Safety Enhancement of the INDOT Network Pavement Friction Testing Program: Macrotexture and Microtexture Testing Using Laser Sensors

The Indiana Department of Transportation has conducted annual network inventory friction testing using the locked wheel trailer to reduce wet pavement crashes. However, issues have arisen concerning the data credibility and field operation safety on high-speed highway facilities. Some researchers have investigated the evaluation of pavement friction using macrotexture measurements and found the relationship between friction and macrotexture is extremely weak. Currently, macrotexture can be readily measured at highway speeds, but microtexture is evaluated using friction at low speeds from a surrogate device. Microtexture plays an important role in friction force. The evaluation of pavement friction from texture measurements will be undermined without considering microtexture. This pilot study was conducted by the authors to examine the use of laser-based sensors in measuring pavement texture, in particular microtexture. The requirement for laser sampling frequency was established for choosing lasers during testing at highway speeds. Microtexture testing was conducted on cores taken from pavements. It was found that the Microtexture MPD, RMS and SV increased as the baseline length increased, regardless of the type of pavement, but tended to remain constant after the baseline length exceeded 12.75 mm. It was recommended that the microtexture MPD, RMS and SV should be computed in terms of a baseline length used for computing macrotexture. When estimating friction from microtexture measurements, the use of SV was as effective as the use of RMS. It is not necessary to include both SV and RMS when estimating friction from microtexture. Correlation analysis indicated that wet pavement friction had a positive relationship with macrotexture MPD, microtexture MPD, and microtexture SV. The microtexture SV may play a more important role in wet pavement friction than the microtexture MPD. Dry pavement friction is not as sensitive to macrotexture as to microtexture. Regression analysis indicated that pavement friction is related to both macrotextrue and microtexture, not to macrotexture only. In addition, when pavement is wet, its surface friction is more sensitive to the slope variance than to the mean profile depth of the microtexture profile. It was recommended that more research effort is needed to investigate the characterization of microtexture and examine the effect of macrotexture slope variance. Research work is also needed to examine the image processing technology for measuring microtexture, and to confirm the hypothesis that pavement friction is probably related to microtextures with wavelengths greater than a certain value