Section 3 : Inter-timing Services

Is it still possible to save a bus by interworking?

Let’s take another look at the calculation that was arrived at after having adjusted excess layovers to achieve inter-timing:

Service No. 10

28 + (5+5) + 27 + 5 / 15 = 70 / 15 = 5 buses + 5 minutes

Service No. 11

15 + 5 + 15 + 5 / 15 = 40 / 15 = 3 buses + 5 minutes

Now that 5 of the original 15 minutes excess layover have been added to the minimum layover at Long Green, only 10 excess minutes remain and so, if the revised calculation is applied, interworking will not save a bus because 15 or more excess minutes are needed.

Saving a bus will therefore mean sacrificing exact inter-timing.  So, if a bus IS saved, what will the combined timetable for the two services be like?

If the two services are interworked, it must follow that a bus will operate a round journey on service 10 followed by a round journey on service 11. 

If a bus leaves, say, at 0700 on service 10, applying the known  round journey time of  65 minutes would mean that the next journey on service 11 operated by this bus is at 0805 (65 minutes later).  It can be concluded therefore, that if headways of 15 minutes are operated on the two services, departures past each hour from the common terminus will be as follows:

               Service 10            00, 15, 30, 45

               Service 11             05, 20, 35, 50

So instead of a straight 7½ (8/7) headway over the common portion of route, the split will be 5/10. A very simple rule emerges.

The individual excess layovers are 10 on service 10, and 5 on service 11.  Interworking takes out this excess layover, but these figures give the clue as to what the split will be other than a straight 7½ (8/7) headway over the common portion of route – it will be 10 and 5 which coincides with the two excess layovers.   But for this to be true, the layover at the common terminus must be the same on the two services, and the total excess layover must be equal to the headway.

Working Timetable – interworking with no inter-timing

The best possible timetable to give interworking with 7 buses will look like this with gaps of 10 and 5 minutes over the common portion of route:

Bus No.        1234562741
Service No11101110111011101110
Long Green..0633..0648 0703..0718..0733
Hillbury    0640..0655..0710..0725..0740..
Gilmore     064506500700070507150720073007350745 0750
Town Centre065507000710071507250730074007450755 0800
           
Service No10111011101110111011
Town Centre0700070507150720073007350745075008000805
Gilmore   071007150725073007400745075508000810 0815
Hillbury..0720..0735..0750..0805..0820
Long Green0728..0743..0758..0813..0828 

Conclusions

There are two options:

  • achieve exact inter-timing  over the common portion of route with a 7½ (8/7) headway using 8 buses
  • reduce the number of buses from 8 to 7 by interworking which means giving up the opportunity to achieve exact inter-timing over the common portion of route

On this occasion it isn’t possible to save a bus and at the same time achieve exact inter-timing.

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