Imagine you are comming from direction of arrow next to 1.
The left turn on yellow intersection(1) is not possible in real. On (2) i noted all relavent nodes that can be blocked, i am unable to block left turn.
Please let me explain how it works. We provide free software, but do not make maps. Free maps are created by volunteers at www.openstreetmaps.org - anybody can join and help to make maps better using their local knowledge. May be you can also contribute?