Petone - Managing The Junction

There are many factors that must be taken into account when managing the junction during the morning peak. I describe what the factors are.

I describe a real life (i.e. not hypothetical) example from the morning peak. There are several late and out of order trains and the signalman must decide whether to give a down Melling or a down Taita priority.


48 points switch

These events occurred soon after I had started at Petone. Today, with experience, maybe I would handle things differently. I do not know.





Factors To Be Considered When Managing The Junction

  • Are trains approaching the junction on the Up Main, Down Main, Melling Branch ?
  • Are trains on time or are one or more running late?
  • If a down train is late spotting how late did it leave Taita?
  • Are trains out of order?
  • Are Up train(s) a stopper or an express?
  • Are Down train(s) stoppers; express or Wairarapa?
  • Have Wairarapas been having door problems recently?
  • What is the margin between the arrival of a down Melling and a down train on the main.
  • How crowded is the Petone down platform - best not to put two-car Melling in front of a nine-car red set.
  • When will signals will clear - consider overlaps.
  • Can Down Melling be given the light as soon as it spots - keeps it moving.
Jv set on junction

(Above)   A two-car olive Johnsonville set begins its journey along the 3km Melling branch.




Free Light

When can a junction signal be cleared or points operated?

Free light down Free light up

Down Trains.   The free light on 48 points illuminates as soon as a down service has cleared location F (assuming 14 & 17 signals are at stop). 48 & 47 points can then be operated. If required 14 & 17 signals on the up main can then be cleared. However 77 (on main) or 78 (on branch) signals cannot be re-stroked until the down train has cleared signal 74 and the signals will not clear until the train has passed C.

Rule of thumb margins for changing order and putting down Melling first: Down stopper 4 minutes (although if both trains spot at same time can get Melling out first with stopper getting caution on 74); Down express or Wairarapa 6 minutes.

Blocking Up Main. A train stopping at Petone will hold 74 signal at stop, so a following Melling will come off the branch on a caution indication, blocking the junction. In this situation it may be better to hold the Melling train and put an up train first.

Up Trains.  After an up movement 14 & 17 signals cannot be cleared until the free light on 47 points is illuminated. Note that in order to avoid locking up 48 points or starting a timer (60 seconds) 14 signal is not cleared until the correct route has been set up. i.e. the signalman does not signal an up train to 17 signal and then set up the correct route.

If 14 or 17 signal re-stroked before 47 point free light has illuminated indication lights flash and signal must be restroked.




An Actual Example

It is 0724 during a morning peak in 2007.  Should the Signalman put 4613 or 5617 first?

Petone Junction example

Melling Before 4613

  • 5617 will be in order.
  • 2618 will not be checked.
  • 5617 ready to proceed immediately; 4613 at station stop.
  • Delay to 4613 & 1601.
  • All down trains stop at Petone; if 4613 was an express then it would be better to put it before 5617.
  • 1601 will run on caution signals.
  • If 1601 has the SW cars then could have an extended stop at Petone (doors).
  • Less likely to check 2611.
  • 5618 will not block the up main waiting to enter expressthe branch.

Melling after 4613 & 1601

  • 5617 out of order.
  • 2618 will not be checked.
  • 4613 may not be ready to start immediately.
  • 5617 will be further delayed.
  • No additional delay to 4613 & 1601.
  • 1601 will run on caution signals.
  • If 1601 has the SW cars then could have an extended stop at Petone (doors), further delatying 5617.
  • May check 2611 when getting 5617 out.
  • 5618 may block up the main waiting to enter the branch.



Last Updated: Sun 24th Nov 2013

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