Summary

Nonpoint source pollution is common in highly developed areas worldwide, degrading downstream water quality conditions and causing algal growth, aquatic toxicity, and sometimes fish kills. Stormwater runoff that results from rainfall or snowmelt events creates high-flow runoff from impervious surfaces and adjacent areas transporting multiple pollutants to the receiving waters. Although water quality regulations in the developed world have been effective in cleaning up wastewater discharges, their success with remediating stormwater discharges has not been consistent. An exploration of the sources, characteristics, and treatment of roadway runoff, a type of runoff that can be toxic and more difficult to manage because of the linear nature of the road network, is necessary.

Since 1975, there have been more than 50 major roadway studies quantifying the sources and types of runoff contaminants like sediment, metals, inorganic salts, and organic compounds. Vehicle sources of pollutants are considered the most pernicious of all roadway contaminants, with brakes and tires being major sources. In the last decade, the leachate from tire wear particles has been linked to toxicity in coho salmon. Nonstructural stormwater management minimizes contamination by using source controls; for example, the elimination of almost all lead in automotive fuel has reduced roadway lead contamination significantly and the introduction of low-copper brake pads in the United States is expected to reduce roadway copper contamination over time. Structural stormwater management practices treat contaminated roadway runoff using small natural treatment systems; this is due in large part to the linear nature of roadways that makes larger regional systems more difficult. Since 2000, treatment performance has improved; however, there is still a great need for further improvement. Suggestions for treatment improvements include designing with low maintenance in mind; applying machine learning to the existing data; improving the understanding of road-land pollutant dynamics; using a transdisciplinary applied research approach to identify the means to improve treatment and reduce toxicity; improving the media used in treatment systems to enhance performance; improving structural strength of permeable pavement; and increasing implementation by facilitating ways to allow/encourage small, effective, and less costly alternatives.