A study tested a vegetated biofilter to clean pollutants from simulated highway runoff. The biofilter was tested with different flow rates and slopes, mimicking storm events in Ohio. Results showed that the biofilter removed over 85% of metals and sediment, except for one metal in a specific test. Most pollutants were found in the first half of the filter. Soil particles in the runoff were not stirred up and did not show up in the outlet flow.