Orbital network: "spider-web" versus "grid"

Sydney's key economic corridors follow an orbital pattern, and it's rail network has a "spider-web" organisation.  The diagram below looks at an example comparison of travel distances for the spider-web type of network versus a grid based network:

So some conclusions from the example above are that where the orbitals are elliptical, with a stretched out east-west axis then east-west travel times along the orbits are very competitive with the more "direct" grid network route.  However, travel along the short axis (ie: north-south axis) can be quite uncompetitive.  For this reason, the spokes of the spider web network should focus on north-south connectivity.

Greater Sydney's rail network (as planned for 2024, plus reserved corridors - see below) is an excellent example of these principles:

Furthermore, the above considerations explain why the extension of Sydney metro to Liverpool via Bankstown airport is so effective.  As shown in the calculations above, a route along the southwest orbital of an ellipse is shorter than a route using the long axis of the ellipse.  The above theoretical calculations is confirmed in practice, as seen in the following distance measurements and comparisons:

At present, for the South line via Granville route:

1. Liverpool to Central via Granville = 34.5km

2. Cabramatta to Central via Granville = 31.5km

3. Off peak frequency 3~4tph, ie: every 15-20mins

4. Acceleration & dwell times: slow

If Sydney Metro is extended to Liverpool & takes over Cumberland line/South line (see rail network diagram below):

1. Liverpool to Central via Bankstown airport = 27.6km

2. Cabramatta to Central via Liverpool & Bankstown airport = 30.6km

3. Offpeak frequency will have <6min headways

4. Acceleration & dwell times: fast

Note on relative patronage: Cabramatta to Liverpool section has daily 19500pax, the section north of Cabramatta to Guildford only has 14500pax.

This means Bankstown airport is shorter route for Cabramatta and any stations south of Cabramatta. For Liverpool, it is 6km shorter. The relative patronage of these stations means the "winners" (who travel a reduced distance) outnumber the "losers" (who travel greater distances). However, even the "losers" really are winners once the 12min reduction in wait times and faster acceleration/dwell times are factored in.

Virtually everyone on South line wins if it is connected to Sydney Metro Southwest via an extension to Liverpool through Bankstown airport, as shown in this rail diagram: