The State of Hawaii Department of Transportation, Highways Division, Oahu District (DOT-HWYS) is nearing the completion of its two-year data collection period for its Debris Cleaning Assessment. In October 2014, DOT-HWYS embarked on a study aimed to better understand how effective street sweeping is in reducing pollution from our highways. Street sweeping has been identified as one of the most cost-effective highways debris removal practices and keeps our highways and storm drains free of pollutants.

Over the two-year period, DOT-HWYS has collected more than 80 samples of street sweeping debris and had the samples analyzed by a certified laboratory for their grain size distribution, bulk density, moisture content, nitrogen content and phosphorus content.

A better understanding of the composition of the debris removed will enable DOT-HWYS to develop a more efficient street sweeping program to keep our highways clean and improve water quality.

Street sweeping samples
Street sweeping samples. The left sample is from a vacuum sweeper that uses suction to pick up debris. The right sample is from a mechanical sweeper that uses a main broom to pick up debris.

 

Note that the vacuum sweeper is able to pick up finer particulates, which commonly have a higher concentration of nutrients — like phosphorus and nitrogen, which can cause algae blooms harmful to marine life — attached to them. DOT-HWYS utilizes both mechanical and vacuum sweepers in tandem to maximize street sweeping efficiency.