In the next 6 years under a Metro each of these wheels will travel more then 20 times round the world - (over a million miles)
<a rel="nofollow" class="external text" href="https://www.flickr.com/people/12349133@N05">djminisite</a>
CC BY-SA 2.0
<a rel="nofollow" class="external text" href="https://www.flickr.com/photos/12349133@N05/5130990223/">Sets of axles being overhauled and inspected</a>