Re: Signalling queries - Jointless tracks

["Chris Downs" <cvdowns@ozemail.com.au>]

Eddie Oliver <eoliver@efs.mq.edu.au> wrote in message
3B25F092.4F3DBC5C@efs.mq.edu.au">news:3B25F092.4F3DBC5C@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.

These were also used for certain signals between Erskineville and Sydenham (&
beyond?) when resignalled.  Considering the location of the DPUs in advance of
certain signals, this forms part of the approach release system for these
signals?

Chris