Factors affecting highway runoff quality

Highway runoff often is a significant non-point pollution source. Though it has been extensively studied there are still open questions regarding the identity and mutual influences of the factors affecting pollutant concentrations in road runoff. This review starts with a description of the main pollutants (heavy metals, refractory organics and suspended matter), then it analyzes interactions existing between them and their fractionation between the particulate and dissolved phases. The third section examines the sources of pollution, being: vehicles which contribute fluid and solid pollutants, roads which contribute suspended solids, and dry and wet atmospheric deposition which is influenced by adjacent land-uses. The last section discusses the importance of the factors affecting road runoff quality, the main of which are traffic, rainfall, local conditions (climate and land use) and highway characteristics. The review reveals that conclusions derived from existing data are often ambiguous and significant knowledge gaps still exist.