Frequency Change
In this exercise Service No. 3 from Town Centre to Granary will be used to illustrate the mechanics of increasing and decreasing frequencies.
| Running Time: | 20 minutes each way |
| Minimum Layover: | 2 minutes at each terminal point |
| Headway: | 10 minutes (Peak Hours) |
| 12 minutes (Between Peaks) | |
| 15 minutes (Evenings) |
For the purpose of the exercise a section of the full timetable will be examined covering a period from 1500 to 1900
The Peak hour for this timetable is between 1600 and 1730 from the Town Centre, and between 1622 and 1722 from Granary.
Calculate the number of buses required apply the scheduling formula for each headway separately
Peak times
20 + 20 + 2 + 2 / 10 = 44 / 10 = 5 Buses + 6 minutes
It can be seen that the headway, 10 minutes, does not divide exactly into round journey time, which is 44 minutes. In other words, the round journey time is NOT a multiple of the headway.
It isn’t possible to have fractions of buses, and so the solution is to increase the round journey time (44) to make it into a multiple of the headway. The next multiple of 10 above 44 is 50. The round journey time is increased by adding additional layover which is called EXCESS LAYOVER
Between the peaks
44 / 12 = 4 Buses + 4 minutes
The same problem arises again. The round journey time (44) has to be increased again to make it into a multiple of the headway. The next multiple of 12 above 44 is 48.
Evening
44 / 15 = 3 Buses + 1 minute
On this occasion the round journey time (44) has to be increased again to make it into a multiple of 15 which is 1 extra minute to make it 45.
The Working Timetable
| Bus No | 1 | 2 | 3 | 4 | 1 | 2 | 3 | 4 | 5 | 1 | 2 | 3 | 4 | 5 | 1 | 3 | 4 | 1 | 3 | 4 | |
| Town Centre | 1500 | 1512 | 1524 | 1536 | 1548 | 1600 | 1610 | 1620 | 1630 | 1640 | 1650 | 1700 | 1710 | 1720 | 1730 | 1745 | 1800 | 1815 | 1830 | 1845 | |
| Granary | 1520 | 1532 | 1544 | 1556 | 1608 | 1620 | 1630 | 1640 | 1650 | 1700 | 1710 | 1720 | 1730 | 1740 | 1750 | 1805 | 1820 | 1835 | 1850 | 1905 | |
| etc. | |||||||||||||||||||||
| Granary | 1522 | 1534 | 1546 | 1558 | 1610 | 1622 | 1632 | 1642 | 1652 | 1702 | 1712 | 1722 | 1737 | – | 1752 | 1807 | 1822 | 1837 | 1852 | 1907 | |
| Town Centre | 1542 | 1554 | 1606 | 1618 | 1630 | 1642 | 1652 | 1702 | 1712 | 1722 | 1732 | 1742 | 1757 | – | 1812 | 1827 | 1842 | 1857 | 1912 | 1927 |
Note
Bus number 5 is introduced into the timetable at 1630 Town Centre
Bus number 4 holds back an extra 5 minutes from 1732 to 1737 at Granary because in this example a change in frequency is introduced at the Granary at 1722
2 buses are released to return to Garage
number 2 from Town Centre at 1732
number 5 from Granary at 1740
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