Preliminary Results: Measurement of Macrotexture on Surface Treatments and Survey of Bicyclist Ride Quality on Mon-198 and SLO-1 Test Sections

This memorandum summarizes the results of measurements of macrotexture on a set of Caltrans pavement surface treatments, and the results of bicycle vibration measurements and a survey of bicyclists ride quality on a subset of those sections. The work was performed to address concerns raised by local bicyclists regarding the ride quality after a modified binder seal coat (chip seal) was placed on State Route 1 in San Luis Obispo County (SLO-1). The subset includes test sections for various surface treatments on existing chip seals on State Route 198 in Monterey County (Mon-198) and several locations on SLO-1. Macrotexture was measured in terms of mean profile depth (MPD). Three different test methods were used to measure MPD: the sand patch method and the laser texture scanner (LTS), which provide measurements on a small area at a single location (about 12 square inches [100 square cm]); and the inertial profiler (IP), which is mounted on a vehicle and provides a continuous measurement in the longitudinal direction. Also presented are preliminary statistical correlations between macrotexture, bicycle vibration, and bicyclist ride quality for the initial set of treatment sections surveyed to date, and preliminary modeling of the relationships between macrotexture, vibration, and perceived ride quality for bicyclists. Conclusions are presented regarding the MPD values measured on various road sections including those built with two 3/8" aggregate gradation chip seal specifications (one coarser than the other), and the variability of MPD found between sections built using the coarser 3/8" aggregate grading. Conclusions are also presented regarding the three MPD measurement methods. Findings are presented regarding the MPD values from other types of treatments, including possible treatments to be placed on SLO-1 to address bicyclist ride quality issue. Results are also presented regarding the effects of trafficking on MPD values. Correlations between bicycle vibration and MPD are shown, and between MPD, bicycle vibration, and bicyclist perception of ride quality and acceptability for use by bicycles. Recommendations are made regarding the use of additional rolling to reduce the texture of chip seals built using the coarser 3/8" aggregate grading, a preliminary range of MPD values that might be used to select chip seal specifications based on “acceptability” where bicyclist ride quality is an issue, and selection of remedial treatments for SLO-1 based on the Mon-198 test sections