&quot;A future this or any other transport technology lacks in Japan, for the Tōzai line is almost certainly the last subway line Japan will ever build.&quot;<p>&quot;Ever&quot; is a very, very long time! There might not be any new subways for a few decades, but the idea of a &quot;subway&quot; itself is only about a hundred and fifty years old. How could one possibly know whether Japan will need new subways in seven hundred years? And seven hundred years is just an eyeblink, compared to &quot;ever&quot;. The human species is about a hundred thousand years old, and most animals have been around for far longer than that.