How can you make a sunken highway in SimCITY 4?

To create a sunken highway in SimCity 4, first, use the "Terrain" tools to lower the land where you want the highway to be. Next, construct a highway using the "Road" tool, placing it in the lowered area. You may need to adjust the surrounding terrain or use the "Elevated Highway" option to transition smoothly between levels. Finally, adding decorative features like trees or parks can enhance the aesthetics of your sunken highway.