How to write a timetable #1

HEALTH WARNING

Reading this post can seriously affect your sanity. If you are concerned, Spad suggests you wait until How to write a timetable #2 appears, and go straight to the end. Timetable geeks can read on …

Spad’s set himself a challenge. In a few months we’ll get first sight of a future Fishguard timetable. That’s when everyone (Spad included) will queue up to show Arriva/SWWITCH/WAG how wrong they are, what an apology for a timetable, such missed opportunities etc etc. But can Spad do any better, knowing nothing of the black arts of railway timetabling?

The result is here: Spad’s self-help guide to getting from A to B and back to A, five times a day, with a single train, and please everyone with the result. Can it be done, or is it cloud-cuckoo land?

Arriva timetable Spring 2011

Many gaps to fill

FIRST STEPS: ASSUMPTIONS

There are an alarming number to consider. First, what about the existing day and night boat trains? Safest is to assume they stay unchanged, with the same route and timings.

Second, where do the new trains call? It’s not so obvious. If as campaigners hope Fishguard & Goodwick station is quickly reopened, will that also be the terminus for the new trains? Or will there be two Fishguard stops, with extra minutes to allow for in the timetable? And between Fishguard and Carmarthen, will there be stops at Clarbeston Road, Clunderwen and Whitland?

Spad assumes just one stop at the Fishguard end, and calls at all intermediate stops. (That will effectively give them an hourly service east and west. It also suggests it would be better to alternate the schedule through mid-Pembrokeshire so Fishguard and Milford trains occupy alternate hours, rather than bunch in the same hour. That will probably mean timetabling close to Pembroke trains running into Carmarthen – this is getting complicated).

Third, how long is each run, and how long the wait at the terminus? We need minimum time assumptions. Existing timetables give Carmarthen to Whitland in 15 mins, Whitland to Clunderwen in 6, Clunderwen to Clarbeston in 8, Clarbeston to Fishguard in 27, 56 minutes end to end. That seems a safe bet. As for the turnround time at the terminus, Spad has arbitrarily set the fastest turnround at nine minutes. That should be enough,  though a train that’s late coming in is going to ripple its delays through the timetable.

Fourth, what direction should first and last trains go? Spad suspects the first trip should be out of Fishguard eastwards, and the last in the evening a return back to Fishguard.

Fifth, those five daily return trains have to be divided either side of the lunchtime boat train. The choice is between three morning and two afternoon, or two morning and three afternoon/evening. This is tricky. The three morning option gives good daytime coverage, a trip at least every 2.5 hours in each direction. The two morning option reduces frequency to 3 hours or less, but it does give the option of mid-evening trips. Spad opts for the three morning option. The logic is that the night boat train will continue to provide a good late return trip westwards, and it’s more important to establish a regular daytime service for a wide cross-section of travellers. Of course, Spad could be wrong.

Sixth and finally, there’s just one train to do all the work – in fact a single coach Class 153 Super Sprinter, familiar from Heart of Wales and Cardiff Bay lines. How early can it start work, how late can it finish? How long can a crew work, and do crew changes cost more? Spad feels seriously out of his depth here. Better get on with drawing up a timetable, and that way discover if one train can possibly do all the work.

TIME TO TIMETABLE

Now the fun starts. The end-to-end journey time of 56 minutes means there’s no way to set a clockface pattern – a departure at a fixed time every other hour. So it’s a case of making best use of the resources to produce the best results. So five return trips a day, three returns before the lunchtime boat train, and two for the afternoon. When’s the first train out of Fishguard? Let’s try to get people to Carmarthen by 8:30, Swansea by 9:30, Cardiff by 10:30 and London by 12:30. (We could try for earlier, but that would open huge gaps in the morning schedule). Happily there’s a departure from Carmarthen at 8:30 that gives all those connections, ending in Manchester at 14:15. Good start. Fishguard dep 7:24, into Carmarthen 8:20 with ten minutes to spare.

Our shuttle is ready to leave Carmarthen by 8:30, but if it waits a bit longer, there’s an arrival from Newport and Cardiff due in at 8:40. That continues to Pembroke at 8:43, so our Fishguard shuttle can follow it out of Carmarthen at 8:50. (Spad hopes the signalling is up to a train every seven minutes). So with an 8:50 out of Carmarthen, into Fishguard 9:46, the first return is complete, and connections have been made with south-east Wales and as far as London and Manchester. So far so good.

In How to write a timetable Part 2 (coming soon), Spad discovers whether there’s light at the end of the timetabling tunnel, or whether that light is …

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