The railway is
single track, so special measures have to be taken to prevent collisions. Before preservation, the railway operated a "
one engine in steam" policy, but with growing passenger numbers it became necessary to install passing loops and a more stringent method of single line control was introduced.
[93] The line is worked by Electric Key
tokens, which authorise the driver to enter a section of single line, and these are interlocked to prevent more than one token being withdrawn for a section at any one time. There is a loop at Pendre, which was used from the opening of the railway for shunting purposes, and further loops were installed at Brynglas in 1953 and Quarry Siding in 1963.
[94] When the Nant Gwernol extension opened in 1976, Abergynolwyn also became a passing loop.
[95]
Each passing loop is controlled by a small
signal box, known as a block-post. These house the lever frames that control the points, the token equipment and telephones. The railway has few signals; instead it has stop boards at Pendre, Brynglas, Quarry Siding and Nant Gwernol, and the
blockman allows trains to proceed by use of flags.
[96] There are colour light signals located at Tywyn Wharf, operated from the Control Office and disc signals controlled from the ground frame. Abergynolwyn has colour light signals, which are operated from the blockpost.
[97] When the block-post is unmanned, it is the responsibility of the locomotive crew to change the token before proceeding.
[98]