Bridges, especially overpass models, differ from railroads as they are three-dimensional rather than flat. Therefore, an interlaced sense of depth needs to be created, primarily through varying shades of color, contour lines, and shapes. There are two main methods: the three-dimensional method and the flat method. The flat method is typically used when bridges are considered accessories. To showcase the bridge itself, the three-dimensional method is generally employed, as it clearly demonstrates the size and elevation of the bridge. Specific techniques include:

1. Hierarchical Representation: Employ contour lines to depict the height, dimensions, and levels of the bridge. During painting, the color transitions from light to dark from top to bottom, creating a shadow effect for a more realistic visual appearance.

2. Width Representation: During the construction of bridges, visual errors can be utilized to differentiate widths, rather than strictly adhering to proportional reduction. Instead, certain widths can be intentionally exaggerated to create a visual distinction in the width perception of the bridge.

3. Perspective Representation: Since we typically view models from above, the green belts and guardrails on both sides of the bridge should be made taller to ensure they are visible.

4. Fixed Model: The completed model must be securely fastened to the base, allowing for segmented adhesive application. This ensures that each section is not overly long and that the joints are reinforced, ensuring the model remains stable.