This is the train that never carries passengers. Meet Dr. Yellow, Japan's legendary high speed train that serves one very special purpose. Ensure that all rail tracks and train paths are healthy and can be used from the very next morning. It can move at more than 600 km per hour, more than double the speed of a regular high speed train. Tickets can't be bought as the train is full of sensors and different machines that recover raw data from the tracks, like stability and integrity. When it detects something is wrong, it immediately sends an SOS signal so that engineers go and repair the issue. Did you know about it?