Elon Musk's plan to tackle traffic using a huge tunnel boring machine (TBM) appears to be in full swing. The billionaire SpaceX and PayPal founder tweeted this photo showing the rear of a TBM, with the excavating conveyor belt which removes the debris from the site clearly visible in the bottom centre of the image. Musk has yet to confirm, however, whether the image of the tunnel boring machine he tweeted is his own, or what its exact purpose.