Comparative Evaluation of Alternative BPTs in Assessing Tire Skid and Pedestrian Slip Resistance on Pavement Markings with Integrated AIMS, FFT, and Microscopy Analyses

Abstract Sufficient friction is needed by pedestrians and vehicles for crosswalk safety. A few studies have been conducted to correlate pedestrian slip resistance (PSR) and tire skid resistance (TSR) on pavement markings. This research assessed the ability of two alternative British pendulum tester (BPT) units in comparative measure of the skid and slip resistance of pavement markings. The side-by-side comparison of the two BPT devices provided 216 British pendulum number (BPN) values for 18 asphalt and concrete samples of three marking types: preformed thermoplastic P, high-performance tape T, and thermoplastic Th, on dry, wet, and icy surfaces, and with six replicates in each condition. Results were highly repeatable and reproducible. Coefficients of variation were under 2%. Paired <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="t" display="inline" overflow="scroll"> <mml:mi>t</mml:mi> </mml:math> -tests and analysis of variance/multivariate analysis of variance revealed no significant differences by operators or devices ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="p greater than or equals 0.05" display="inline" overflow="scroll"> <mml:mi>p</mml:mi> <mml:mo>≥</mml:mo> <mml:mn>0.05</mml:mn> </mml:math> ). Friction response followed expected trends: for dry TSR, T markings had the highest BPN values, followed by Th markings and P markings. Comparing measurements on surfaces of new versus old pavement markings, TSR declined by around 18% in T, 12% in Th, and 10% in P. Microscopy complemented these findings with “ground truth” conditions, exhibiting bead retention for T, bead loss for P, and smearing for Th. Fourier analysis differentiated the major contributions of texture. Macrotexture dominated P at approximately 0.9 to 1.2 mm. T yielded a combination of micro- and macro-texture at approximately 0.3 to 0.5 mm. Microtexture dominated Th at approximately 0.15 mm, and macrotexture affected PSR at approximately 1.0 mm. Aggregate image measurement system (AIMS) texture measurements were in good agreement with BPN. <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="upper R squared" display="inline" overflow="scroll"> <mml:msup> <mml:mi>R</mml:mi> <mml:mn>2</mml:mn> </mml:msup> </mml:math> values of exponential models were between 0.884 and 0.945. Pairwise correlations of marking types were more than 0.92. These findings establish that the BPT units yield consistent TSR and PSR values on crosswalk markings. The analysis approach in this study, integrating microscopy, Fourier analysis, and AIMS analysis to BPT measurements, provides an innovative approach for relating slip and skid measurements to the “ground truth conditions,” and thus a better understanding of the “wear and tear” effects under traffic on pavement markings that eventually may lead to better selection of such materials.