Center Passing Track - options

[Texas Zepher]

jeffhergert

Speed restrictions would depend on the size of the turnout, not what type it is. 

Yup, and remember a wye turnout departure size is actually twice the frog measure.  That is a number #3 wye is the equivalent of a #6 normal left or right turnout.   A #4 wye would match a #8 straight.  etc.

 

Here is a center passing track.  The turnoff from the main line is under the rear truck of the 6th car back (last streamlined before the two heavyweights).

Here is another entrance to a center passing track, this time front and center.

 

[dehusman]

 

Most center sidings I have seen were accessible from both main tracks on both ends.  Most used a "normal" switch on the mains and equitlateral (wye) switch on the siding.  Most were also speed restricted (10 mph) going into the siding and no speed restriction on the mains.  They are used to clear a freight to allow a faster train to pass or to hold a train waiting to operate against the current of traffic (since most double track lines were at one time rule 251, current of traffic operation).

[markpierce]

Hudson

If you have to kick out the two main tracks in order to place a passing track in between the resulting curves could require speed restrictions, don't diverging routes require a speed restriction unless the frog is really shallow?

Any railway engineer worth his salt would have the two main tracks separate very gently (to provide space for the passing track) so trains staying on the main needn't slow down.  Unless high speed turnouts were used for the turnouts leading to/from the siding, speed restrictions only applied to trains taking the siding.

Mark

[Hudson]

jeffhergert

 

Speed restrictions would depend on the size of the turnout, not what type it is. 

 

Just to be clear.........If you have to kick out the two main tracks in order to place a passing track in between the resulting curves could require speed restrictions, don't diverging routes require a speed restriction unless the frog is really shallow?

[jeffhergert]

One territory where I work still has a center siding.  The layout is a Y turnout, or very close to it, at either end with access to both main tracks at both ends.  This is in current of traffic territory and all the switches are hand thrown.  The normal position of the Y turnouts at either end is to allow something leaving the siding to move with the current of traffic. 

Speed restrictions would depend on the size of the turnout, not what type it is.   

Jeff 

[Hudson]

markpierce

It was preferable the center siding only served one mainline.  I presume this was to avoid two-way traffic on a portion of the line where otherwise there was only one-way traffic.

 

To avoid speed restrictions as well.......................If you Y into a center passing track you need to restrict speed on both mains.........sidings for 2 track main are usually on the steeper side of a grade......

 

[markpierce]

I'm looking at some 1930 Southern Pacific track layout diagrams (standard plans) and here are a couple observations.

It was preferable the center siding only served one mainline (edit - I mean main track).  I presume this was to avoid two-way traffic on a portion of the line where otherwise there was only one-way traffic.

Where circumstances required, the plans allowed the center passing to serve both main tracks.  The diagrams show the turnouts on the center siding to be "regular" (only one route is curved, that is, no wye turnouts) with the turnouts coming off the mains offset (not directly opposite) of each other.

Mark

[wjstix]

Yup, I went back and corrected my post.

[Hemifanone]

We did exactly what you propose on our club layout, using three no. 8 turnouts on each end of the siding. No need for a fourth turnout.

 

Graham Hoffman

Plymouth(WI) Model Railroad Club

[wjstix]

If the center track was designed to be used equally by both mainlines, you could do something like this....

Imagine looking from between the two straight mainlines looking down the track towards where the triple-track would start. The main on your left would have a turnout pointing towards the right (towards the middle track) and the track on the right would have a turnout pointing towards the left (again towards where the middle track will be). Then the two are connected via a wye switch. You'd do the reverse at the end of the center track section.

You could do it with four  three regular switches, staggering where the mains joined the center track, but I think using the wye would look better and might work a little smoother.

[wm3798]

 Do you have a track chart showing the interlockings at each end of the siding?  I'm assuming the passing track would have to be able to be accessed from both mains...

Lee

[wmshay06]

Hey folks need some practical input of sorts.  There is a good possibility that I will be able to expand my C&O-based RR to include a double track section that on the prototype included a center passing track.  While I have the track diagrams, it doesn't lend much insight into how to do it from a modelling perspective.  What type of turnounts should be used and would commercial products need to be modified - or are we talking scratch built?  Any thoughts would be helpful.

 thanks
Charles