In many urban areas the central area is surrounded by lower density suburbs and a decision must be made about whether to operate services across the city centre, or to have a series of simple radial routes terminating in the centre. There are advantages and disadvantages to both (see Table 4.3), and it is likely that an optimum network will comprise a mixture of simple radial and cross city services.
|Simple Radial Services||Cross City Services|
|Provides fewer direct travel opportunities
Provides more flexibility to tailor frequency of service and bus capacity in response to demand
Requires more terminal space in the central area which might be difficult to obtain
Can improve operational reliability as delays through the central area can be mitigated by providing for recovery time at the central terminal
Journeys which start or terminate in the CBD will be involved in either picking up or setting down, not both
|Offers more direct travel opportunities
Can result in inefficient operations if the demand either side of the centre is uneven
Does not require central area terminal space
Operational reliability can be adversely affected by delays through the central area.
Improves resource utilisation – as buses travel through the CBD they are both picking up and setting down passengers
Table 2; Comparison of Radial and Cross City Services
Care must be taken that cross-links are sensible, and offer genuine benefits. For example, a service which has to pass through the whole breadth of the CBD may prove to be unreliable due to the volume of congestion encountered, or the overall route length may prove too long to feasibly operate. The following check list offers a guide to sensible cross-linking; the route pattern should:
- cater for any existing / potential cross-town demand between specific Origin-Destination pairs;
- provide as many people as possible with a link to as much of the CBD as possible;
- equalise demand on the two ends so as to enable operation of optimum headways;
- have sensible, “marketable” routing in the town centre, providing common stops for common corridors;
- put together services so as to get a total cycle time that fits with desired headways so as to minimise wasted time; and
- balance each of the above to achieve the most attractive network in the specific scenario.