Zie toelichting uit WIKI:
Overlapping road junction
Two roads set to the same level which cross each other can be joined by an intersection easily. This is useful if you draw several new roads for a neighborhood by drawing segments from end-to-end and allowing new segments to cross each other. Once drawn, you can junction them using this method.
Both roads must be set to the same level. You can often use this method with unconfirmed (red) roads, but sometimes the editor will refuse to do this process until the roads are confirmed. Additionally, changing zoom level sometimes helps to get a stubborn yellow crossing sign to appear.
Select both segments
Click the which should appear above the intersection
Note: The sign won’t appear if the roads cross each other multiple times
A junction is added
EDIT
fvwazing was mij voor 