The area outside the white grid cannot be built on in the asset editor. With the mod "Fine Road Anarchy" you can make this grid disappear, which allows to create huge intersections.

Many "real-life intersections" are difficult to realize in Cities: Skylines, as the asset editor often does not give the size for such projects. Especially when it comes to extended freeway entrances and exits, you can reach the limits of the editor.

The mod Fine Road Anarchy makes it possible to place roads with no restrictions on steepness, shape and distance to other objects. As soon as you have subscribed to the mod, check in the menu whether it is also activated.

Toggle Editor Grid in the Asset Editor with Fine Road Anarchy.
The editor grid can be deactivated in the mod's toolbox.

To build beyond the limits of the asset editor, the editor grid must be deactivated. To do this, click on "Toggle editor grid".

Big intersection in the Asset Editor with the Mod Fine Road Anarchy.
Building freely is possible without the editor grid.

Now that the grid is deactivated, your building space is unlimited. The camera can also be moved freely and no longer stops at the edge of the editor.

Cities Skylines: How to Update Steam Workshop Items
This post will briefly explain how you can update an existing item in the Steam Workshop. This guide works for all items, including savegames, maps, assets, mods, themes, scenarios, and so on.
Guide for updating items, that are already uploaded to the Steam Workshop.

The intersection in this post does actually exist, it is located in the US state of Florida. You can download it in the Steam Workshop:

Florida Turnpike - Steam Workshop