REGISTER

JT Skilton

BE (Elect) Hons., MIPENZ

Signals and Telecommunications Projects Engineer

Tranz Rail Ltd

Signalling systems within Tranz Rail which require control from a remote location can be classified into three types, Centralised Traffic Control (CTC), remote controlled interlockings in Track Warrant (TW) territory and remote controlled interlockings embedded in Double Line Automatic (DLA) signalling.

The CTC systems control the movement of trains in both directions over a single line section divided up into block sections and crossing loops. A field unit is installed at each crossing loop for the purpose of communicating with the control centre.

TW control requires all trains to hold a warrant for the section of line being traversed. This warrant is issued to the locomotive engineer verbally over the train radio system and checked for correct reception by reading back over the radio system to the control centre. A selected number of crossing loops within TW territory are fully interlocked and equipped with a field unit which allows the Train Control Operator (TCO) to have full control over motor points and signals.

Centralised control of interlockings in DLA territory is used where junctions between main and branch lines occur. Central control is used for movements to and from the branch line and, although it can also be used for signalling along the main lines, the interlocking can be switched to automatic for main line movements.