It's a little awkward, but what it's trying to communicate doesn't really work well in one sentence.
As a native US English speaker, I would probably write something like "Austria opens the world's sixth longest railway tunnel: 27 year long project arrives on schedule and under budget."
As a native US English speaker, I would probably write something like "Austria opens the world's sixth longest railway tunnel: 27 year long project arrives on schedule and under budget."
That's a long headline, though.