Geography Reference
In-Depth Information
2.3. Modelling Traffic Flow
In this section, the GIS-based network modelling was used to model the
distribution of traffic flows over the road networks.
First, we calculated the shortest route for commuting travel between each
origin and destination, assigning all trips to the shortest routes possible. All
shortest paths carrying traffic flows were then overlapped with suburb
boundaries, and total commuting flows were summed for each individual
suburb based on the total number of commuters passing through, originating,
and ending in that suburb.
Next, because the spatial unit for suburbs is too coarse to represent the
spatial distribution of the commuting flows, we transformed the total number
of commuting flows from suburbs to 1km by 1km grid cells across the study
area. A
binary dasymetric mapping
method (Langford and Fisher, 1996) was
applied to spatially disaggregate the data. The binary dasymetric method
assumes that the number of travellers is uniformly distributed inside some part
of a suburb (in this case, the grid cells that intersect with the road networks)
and the remaining parts of the zone (non-road areas) necessarily have a zero
commuting flow value.
The maps of spatially disaggregated commuter flows for year 1996 and
2006 are illustrated by Figure 6 (a) and (b). At the regional level, the highest
commuting flows are concentrated in the central Brisbane area, extending
north and south through the transport networks. The 1996 data showed the
commuting flow stretching to the southern areas; and this tendency was found
to be more significant in 2006. The increased commuting flow across the
north-south corridor may have been caused by rapid urban expansion and new
population settlements, especially in the southern suburbs of Brisbane, which
generated increased commuting trips towards Brisbane. A similar pattern of
commuting development was also found in the Gold Coast City area, where
commutes spread considerably towards the north and south areas of the city
along the coast.
A comparison between travel flows between 1996 and 2006 demonstrated
that the central Brisbane area has experienced the highest growth in
commuting flows. This was not only driven by an increase in inbound
commuters but also the increased cross-suburban traffic that passes through
the central Brisbane area. The most significant growth in commuting was
found along the transport corridor between Brisbane and Gold Coast. The
major growth areas along this corridor involves some spatial clustering effect
indicating that in addition to increased commuting interactions towards
