The idea is to add information to the route network in the LRS Data Model as appropriate to model the grade elevation of highway intersections. One way to achieve this would be to add elev_begin and elev_end to the centerline and to the route network, where the values would consist of either the interpolated Z values or enumerated grade (0 - at grade, 1 first overpass, 2 second overpass intersecting over 1 first overpass, etc) integer values.
This information would be used to model and cartographic display the appropriate over/under for grade separated interchanges, as well as to help define the spatial/logical relationship of intersections between at-grade and grade-separated. This information would especially be helpful in visualization and routing to be derived from the LRS data model, considering all events registered to the route network should belong to the routes at the proper network elevation level, especially including tunnels and bridges as linear events, which further serve to indicate the route over/under relationship.
