![Big announcement, bigger plans: Elon Musk.](http://web.archive.org./web/20170721024101im_/https://www.fairfaxstatic.com.au/content/dam/images/g/x/f/5/t/a/image.related.wideLandscape.460x259.gxflg1.png/1500597275835.jpg)
Elon Musk claims approval to build world's longest tunnel
With a tweet and very little else by way of detail, entrepreneur Elon Musk has raised the prospect of building the world's longest tunnel for an ultra-high-speed train line to connect New York to Washington.