Approach locking

[ch86]

on a main route is the approach locking 120secs or 180secs?

Cheers

[PJW]

To NR standards it depends on the distance of the signal in rear and also whether the line is for a mixture of freight and passenger, or is only passenger; it can be 120, 180 or 240. The rationale is how long it might take to travel from having passed the previous signal having the expectation that the following signal displaying a proceed aspect and then potentially seeing it at red and being unable to stop. By allowing a long time then we can be sure that if there is a train still approaching then it must be moving at such a low speed that it must be able to stop within the sighting distance of the red.

Note that if the main route is MAR approach released or a platform starter etc than it can be reduced to be 60 sec, since the distance of the signal in rear is not a relevant consideration in these scenarios. Where the timer is set in data then every route from a signal can be given a different time to optimise; where the timer is a physical device, then unless the benefit of rtime reduction is very great then it won't be worth the cost and complexity increase by having more timers, so each route will then adopt the time of the one needing the greatest time value.

Suggest you search for "Time Values" on this website and download the relevant attachment.
However a student should be familiar with whatever practices they choose to adopt for the purposes of undertaking the IRSE exam. In the case of NR then the relevant Railway Group Standards are free to download- although of course there is now far too much to read and assimilate prior to this year's exam.

Don't forget that we disable the website over the weekend of the exam (reflecting not undertaken simultaneously everywhere around the world), so you are running out of time for last minute questions!!

on a main route is the approach locking 120secs or 180secs?

Cheers