Meyer Central Corridor: Sydney geology, infrastructure choke points and the rightful "King"

Sydney topography and infrastructure
Sydney's infrastructure development in many ways is a product of it's geology.  The Central Corridor proposed by Meyer (comprising the Dual CBDs of Parramatta + Sydney and the corridor within the inner west & eastern suburbs surrounding these CBDs) has the highest density of transport infrastructure in Sydney in large part because it is situated on the flat Cumberland plain on which it has been easy to build roads and rail, in the early days of Sydney's growth.  In contrast, the dominant geological feature of Sydney's northern suburbs is the Hornsby plateau, which is a sandstone plateau rising to 200 metres above sea level within the urban area and dissected by steep valleys such as the Lane Cove River valley.  These river valleys are major impediments to construction of transport infrastructure:

Map 1: 8am peak hour Google Maps traffic congestion
Note purple circles showing how Sydney's major river valley barriers and chokepoints lie in the Northern Suburbs

* Middle Harbour divides Northern Beaches centres (Frenchs Forest, Dee Why, Mona Vale) from Kuringgai/Willoughby centres (Chatswood, Gordon).  Connections between these centres is limited to only three choke points, namely Mona Vale road, Warringah road, and The Spit Bridge.  It is no coincidence that these some three of the worst traffic bottlenecks in all of Sydney.
* Lane Cover River divides Kuringgai/Willoughby from Ryde centres such as Macquarie Park.  Again, the limited number of roads connecting these centres also creates major traffic chokepoints: Lane Cove road (A3) at Macquarie Park, Delhi road at North Ryde and Pennant Hills road.  The Lane Cove tunnel is the one exception as it has plenty of spare capacity, but this reflects misjudged (or should I say successful?) toll road pricing.
* Parramatta River of course is the biggest of all these rivers, and divides all northern Sydney suburbs from the central region of Sydney.  Again, limited number of river crossings creates major road choke points: Harbour bridge/tunnel, Devlin St (A3) at Ryde, Iron Cove bridge at Drummoyne and James Ruse drive at Ermington.

In contrast, the centres and major road corridors located within Central Corridor are relatively less congested.  In particular, note Parramatta Rd is mostly green/orange on the above map, reflecting it's relatively less congestion compared to northern road corridors.  The one exception is at Strathfield, where there is a "man made" choke point of the termination of the M4 and the resulting convergence of 10 M4/Parramatta Rd lanes into into 6 lanes.  With the imminent extension of the M4 east, this choke point should be significantly ameliorated, at least until it reaches the Anzac bridge.

It is useful to also note the relatively more dense arterial road network of the inner west suburbs between Strathfield and Sydney CBD.  This partly reflects historical development, but also reflects the flat topography of the inner west allowing extensive transport network construction unimpeded by valleys and rivers.

A similar analysis could be done for Sydney's rail network.  In particular, harbour and river crossings have all proven to be major engineering, environmental and cost challenges, as seen with the multiple aborted attempts at a second harbour crossing and the cost overruns and design changes seen in the ECRL crossing the Lane Cove river.  The fact that the Northern Beaches rail line has often been talked about and studied, but never delivered also reflects these same engineering, cost and environmental challenges.

Northern Sydney employment patterns
These major river barriers between northern suburb centres to a large degree explains why significant clusters of office developments have been built in North Sydney, Chatswood and Macquarie Park - they allow the Northern Suburbs to have a greater degree of "self containment" of employment than the remainder of Sydney.  This self containment is particularly evident in the northern beaches, with 50% of workers working within their residential locality.  In contrast, residents within the inner west corridor actually have very low levels of employment self containment, with only 24% of workers working within their locality, even though the inner west is richer in jobs than the Northern Beaches (82% jobs to resident ratio for Inner west versus 63% for Northern Beaches):

(Note: the "total" bars are better reflections of higher paid, knowledge worker type jobs than the "key workers" bars as the latter reflect less knowledge intense occupations.)

(Note: the above graph shows the richness of job opportunities within each Sydney region.)

Source of both graphs: Northern Beaches Key Workers Study, 2004 by Epic DotGov and Glazebrook Associates.

Western Sydney employment patterns: breaking stereotypes
In fact, even Blacktown, Bankstown, Fairfield and even more distant outer western/southwestern suburbs in Sydney all have a greater tendency to commute outside their region for work compared to the Northern Beaches, with self containment ratios of 30~48% for the former versus 50% for the latter.  The conventional stereotype is that these regions are "jobs poor" and economically deprived regions.  However, the jobs-to-worker ratios for these regions all suggest these regions have similar to superior job opportunities to the Northern Beaches, with the ratios ranging from 74% for Fairfield, 66% for Blacktown, down to 55% for outer south western Sydney, versus 63% for Northern Beaches.

So clearly the data using Northern Beaches as a comparison suggests the stereotype that Sydney's West is jobs-deprived is not entirely correct.  Instead, it suggests that western Sydney residents have a moderate degree of jobs availability locally, but choose still to commute outside their region to work despite this.

Where are they working instead?  The data suggests three jobs-rich regions in Sydney with an excess of jobs - Sydney CBD, Central Western Sydney (ie: Parramatta CBD & surrounding precincts), and lower north shore.  The distances & travel choke points around the latter would make me guess that most western Sydney commuters are going predominantly to Parramatta and Sydney CBD or otherwise working outside these three centres, in the Central Corridor or more widely across Sydney.

Map 2: The Central Corridor proposed by Meyer contains the dual CBDs of Sydney & Parramatta

Why do they do this?  For the very reason that major cities like Sydney exist: centralised job agglomeration benefits make more productive, better paid, more prospective jobs available to the whole city's population, but at the cost of travelling into jobs centres.  The richness and density of the Central Corridor infrastructure is allowing Western Sydney the choice to commute - a choice that the major transport barriers in Northern Sydney denies to Northern Beaches residents.

Employment patterns are a balance of travel cost/capacity versus agglomeration benefits
In summary, the cost of transport/travel outweighs agglomeration benefits of Northern suburbs residents working outside their region, such as in Sydney CBD.  As a result, it could be argued the Northern suburbs have developed their own local employment centres and have higher degrees of employment self containment.  In contrast, it could be argued that centres to the west and southwest, like Penrith and Liverpool have not developed the same degree of employment as Northern Sydney precisely because the Central Corridor has such a density of transport infrastructure it has permitted large numbers of Western Sydney residents to commute outside their region to work in Parramatta and Sydney CBDs.  It could be argued that it is only now with the increasing saturation of the Central Corridor infrastructure, that a partial limit is being placed on this agglomeration and commuting trend, which for the past 50 years has driven the phenomenal growth of Western Sydney.

I use the term "partial limit" because transport bottlenecks are mainly rail/road into Sydney CBD and road into Parramatta CBD.  However, to the extent commuters get off trains at Parramatta, this is actually freeing up inner network capacity, ie it is to a large degree "counterflow" to the main direction of rail commuting.  This is a very effective use of latent capacity and highly desirable, and in my opinion, it is for this reason that Parramatta should be a focus for jobs creation.  In contrast, the "City of Cities" vision for Sydney creates too many centres that dilutes the benefits of agglomeration, as well as diluting the ability of limited transport resources to provide fast, high frequency transit between the large number of centres.

Global Economic Corridor is misconceived
Finally, a lot of people point to the Global Economic Corridor (GEC) as the Sydney-wide employment hub.  This is true of Sydney CBD and the southern half of the GEC, which is also the part of the GEC that overlaps with the Central Corridor.  However, the pervasiveness of transport choke points and river valley barriers dividing up the northern suburbs suggests the northern half of the GEC is really just a regional employment hub for northern Sydney and does not necessarily have Sydney-wide relevance.

The GEC is a "pretender" to the "throne".  The Central Corridor, which incorporates the southern half of the GEC, plus Parramatta CBD and the Parramatta to Olympic Park corridor is the rightful "King" and true Sydney employment hub.