Despite being pretty fully signalled by the looks of things, the signalling on this run was being run on the key principle – that's where you have the physical authority to run on a line because you possess the "keys to the line".  If you don't have the keys for a segment of track, you have no right to be there.  This might sound positively antique and perfect for a heritage line, but some parts of the British railway system still run on this system – the line between St Erth and St Ives for example.
<a rel="nofollow" class="external text" href="https://www.flickr.com/people/54741099@N00">Andrew Bowden</a> from London, United Kingdon
CC BY-SA 2.0
<a rel="nofollow" class="external text" href="https://www.flickr.com/photos/bods/2982734264/">Keys to the line</a>