A colour light signal capable of displaying four aspects. From top to bottom the lights are yellow, green, yellow, and red. A red indication means that the next section contains a train. A single yellow indication (using the lower yellow) means that the next section is clear but there is a train in the following one. A double yellow indication means that the next two sections are clear but there is a train in the one beyond that. A green indicates that the next three sections are clear. Depending on the speed of the train, it will need to commence slowing on either a single or double yellow.