It understands \n if I recall correctly. You can also write regular bash, use templating tools, etc. Just use the nativeBuildInputs parameter if you need a binary that isn't provided by stdenv.

It doesn't help that US diverging diamonds seem to insist on having pedestrians walk through the median.

But honestly all interchanges are varying degrees of horrible and if you want your city to be bearable to navigate as a pedestrian/cyclist you just really don't want to do urban highways, or roads above a certain size in general.