Bridges, especially overpass models, differ from railroads as they are three-dimensional rather than flat. Therefore, to create an interlocking sense of depth, color gradients, contour lines, and shapes are primarily used, with specific techniques divided into three-dimensional and flat production methods. The flat production method is typically used when bridges are accessories, while the three-dimensional method is generally employed to showcase the bridge itself, clearly illustrating its size and elevation. The specific methods are as follows:

1. Hierarchical Representation: Utilize contour lines to depict the height, dimensions, and levels of the bridge. During painting, colors transition from light to dark from top to bottom, creating shadows for a more realistic visual effect.

2. Width Expression: During the manufacturing of bridges, the width can be emphasized through visual illusions, rather than strictly following a scaled-down proportion. Some widths can be intentionally exaggerated to create a distinguishable sense of width visually.

3. Perspective Representation: Since we usually 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: Once the model is completed, it must be securely fastened to the base platform. This allows for piecemeal application of adhesive, ensuring that each section is not overly long and that the joints are reinforced for stability.