{'fraction_non_alphanumeric': 0.01435670900055218, 'fraction_numerical': 0.0, 'mean_word_length': 5.448398576512456, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
State of the Practice Permeable Friction Courses

Permeable Friction Courses (PFCs) are open-graded bituminous mixtures placed over an impervious base. The interconnected air voids allow rainwater to drain into the pavement thus providing a safer driving surface in wet weather and a filter for highway runoff. This report summarizes the current state of the practice related to the hydraulic properties, water quality benefits, and maintenance of PFCs based on literature from around the world. Porous pavements reduce pollutant concentrations in the highway runoff during the functional service life of the pavement, which ultimately results in the clogging of the pavement. This material accumulating in the pores was found to have high concentrations of pollutants, such as heavy metals. Pavement cleaning machines used in Europe to remove accumulated pollutants are described and usually found to maintain the function of the pavements. Existing research also includes measurements of hydraulic conductivity over time and from different pavements. In winter conditions, more maintenance is required for PFCs than for conventional pavements since the air voids change with ambient air temperature causing the PFC to freeze faster than conventional pavement. Other beneficial properties of PFCs, such as the friction coefficient and noise reduction ability, are also described. This report also presents the results of a nationwide survey of state departments of transportation (DOTs) conducted to document PFC use and maintenance in the United States. The survey revealed minimal hydraulic testing, hydraulic design guidelines, and pavement maintenance by the DOTs. The cleaner stormwater runoff observed from PFC in several European studies has not been investigated by state DOTs other than the Texas DOT.