Minnesota Department of Transportation
Concrete pavements built in Minnesota are currently textured by dragging an inverted Turf or broom in the longitudinal direction. This process imparts a macro texture required to be greater than a mean texture depth of 1mm measured by the ASTM Sand Volumetric test (ASTM E 965-95). At present, this texture guideline is communicated through a special provision in pavement construction. Newly textured pavements are usually evaluated for adequacy in providing a safe riding surface through texture measurements for acceptance and friction measurements as required. The current FHWA Technical Advisory on Texture requires that performance of non-conventional textures be monitored and reported. This report identifies pavement sites in the network where the original texture, mainly the transverse tining plus Burlap, was either overlaid or rebuilt and the new surface finished with longitudinal inverted turf drag, or broom drag. It extracts wet weather accident data from the Mn/DOT Office of Traffic, Safety and Operations (OTSO) database and analyzes the annual wet weather accident and crash rates, preconstruction, during construction and after construction. It performs a descriptive statistics of the period before and the period of the new texturing to determine if, wet weather accident counts, percentage of wet weather accidents in total count and crash rates and /or ratio of annual wet to dry accident counts, and crashes clearly increased with current texturing practices. Data was analyzed with statistical tools for data comparison including the descriptive statistics, U-test & and "before and after" comparison (Z-test). The analyses of the data for the sections show that current texturing practices did not cause an increase in the annual wet weather accidents, crash rates, or ratio of wet to dry weather accidents.
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