Researchers built different types of water treatment systems on a highway bridge in North Carolina to clean up the water that runs off the bridge. They found that the larger system was the most effective at removing pollutants like nutrients and sediment from the water. The smaller system also helped, especially in areas with limited space. A grassy swale was less effective at cleaning the water compared to the other systems. Overall, the larger bioretention cell reduced the amount of pollutants in the water the most, while the smaller cell was a good option for smaller spaces.