In the PIARC International Experiment ( 1³ ) it was found that the volumetric mean texture depth (MTD) was highly correlated to the speed constant of the International Friction Index. It has been found that the average of the MPD values for the eight segments using the CTMeter is extremely highly correlated with the MTD and can replace the volumetric measurement for determination of the MTD (2). The recommended relationship for the estimate of the MTD from the MPD by the CTMeter is:

when MTD and MPD are expressed in millimetres,

or:

when MTD and MPD are expressed in inches.

Note 1—These equations differ from those given in Practice E 1845, which are for the estimated texture depths from linear profiles.

Comparison of the MPD and the RMS for a surface provides information of the nature of the texture, that is, whether the texture is positive or negative ( 3).

Analysis of the individual segments can be performed to examine the profile parallel to the direction of travel (segments A and E) and perpendicular to the direction of travel (segments C and G). This information could be particularly useful in the study of surfaces that have texture with significant directional characteristics.

1.1 This test method covers the procedure for obtaining and analyzing pavement macrotexture profiles using the Circular Track Meter (CTMeter).

1.2 The CTMeter consists of a charge coupled device (CCD) laser- displacement sensor which is mounted on an arm that rotates such that the displacement sensor follows a circular track having a diameter of 284 mm (11.2 in.).

1.3 The CTMeter is designed to measure the same circular track that is measured by the Dynamic Friction Tester (DFTester).

1.4 The CTMeter can be used both for laboratory investigations and in the field on actual paved surfaces.

1.5 The software developed for the CTMeter reports the Mean Profile Depth (MPD) and the Root Mean Square (RMS) values of the macrotexture profiles.

1.6 The values stated in SI (metric) units are to be regarded as standard. The inch-pound equivalents are rationalized, rather than exact mathematical conversions.

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.