OpenRoads Designer Earthwork

you can add an overlay component to the bridge deck bottom. Top of Overlay to follow component, Bottom of Overlay to follow Existing Terrain. Be sure that Overlay Componts has a feature definition with a volume option set to Design. Then with this solution the void under the bridge will be filled with "dummy" design material and no Fill will be there. Neither in dynamic cross-section nor generated with Create Cut Fill Volumes tool.

you can add an overlay component to the bridge deck bottom. Top of Overlay to follow component, Bottom of Overlay to follow Existing Terrain. Be sure that Overlay Componts has a feature definition with a volume option set to Design. Then with this solution the void under the bridge will be filled with "dummy" design material and no Fill will be there. Neither in dynamic cross-section nor generated with Create Cut Fill Volumes tool.