In BrD and BrR, a bridge is a group of structures providing continuity of a highway across an entire crossing. A bridge alternative is a configuration of superstructure and substructure units making up the physical definition of a bridge. BrD and BrR allow the user to define more than one mutually-exclusive bridge alternative for the same bridge, a feature useful for comparing design alternatives. For example, a two-span bridge can be compared to a one-span bridge for the same crossing. Each mutually-exclusive alternative configuration for a bridge is called a Bridge Alternative. The following sketch illustrates alternatives.
It is very important to create a bridge alternative, a structure, a structure alternative, and a superstructure definition assigned to a structure alternative so that the bridge can be rated from the Bridge Explorer in BrR. The steps involved in rating bridges from the Bridge Explorer in BrR are described in Rating from the Bridge Explorer. The ability to rate bridges from the Bridge Explorer is very useful for performing a permit route analysis and to analyze vehicles over a group of bridges along a specific route.
When rating from the Bridge Explorer, BrR will rate all appropriate member alternatives for each selected bridge. To do this, BrR searches for bridge components that are marked as "Existing". BrR uses the bridge alternatives marked as existing and rates each structure in that bridge alternative. For each structure, BrR reviews the structure alternatives marked as existing and for each structure alternative BrR reviews at the superstructure definition assigned to it. For the superstructure definition, BrR continues to review member alternatives within the superstructure definition that are marked as existing. If the Bridge Workspace tree does not contain bridge alternatives, structures, structure alternatives, superstructure definitions assigned to structure alternatives and member alternatives marked as existing, no rating will be performed for that bridge.