on a viewing distance of measurement establishes the effectiveness of the marking in a

2
 E 2177
dry condition plus acts as a bench mark for the marking to 9.1.5 Identification of the pavement marking material
which the wet performance can be compared. However, the dry tested: type, color, age, and the location on road (edge line, first
measurement is optional per this test method. line, second line, centerline, etc.).
8.2 Measuring Dry or Wet Retroreflectance (RL) of Mark- 9.1.6 Identification of the instrument used, value and date of
ings: calibration of the reference standard panel used.
8.2.1 Use the manufacturer’s instructions for calibration and 9.1.7 Remarks concerning the overall condition of the line,
operation of the retroreflectometer. such as rubber skid marks, carryover of asphalt, snowplow
8.2.2 Locate the area of the pavement marking to be damage, and other factors that may affect the retroreflection
measured. measurement.
8.2.3 Place the retroreflectometer squarely on or in front of 9.1.8 Ambient temperature and other weather conditions.
the pavement marking material with the illumination in the 9.1.9 Description of roadway slope and general drainage
direction of travel. Ensure that the illuminated measurement where measurement is made (that is, puddles on marking due
area of the retroreflectometer fits within the width of the stripe, to low spot in road, water drained due to road incline, etc.)
and take a measurement. 9.1.10 Description of road surface and road texture, that is,
8.3 Measuring Retroreflectance (RL) in a Standard Condi- portland concrete cement (PCC) (broomed, brushed, worn),
tion of Wetness: bituminous, chip seal, etc..
8.3.1 Take a hand sprayer and wet the area of the marking NOTE 2—Pavement texture may be identified and quantified by Test
to be measured and the adjacent surrounding area (road surface Method E 965.
and marking) for 30 s. Verify that the marking and adjacent
area are completely flooded. Or pour 2 to 5 litres of clean water 10. Factors That May Influence Measurements
from a bucket. Slowly pour the water over the area of the 10.1 There are factors that may cause measurement vari-
marking to be measured plus the immediate surrounding area. ability when taking readings in the field. Some of these are:
The water is poured evenly along the test surface so that the 10.1.1 Slight changes in the position of the reflectometer on
measuring field and its surrounding area is momentarily or in front of the traffic line may yield different readings.
flooded by a crest of water (see Fig. 3). 10.1.2 The magnitude of the wet measurement obtained
may sometimes be dependent upon how well the water drains
9off from9 the marking. 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.

11. Precision and Bias

11.1 The precision and bias is based on three separate
FIG. 3 Illustration of Measurement studies, and their results can be found in Tables 1 and 2. The
tables show the repeatability for two instrument types and for
8.3.2 Measure the coefficient of retroreflected luminance, two levels of wet performance. One level of wet performance
RL, of the wetted marking 45 6 5 s after completion of is shown in Table 1 for values less than 100 [(mcd·m-2)/lx] and
spraying or pouring the water on the marking as described in the other level is shown in Table 2 for values greater than 100
8.3.1 (see Fig. 3). [(mcd·m-2)/lx]. The calculations and results follow Practice
8.4 Records—Record the dry and wet measurements in E 691.
millicandelas per square metre per lux, [(mcd·m-2)/lx]. Move to 11.2 In each study, the wet reflective measurement was
next measurement location which is separated sufficiently to performed by wetting the marking, waiting 45 s for the water
provide meaningful data and repeat procedures in 8.2 and 8.3. to drain and then taking the measurement. For each study, 2-3
9. Test Report replicate readings were obtained by simply triggering the
instruments a second or third time without moving the instru-
9.1 Include the following in the test report. ment (within 5 s). The wetting of the markings was done using
9.1.1 Test date. a sprayer. The instruments were calibrated before the studies
9.1.2 Average of the readings taken per line or marking were conducted.
expressed in millicandelas per square metre per lux
[(mcd·m-2)/lx]. The average of the readings shall be reported
for wet and for dry conditions and for each traffic direction of TABLE 1 Repeatability in Conditions of Wetness—for Values of
Wet Performance Under 100 [(mcd·m-2)/lx]
interest.
9.1.3 Readings for centerlines shall be taken for each NOTE 1—Individual readings range from 0 to 103 [(mcd·m-2)/lx].
direction of traffic. Readings for centerlines, edge lines, skip n Range of Mean Pooled Coef. of 95 % C.I.
lines, etc. Values Value St. Dev. Variation 2.8 (St. Dev.)
9.1.4 Geographical location of the test site. Global position- Study 1
ing system (GPS) location or distance from the nearest Instrument A 24 0 to 36 7.5 0.8 29.9 % 62.2
Study 2
permanent site identification, such as a mileage marker or Instrument A 17 4 to 98 52 4.2 22.7 % 612
crossroad.

3
 E 2177
TABLE 2 Repeatability in Conditions of Wetness—for Values of comparison of two instruments (A1 and A2).
Wet Performance Above 100 [(mcd·m-2)/lx]

NOTE 1—Individual readings range from 100 to 1174 [(mcd·m-2)/lx]. 12. Keywords
n Range of Mean Pooled Coef. of 95 % C.I.
Values Value St. Dev. Variation 2.8 (St. Dev.)
12.1 dry retroreflection; mobile retroreflectometers; pave-
ment markings; portable retroreflectometer; retroreflection in
Study 1
Instrument A1 14 97 to 1174 480 12.6 7.4 % 635 mcd wet conditions
Instrument A2 14 117 to 1150 460 14.6 8.9% 641 mcd
Study 2
Instrument A1 28 100 to 776 286 14.2 13.9 % 640 mcd

11.3 A reproducibility study (between instruments) has not

been completed. However, in Table 2 for values of wet
performance above 100 [(mcd·m-2)/lx], study #1 gives a

APPENDIX

(Nonmandatory Information)

X1. EXAMPLES OF PAVEMENT MARKING MEASURING SYSTEMS

X1.1 The entrance angle and observation angle specified in this test method are derived per the following geometry (which
exists in the vertical plane only). (See Fig. X1.1.)

FIG. X1.1 CEN 30 Meter Geometry—Pictorial of Observation and Entrance Angles for Simplified CEN Car

4
 E 2177
ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentioned
in this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the risk
of infringement of such rights, are entirely their own responsibility.

This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years and
if not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standards
and should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of the
responsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you should
make your views known to the ASTM Committee on Standards, at the address shown below.

This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,
United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the above
address or at 610-832-9585 (phone), 610-832-9555 (fax), or service@astm.org (e-mail); or through the ASTM website
(www.astm.org).