What do you call this elevated road structure?

"Overpass"

noun
1. A road, pedestrian walkway, railroad, bridge, etc., crossing over some barrier, as another road or walkway.

www.dictionary.com

In Britain, this is known as a flyover.

One road flies over another. Sometimes, overpass is used but this is much less common.

Well, it all depends on what specifically you want named. As a civil engineer with bridge design experience, I'm happy to provide the technical terms.

The exact bit where one road passes over another is called a bridge. (No, a bridge does not have to pass over a "natural feature"). But the term "bridge" doesn't cover the ramps either side - these are approach embankments supported by mechanically stabilised earth walls.

To describe the whole thing, the previous answers of overpass or flyover would both be valid engineering terms. For this particular case, where the structure carries traffic which is avoiding a junction of the road it is travelling on, flyover would be the most typically used in the UK.

I think it is also called road bridge:

• a structure spanning and providing passage over a gap or barrier, such as a river or roadway.

  • something resembling or analogous to this structure in form or function:

(TFD)