''What is an overpass?'' An overpass is a general term for any road, walkway, railroad, bridge, or other mapped structure crossing over an impediment such as a waterway, natural formation, or another road, walkway, railroad, or bridge. In our mapping context it can also be conceptualized underground where tunnels crossing over, or under, one another.
=== Elevation ===
Apply these points to the use of true elevation:
:* All roads when not supported above or tunneled below the terrain are set to ground elevation unless otherwise noted.
:* Ramps are to be set to the lower elevation of the roadways to which they junction unless passing over or under other segments.
=== Segmentation ===
When creating segments to implement this guidance, please observe these precepts:
:* Create junction nodes for elevation purposes at the point the physical change in elevation occurs unless otherwise specified.
:* Check the tunnel option for any underground segment.
=== Culverts ===
A ''culvert'' is a tunnel allowing a stream or open drain to pass under a roadway. Under normal circumstances these are not to be mapped. However, an elevated segment for a culvert may be created to support real-time closures (due to significant flooding or repair) when '''all''' these conditions are met:
:* The culvert is of significant construction requiring multiple day closures to repair or has major flooding potential.