Re: Signalling queries - Jointless tracks

[Eddie Oliver <eoliver@efs.mq.edu.au>]

Chris Downs wrote:

> With the mass resignalling of the Sydney suburban network just what sections
> of track use insulated track joints now?
> Penrith - St Marys (both rails) [seems unusual]
> "Strathfield Box Area" (one rail)
> "Sydney Box Area" (one rail); bar underground, ESR, Airport Line
> ..................?

Trying to generalise: in areas with little complication (e.g. open
track) the tendency is to go to jointless tracks when it can
conveniently be done, e.g. in conjunction with track upgrading. The East
Hills line, for instance, has been largely de-jointed in the last couple
of years. However some areas of high complexity do not naturally lend
themselves to jointless tracks, one reason being that the precise
beginning and end of a circuit are not defined to pinpoint accuracy in
jointless tracks.

A supplementary technique is the use of DPUs (data pick-up units) which
can subdivide a track circuit. These things, which look like metal ramps
alongside one rail, can be seen along some of the city stations, for
instance. If a track circuit is occupied, these things can tell whether
the occupancy is on one side or the other relative to their own
location.