Interworking Services with Different Headways
One of the rules for interworking is that service headways must be compatible. In all previous examples the headways were the same and obviously compatible. In certain circumstances, headways which are not the same can still be compatible, depending on the direct relationship of one headway with the other. The following example will illustrate this point.
Service 6 between Town Centre and Dinmore
Service 7 between Town Centre and Moss Farm.
| Running Times | 27mins Outbound & 28mins Inbound (service 6) |
| 30 minutes in each direction (service 7) | |
| Layovers | 5 minutes at each terminal point |
| Headways | 15 minutes (service 6) |
| 30 minutes (service 7) |
Calculate the number of buses required
Apply the scheduling formula for each service separately
Service 6
27 + 5 + 28 + 5 / 15 = 65 / 15 = 5 buses + 10 minutes
Service 7
30 + 5 + 30 + 5 / 15 = 70 / 15 = 5 buses + 20 minutes
Here is a reminder of the test that will decide if interworking will or will not save a bus:
- if the total excess layover on two or more independently operated services is equal to or greater than the service headways, a bus can be saved by interworking
- headways must be compatible
- there must be at least one common terminal point
There’s no problem in satisfying the third of those conditions – the problem lies with the other two.
It will be seen that the total excess layover time on the two services is 30 minutes, which in this case is greater than the headway on Service No. 7 i.e. the wider headway.
It’s now necessary to determine whether or not the headways are compatible. A comparison of the two headways shows a relationship of 2:1. – in other words, one of the headways divides exactly into the other to give an acceptable ratio.
Other acceptable relationships include headways of:
30 and 10 giving a 3:1 ratio
60 and 30 giving a 2:1 ratio
etc.
Unacceptable relationships include headways of:
20 and 12, 15 and 6, which in neither case gives an exact ratio of one with the other.
Returning to this exercise, the ratio of 2:1 means that for every one departure on Service No 7, there are two on Service No 6. It could also be said that Service No 6 is made of up two 30 minute headways i.e.
Service 6(1) departs Town Centre at 0700, 0730, 0800, etc
Service 6(2) departs Town Centre at 0715, 0745, 0815, etc
By making that assumption, it could be said that instead of looking at the interworking of two separate services, the solution is to look at three separate services – i.e.
a 30 minute headway on Service 6(1)
a 30 minute headway on Service 6(2)
a 30 minutes headway on Service 7
The criteria for interworking have now been met with the following modification:
- if the total excess layover on two or more independently operated services which have a different headway is equal to or greater than the wider of the two service headways, a bus can be saved by interworking
- headways must be compatible in terms of an absolute relationship of one with the other
- there must be at least one common terminal point
Total excess layover in this case is equal to the wider of the two headways.
Calculate the number of buses for interworking
The scheduling formula is modified to look like this:
65 + 70 + 65 / 30 = 200 / 30 = 7 buses + 10 minutes
Working Timetable
| Bus No | 1 | 2 | 3 | 4 | 5 | 6 | 2 | 7 | 4 | 1 |
| Service No | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 |
| Town Centre | 0700 | 0715 | 0730 | 0745 | 0800 | 0815 | 0830 | 0845 | 0900 | 0915 |
| Dinmore | 0727 | 0742 | 0757 | 0812 | 0827 | 0842 | 0857 | 0912 | 0927 | 0942 |
| Dinmore | 0732 | 0747 | 0802 | 0817 | 0832 | 0847 | 0902 | 0917 | 0932 | 0947 |
| Town Centre | 0800 | 0815 | 0830 | 0845 | 0900 | 0915 | 0930 | 0945 | 1000 | 1015 |
| Service No | 7 | 7 | 7 | 7 | 7 | |||||
| Town Centre | 0805 | 0835 | 0905 | 0935 | 1005 | |||||
| Moss Farm | 0833 | 0903 | 0933 | 1003 | 1033 | |||||
| Moss Farm | 0838 | 0908 | 0938 | 1008 | 1038 | |||||
| Town Centre | 0905 | 0935 | 1005 | 1035 | 1105 |
Note that bus number 2, for example, after arriving Town Centre at 0815 takes 15 minutes layover (5 minutes minimum and 10 excess) before its next departure at 0830, a pattern which is shared by all other journeys that are not followed by a journey to Moss Farm.
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