201007 – Sanchez – ATP Update Transponder Positioning

The PTAWA (Public Transport Authority of Western Australia) introduced the Ansaldo L10,000 ATP
system (also known as ATC1 or EBICAB) into its rail network in 1990/1991.

From the beginning, a point of contention between the PTA and its contractors has been the
positioning of ATP Update Transponders. The number and placement of transponders required to
minimise the „delay effects‟ caused by the use of discrete information points as “infill”, or the need for updates at all, will be examined This paper will demonstrate the different methods used by the PTAWA to determine the positioning and number of ATP Update Transponders between signals.

The use of Update Transponders as “Infill” seems also to be losing favour in the signalling world due to the perceived delay effects caused by intermittent systems. A new method of determining Update Transponder positioning is proposed which demonstrates that intermittent systems can provide good performance at a reasonable cost.

Most of this document and calculations assume the use of the Ansaldo L10,000 system as installed in
the PTA. Many of the concepts and ideas may be directly translated to other intermittent ATP systems
such as ETCS level 1.