QGIS Geometry Generator for SimCity Style Bridges

simcity_bridges.txt

-- add this to a road LINE layer that also has
-- a geometry geometry applied that buffers it
-- by 1000m. That's wide, I know!
-- change the reference to your water layer below.
-- all layers must be in a projected crs.

collect_geometries(
    array_foreach(
        geometries_to_array(
			intersection(
                nodes_to_points(
                    densify_by_distance(
                        collect_geometries(
                            array_foreach(
                                geometries_to_array( 
                                    segments_to_lines( $geometry)
                                ),
                                if(
                                    line_interpolate_angle(@element, 100)>180 AND 
                                    line_interpolate_angle(@element, 100)<360,
                                    offset_curve( @element, 1000),
                                    offset_curve( @element, -1000)
                                )
                            )
                        ),
                        2000
                    )
                ),
				collect_geometries(
                    overlay_intersects(
                        layer:= 'ADD_REFERENCE_TO_WATER_LAYER_HERE', 
                        expression:= @geometry
                    )
                )  
            )
        ),
		make_line(@element, translate(@element, 0, -1000))
    )
)