Look at the following route network:
Service No. 10 operates between Town Centre and Long Green via Gilmore
Service No. 11 operates between Town Centre and Hillbury via Gilmore
| Running Times | 28mins Outbound & 27mins Inbound (service 10) |
| 15 minutes in each direction (service 11) | |
| Town Centre to Gilmore 10 minutes in each direction | |
| Layovers | 5 minutes at each terminal point |
| Headways | 15 minutes on each service |
Services 10 and 11 should be timed, therefore, to provide a common headway of 7½ minutes (7/8) between Town Centre and Gilmore.
Calculate the number of buses required
Service No. 10
28 + 5 + 27 + 5 / 15 = 65 / 15 = 5 buses + 10 minutes
Service No. 11
15 + 5 + 15 + 5 / 15 = 40 / 15 = 3 buses + 5 minutes
A bus can be saved by interworking because the total excess layover above (15 minutes) is equal to the headway. The final decision on saving a bus is going to be put on one side until a decision is made on inter-timing.
Test to see if exact inter-timing is possible
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
Layover at the common terminus is now 10 minutes for the two services (5 minimum + 5 excess). The 5 minutes excess layover that were taken away from the layover of service 10 at the common terminus are now added or reassigned to the minimum layover at the outer terminus of service 10.
Increasing the layover at the outer terminus of service 10 has the effect of holding back departures from Long Green by an extra 5 minutes which means that buses on services 10 and 11 pass Gilmore, the common mid route timing point, at exact 7½ (8/7) minute intervals. In effect the round journey time of service 10 is increased from 65 minutes to 70 minutes.
Note that the time difference between the two round journey times is a multiple of the headway – this has to be the case for inter-timing to be achieved.
Working Timetable – inter-timing with no interworking
The best possible timetable giving exact inter-timing of 7½ minutes (8/7) between Town Centre and Gilmore using 8 buses will look like this:
| Bus No. | 1 | 6 | 2 | 7 | 3 | 8 | 4 | 6 | 5 | 7 | 1 |
| Service No | 10 | 11 | 10 | 11 | 10 | 11 | 10 | 11 | 10 | 11 | 10 |
| Long Green | 0623 | .. | 0638 | .. | 0653 | .. | 0708 | .. | 0723 | .. | 0738 |
| Hillbury | .. | 0643 | .. | 0658 | .. | 0713 | .. | 0728 | .. | 0743 | .. |
| Gilmore | 0640 | 0648 | 0655 | 0703 | 0710 | 0718 | 0725 | 0733 | 0740 | 0748 | 0755 |
| Town Centre | 0650 | 0658 | 0705 | 0713 | 0720 | 0728 | 0735 | 0743 | 0750 | 0758 | 0805 |
| Service No | 10 | 11 | 10 | 11 | 10 | 11 | 10 | 11 | 10 | 11 | 10 |
| Town Centre | 0700 | 0708 | 0715 | 0723 | 0730 | 0738 | 0745 | 0753 | 0800 | 0808 | 0815 |
| Gilmore | 0710 | 0718 | 0725 | 0733 | 0740 | 0748 | 0755 | 0803 | 0810 | 0818 | 0825 |
| Hillbury | .. | 0723 | .. | 0738 | .. | 0753 | .. | 0808 | .. | 0823 | .. |
| Long Green | 0728 | .. | 0743 | .. | 0758 | .. | 0813 | .. | 0828 | .. | 0843 |
Is it still possible to save a bus by interworking?
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