Gunnislake Line - Tamar Valley Line - ongoing discussion, merged posts

[whole diary]

[grahame]

Wonderful statistics but I live in the real world.

Yeah ... real world micro-example ... 90 minute wait at Trowbridge for a taxi because an infrequent train has been cancelled is far more painful than a 30 minute wait at Exmouth for the next train.

Or this morning at Melksham - single northbound train at 07:53 cancelled, next train 10:02, journey check only offers delay / repay as a "sop".  Still no offer here to use an alternative bus service ...

Further Information

If you hold a valid single, return, or weekly ticket, you will be able to claim compensation for delays of 15 minutes or more. Please keep your ticket and visit GWR^▸ (Great Western Railway).com/DelayRepay

[Ralph Ayres]

Five round trips wiped off the timetable - out of 35 (there are 7 trains on that circuit, running at 30 minute intervals. So average delay to random passengers is 30 minutes / 7 = 4.5 minutes.  A frequent service can withstand it.

Sorry, but I don't think that's a meaningful way of analysing it.  A random passenger has either no delay or a 30 minute one so talking about an average delay is meaningless as no-one is delayed by 4.5 minutes.  As you say, you can prove anything with statistics!

[grahame]

Five round trips wiped off the timetable - out of 35 (there are 7 trains on that circuit, running at 30 minute intervals. So average delay to random passengers is 30 minutes / 7 = 4.5 minutes.  A frequent service can withstand it.

Sorry, but I don't think that's a meaningful way of analysing it.

OK - suggest better alternative please.

A random passenger has either no delay or a 30 minute one so talking about an average delay is meaningless as no-one is delayed by 4.5 minutes.  As you say, you can prove anything with statistics!

Yeah - I should have said "mean" rather than "average".  Definitely the mean - median extra delay if the majority of trains are running is zero.

This is the old "average family has 2.4 children but you'll never find an average family" thing; still (IMHO^▸ (in my humble opinion)) a useful measure in terms of overall planning such as number of school spaces.

[CyclingSid]

old "average family has 2.4 children

That is old, as the average family size is nearer 2.4 persons now.

[grahame]

old "average family has 2.4 children

That is old, as the average family size is nearer 2.4 persons now.

Indeed ...

https://blog.ons.gov.uk/2019/08/02/whatever-happened-to-2-point-4-children/

Now perhaps 1.9 children. Many more people live alone these days, and that's a driver behind the need for house building just as population increase and the need for housing stock renewal ...

[bobm]

Just two round trips wiped off the timetable our of 8 (that's just a quarter or one train) on a line like Swindon-Westbury which runs at intervals of about 2 hours and 15 minutes. Average delay to passengers = 34 minutes. So an infrequent service does wipe out practical use at a far lower number of cancellation - if the average holdup for passenger is one half an hour not less that five minutes, that's darned serious -and it's with less than half the cancellations that Exmouth suffered today.

I must admit I am struggling to get my head around this.  If I go to catch a train I aim to be on the platform a minimum of five minutes before it is due to leave.   However I am not actually delayed until the train is late or cancelled.   That applies to everyone aiming to catch that train.  So even if they arrive at the station 20 minutes before me they will be delayed by the same amount of time as I am if the train is late or cancelled.  No one is delayed by a lesser or greater amount - so I don't understand the validity of the 34 minutes.

[grahame]

Just two round trips wiped off the timetable our of 8 (that's just a quarter or one train) on a line like Swindon-Westbury which runs at intervals of about 2 hours and 15 minutes. Average delay to passengers = 34 minutes. So an infrequent service does wipe out practical use at a far lower number of cancellation - if the average holdup for passenger is one half an hour not less that five minutes, that's darned serious -and it's with less than half the cancellations that Exmouth suffered today.

I must admit I am struggling to get my head around this.  If I go to catch a train I aim to be on the platform a minimum of five minutes before it is due to leave.   However I am not actually delayed until the train is late or cancelled.   That applies to everyone aiming to catch that train.  So even if they arrive at the station 20 minutes before me they will be delayed by the same amount of time as I am if the train is late or cancelled.  No one is delayed by a lesser or greater amount - so I don't understand the validity of the 34 minutes.

It's an interesting one ... here is Melksham to Swindon with 2 trains being cancelled and passenger arriving at the station every 10 minutes.  Of course, in reality on such a thin service they would arrange their timing to arrive for a particular train.

Code:

tats = ["05:33","07:21","07:53","10:02","12:33","14:32","16:41","18:50","20:22"]
tata = ["05:33","07:21","07:53","12:33","14:32","16:41","20:22"]

wt = []
for tat in (tats,tata):
	peeps = 0
	paws = 0
	for hour in range(5,20):
		for min in range(0,60,10):
			popup = hour*60+min
			for service in tat:
				(h,m) = service.split(":")
				goesat = int(h)*60+int(m)
				if goesat > popup:
					paws += goesat - popup
					peeps += 1
					break
	avw = paws/peeps
	print("passengers {} total wait {} minutes - average {:.1f}".format(peeps,paws,avw))
	wt.append(avw)
print ("Extra time waited {:.1f} minutes".format(wt[1]-wt[0]))

passengers 90 total wait 5264 minutes - average 58.5
passengers 90 total wait 8331 minutes - average 92.6
Extra time waited 34.1 minutes

change the first two lines to show 1 in 7 services cancelled on a half hourly pattern (5 in the day)

Code:

tats = ["06:05","06:35","07:05","07:35","08:05","08:35","09:05","09:35","10:05","10:35",
	"11:05","11:35","12:05","12:35","13:05","13:35","14:05","14:35","15:05","15:35",
	"16:05","16:35","17:05","17:35","18:05","18:35","19:05","19:35","20:05","20:35",
	"21:05"]
tata = ["06:05","07:05","07:35","08:05","08:35","09:05","09:35","10:35",
	"11:05","11:35","12:05","12:35","13:05","14:05","14:35","15:05","15:35",
	"16:05","16:35","17:35","18:05","18:35","19:05","19:35","20:05",
	"21:05"]

and you get

passengers 90 total wait 1500 minutes - average 16.7
passengers 90 total wait 1860 minutes - average 20.7
Extra time waited 4.0 minutes

[IndustryInsider]

Let it go, Graham! 

[grahame]

Cancellations to services between Gunnislake and Bere Alston
 
Due to urgent repairs to the track between Gunnislake and Bere Alston all lines are blocked.

Train services running to and from these stations will be cancelled. Disruption is expected until the end of the day.
Customer Advice

Network Rail have identified a sink hole on the tracks of the Gunnislake Branch. Specialist geological technicians are heading to the site to assess the situation, but until then, Gunnislake Branch line services can only operate between Plymouth and Bere Alston where they will terminate and return to Plymouth starting from Bere Alston.

Taxis are in operation between Calstock, Gunnislake and Plymouth.

We apologise for the disruption to your journey today.

[infoman]

This was mentioned on the Spotlight local South West news at 06:25am on wednesday morning

[Pb_devon]

They appeared to have fixed it quite quickly as the 1725 arrival operated that day, plus all subsequent services (per RTT^» (Real Time Trains - website)).

[Jamsdad]

The whole of the Gunnislake is riddled with old mine workings. Speaking strictly and geologically,  they are not sink holes, which is a product of limestone weathering, but can be anything from a major abandoned adit to quite small side shafts. Many were poorly filled, and when they open up they need checking,although only rarely do they cause structural problems. But when they do it's a mess!

[plymothian]

Due to rotting timbers found during an inspection last night, Darkey Lane bridge needs urgent repairs.

The Gunnislake line will be suspended.

The current forecast is that services will operate only as far as Calstock on Saturday 14/09 and the whole of next week.  No service at all on Sunday 15/09.

[Timmer]

Cancellations to services between Plymouth and Gunnislake

Due to urgent repairs to a bridge between Plymouth and Gunnislake the line is closed.

Train services running to and from these stations have been cancelled. Disruption is expected until the end of the day.

Customer Advice
We have been made aware of a bridge in need of repair on our Plymouth to Gunnislake line. Network Rail have deemed it not currently safe to run trains over it. As such, the line is closed while repairs and further inspections are carried out.

Road transport has been requested to provide a regular service in lieu of the train, however at this stage nothing has yet been confirmed. For now, customers boarding at unstaffed stations, please make use of the Help Point to speak with a member of staff for further advice. Devonport, Dockyard, and Keyham stations will continue to be served by our trains running between Plymouth and Penzance.

This is a developing situation, and more information will be provided when we have it.

[a-driver]

Due to rotting timbers found during an inspection last night

Someone needs to be urgently asking how the structure was allowed to end up in such a poor condition.