Changes in activity distribution

In order to test the sensitivity of the methodology to changes in the spatial distribution of activities, the Christchurch-based meshblock calculations were re-run, with a hypothetical new hospital added on the rural fringe of Halswell (on rural zoned land on Halswell Junction Road, opposite the T-junction with Nicholls Road).

The four results for each transportation mode for the hospital activity are presented in figure 16.3 and the impact this has on the final accessibility result is presented in figure 16.4. The full results of the model run are presented in appendix F2.

Fig 5_3

Figure 16.3   Modelled change in accessibility (aggregated accessibility score) to hospitals by transportation mode, for a new hospital in western Halswell


From figure 16.3 the sensitivity of the model to a new land use can be discerned. As would be expected, the impact on walking accessibility is only experienced close to the location of the change (Halswell). Access by cycling shows a radial distribution from the site of the new hospital with the strongest positive change in cycle accessibility closest to the new hospital. This is to be expected as the area around Halswell is flat and a constant cycling speed of 20km/h is assumed on flat terrain. Private vehicle accessibility also shows a radial pattern of impact with the greatest effect along arterial transportation routes that provide fast vehicle speeds.

The largest magnitude of change >0.80 is found in the walking network around Halswell as this region previously had no walking access to a hospital. More muted improvements in the aggregated accessibility score (0.4–0.6) are found for the other modes of transportation as some level of accessibility to hospitals was already realisable in this area before the addition of the new hospital.

Given the public transportation network models journeys starting on the walking network before transferring to the bus, the maximum accessibility gain is similar to that of the walking network, where the meshblock centroids closest to the modelled location of the new hospital show the greatest gain. As expected there is an obvious ridge of improved accessibility levels aligned along the bus routes between Halswell and the central city (figure 16.3).


Fig 5_4
Figure 16.4   Modelled impact of a new hospital in western Halswell on the overall accessibility to the consumed comprehensive accessibility score


The magnitude of the average impact of the modelled change on the comprehensive accessibility score is less pronounced (positive, but < 0.20). This is to be expected as hospitals are only one of the seven activity types which are measured to arrive at the final score.

The inclusion of a new hospital shows the greatest improvement in accessibility score (+0.64) for the 0–4 years age group and the 65 years and over age group (+0.69). This is a reflection of the increased significance of hospitals (relative to other activity types) selected for these age groups. This increased significance was modelled using the weighting matrix (appendix E) that weights the relative significance of each activity type to the various age groups.