This setting enables you to build bridges at any height, not just one tile above the ground.
Originally, bridges could only be built at one-level above the ground they are spanning. With this patch, it is possible to place bridges which span deeper gaps, as the picture shows.
Like normal bridges, this patch allows one end of the bridge to be started from a lower tile, provided the tile is flat. This patch does not allow 'sloped bridges' (e.g. bridges that start from a height of 1 and end at a height of 3).
By default, when a higher bridge is built, pillars underneath the bridge are shown to the ground. You may disable these by using the bridge pillars patch.
This patch is always enabled and is not configurable.