Systems, methods and computer storage apparatuses for synthesizing terrain elevations under overpasses are described herein. An embodiment includes identifying one or more spans across an overpass in an overpasses model, where the overpasses model includes information for one or more overpasses and respective locations and widths of the spans. The embodiment associates one or more terrain elevation values with the one or more identified spans, where the terrain elevation values can be included in an elevation model corresponding to the overpasses model. The embodiment further includes interpolating terrain elevation values for one or more points across the identified spans and updating the elevation model with the interpolated terrain elevation values.