|man_made = gantry|
|An overhead structure across a major road usually for holding signs, often variable-message signs.|
|Used on these elements|
|Status: de facto|
|Tools for this tag|
A highway gantry is an overhead structure across a major road usually for holding signs, often variable-message signs.
Draw a line representing the gantry, using the base of the gantry as nodes. Just like you would with a bridge, do not connect the gantry to the way it is crossing, and also add an appropriate layer=* tag.
For the original proposal see here.