Bridge Modeler (or Bridge Module) for Autodesk Civil 3D is a specialized extension designed to integrate bridge engineering into civil infrastructure workflows. However, its availability and the method to "download" it have changed significantly over the years. Availability and Versioning Discontinued for Modern Versions
Depending on your software version, you can access bridge modeling tools through the following methods: Civil 3D Workshop - Using Dynamo to Enhance Bridge Projects Bridge Modeler Civil 3d Download
Civil 3D remains the master of the road. Bridge Modeler (or Bridge Module) for Autodesk Civil