Section 4 : More Interworking and The Peaks

Impact of the peaks

It’s important to minimise the number of buses in service at all times. In the peak, however, it is even more crucial that the number of buses employed is kept to a minimum and extra buses are not drafted into service. The peak is the time at which the maximum number of buses is already in service so introducing an extra vehicle means that the operator needs to increase the fleet size with all the associated costs of ownership.

Definition of the vehicle peak

The vehicle peak can be defined as:

the time between the last bus leaving garage and the first bus returning to garage

A problem is the vehicle peak also coincides with peak movement of people and other road traffic. Delays often occur to buses and extra running time is sometimes needed because of general traffic congestion and the resulting delays to service.

One solution is to increase running times at the peak periods.  Another is to be selective in resolving problems of late running by introducing ‘drop-backs’ after the vehicle peak.

In this exercise a problem of late running in the evening peak between 1600 and 1700 hours will be looked at, using the timetable of Service No. 12 which operates from the Town Centre to Moreton.

Bus No.	1	2	3	1	2	3	1	2	3
Town Centre	1600	1610	1620	1630	1640	1650	1700	1710	1720
Moreton	1613	1623	1633	1643	1653	1703	1713	1723	1733
Moreton	1615	1625	1635	1645	1655	1705	1715	1725	1735
Town Centre	1628	1638	1648	1658	1708	1718	1728	1738	1748

In practice, Bus No 1 is seldom back in the Town Centre to leave again at 1630, with subsequent journeys having similar delays.

Inserting a Drop-back

Let it be assumed that the vehicle peak for all services is as follows:

last bus leaves garage at 1555 first bus returns to garage at 1632

It can be seen that a bus returning to the garage will be in the Town Centre at 1627. Instead of returning to garage, this bus (No. 4) can be slotted in to run the 1630 journey from Town Centre to Moreton.  This allows a series of ‘Drop-backs’ to take place as the following working timetable shows.

Bus No.	1	2	3	(1)4	(2)1	(3)2	(1)3	(2)1	(3)2
Town Centre	1600	1610	1620	1630	1640	1650	1700	1710	1720
Moreton	1613	1623	1633	1643	1653	1703	1713	1723	1733
Moreton	1615	1625	1635	1645	1655	1705	1715	1725	1735
Town Centre	1628	1638	1648	1658	1708	1718	1728	1738	1748

Bus number 4 is introduced at 1630 for one trip so enabling all other buses to drop back 10 minutes as follows:

                          bus No. 1 leaves at 1640 instead of 1630

                          bus No. 2 leaves at 1650 instead of 1640

                          bus No. 3 leaves at 1700 instead of 1650

Bus number 4 could in fact operate longer to provide recovery time for a greater period.

The only cost is the time element due to the later return of bus No. 4 to garage.  If an extra bus had been introduced before 1630,  an additional vehicle would be needed. There is no vehicle cost yet the problem of late running has been solved by increasing specific round journey time instead of increasing  general running time.