I found this interesting paragraph in a journal article referenced below (no link, sorry).
Conversely, the relatively poor average closeness centrality scores in Zuid Holland, the Australian and US cities are linked to the relatively wide spacing of places of activity. In Zuid Holland this relates to the conurbation’s multi-nuclear form without a single overarching center. In Australia and the United States, places of activity tend to be separated by expanses of low-density suburban fabric, usually lacking in high-speed public transport infrastructure that could make up for the spatial discontinuity. Perth is the Australian exception where the principal public transport spine (the fastest suburban rail service in the sample cities) is optimized for the specific conditions of a low-density city with relatively weak sub-centers.
This study, which analysed public transport accessibility in 20 large global cities, considered "closeness centrality" as a measure of the impacts of service frequency and travel time between any two given points on the network. The Suburban Rail Loop, I suspect, has the potential to radically improve Melbourne's score on this front in a manner which improved orbital bus networks would fail to match. Another initiative that has been discussed in this thread which would help this score is the RFI's south-east fast line proposal.
Otherwise, among the Australasian and North American sample, only Sydney has more than half of all residents and jobs within walking distance of public transport at the SNAMUTS standard. This reflects Sydney’s longstanding policy of urban intensification around rail stations, higher settlement density, and greater constraints to outer suburban expansion compared to its regional peers.
The SRL's expected benefits to suburban employment clusters will only
materialise if government policy actively encourages development near the new stations and actively discourages employment centres developing elsewhere.
The global betweenness indicator benchmarks the attractiveness of the public transport system as a whole to facilitate movement and accessibility across a case study city, allowing for comparison between cities. It is affected by the urban compactness and contiguity bias seen in the network coverage indicator. The catchment size of a typical journey path measure, designed to compensate for this bias, determines the number of residents and jobs traveled past on a public transport journey of average length in the respective metropolitan area. This figure is influenced by the concentration of activities in each nodal catchment area as well as the propensity of the network to attract passengers (or not) along geographical detours that may lengthen the journey but offer shorter travel times and better service frequencies.
Zuid Holland, Melbourne, and Zurich occupy an intermediate position. For Zuid Holland and Melbourne as relatively large cities, this could be read as a lower-than -expected performance; however unsurprisingly, since this indicator strongly rewards compact, dense, and contiguously urbanized settlement areas and penalizes spatial discontinuities, regardless of whether they are generated by topographical constraints or result from policy decisions or historical trends.
In such cases, the network configuration tends to encourage longer-than-necessary trips (in terms of geographical distance and by extension, number of other activity centers passed along the way). At the lower end of the scale, Melbourne’s and Zuid Holland’s similar results may be attributed to the incidence of “missing links” between neighboring activity centers.
In other words, the benefits generated by the SRL will almost certainly massively contribute to the overall attractiveness of public transport and substantially improve Melbourne's global standing in the provision of suburban services, in a way that incremental upgrades to the existing network simply cannot.
For those who've been questioning the reasons for my total support for this project, this is why: it reflects in near-totality the current state of transport planning theory and will make a generational difference to the way we think about public transport.
Ref: Curtis, Carey, and Jan Scheurer. "Performance Measures for Public Transport Accessibility: Learning from International Practice." Journal of Transport and Land Use
10, no. 1 (2017): 93-118.