The widening of the 7.5 kilometres (4.7 mi) M4 section east of Church Street, Parramatta, began construction in March 2015 and was completed in July 2017.

Stage 2 works included upgrading the existing M5 interchange at King Georges Road, and building the new M8 Motorway,[17] a new set of tunnels between the M5 at Beverly Hills and St Peters.

Though construction of the roads progressed slowly – by 1971 only isolated sections were complete – the Plan ensured corridors were reserved, providing property owners with certainty about future infrastructure.

[citation needed] Though Wran's decision to sell off the M4 East corridor was later criticised,[37] the Cumberland Plan's radial concept was anyway beginning to lose relevance.

The city's passenger and freight gateway had shifted 14 kilometres (8.7 mi) south of the CBD, with long-distance passengers increasingly arriving via Sydney Airport, not Circular Quay or Central station; and Port Botany increasingly supplanting Sydney Harbour as the city's main shipping hub.

After last-minute revisions to the design, the resulting motorway, opened in 2001, was too steep for laden trucks returning from Port Botany, significantly increasing vehicle emissions and frequently overwhelming the ventilation system.

In March 2007, prior to the state election later that month, The Daily Telegraph claimed the government was planning the Inner West Motorway, which was similar to the Marrickville Tunnel.

It would be a tunnel which would run from St Peters underneath Enmore, Stanmore, Camperdown and Annandale to City West Link and Victoria Road.

Feedback received was used to further develop and refine the scheme to become the King Georges Road Interchange Upgrade and New M5 projects of the WestConnex.

The initial scheme called for:[54] The tunnel from the M4 to St Peters component would provide the first step towards an inner-city bypass, which was originally planned to connect the airport to the Victoria Road corridor.

This proved a stumbling block in securing federal funding for the project, despite the risk of a motorway direct to the city competing with existing public transport services.

[64] However, the Business Case and list of objectives were written retrospectively, long after state and federal funding for the project was announced.

Infrastructure Australia criticised the NSW Government for not adequately appraising alternative ways of meeting the project objectives.

[70] For example, road freight productivity could be improved, and congestion reduced, simply by tolling the existing M4 and M5 motorways, which is being done anyway to cross-subsidise to the new tunnels.

[71] WestConnex was supported by the state and the federal Liberal Party governments, including former Premier Gladys Berejiklian[8] and former Prime Minister Malcolm Turnbull.

WestConnex also received support from multiple third party organisations, such as the motoring lobby group the NRMA, which argued that it would help improve transport in Sydney's west,[74] significantly reduce travel times and complete a plan from 1947.

[78] Lucy Turnbull, the chief commissioner of the Greater Sydney Commission and wife of former Prime Minister Malcolm Turnbull, voiced her support for the project albeit with concerns for the preservation of heritage sites in Haberfield, stating that the development needs to "strike the right balance between protecting our homes and heritage and building a Greater Sydney that will work well for future generations".

[92] The impact of the project on public transport continued to be a matter of concern into 2016 with "no detail on what sort of public transport will be included on the road surface"[93] and repeatedly expressed concerns that experience with motorways shows they generate traffic and increase congestion[13] and that Westconnex will similarly add to congestion, rather than relieving it.

[94] The planning and approval process for Stage 1A of the scheme (widening the M4) was criticised by Grant Hehir, the NSW Auditor-General, for failing to abide by the Government's own assurance arrangements for major projects.

[98] The government, although "urged" to consider the fairness of the process of compulsory acquisition for the land required for the project and act on recommendations in a legal report to improve it, decided to take "no further action".

[101] Protests have been strong against the felling of mature heritage trees in preparation for "the 40-hectare spaghetti interchange – as big as Sydney Park itself".

[94][102][103] In January 2016, the Wolli Creek Preservation Society raised concerns that complying offsets are unlikely to be available for the irreparable damage to the Beverly Grove bushland from the temporary use of 1.4 hectares (3.5 acres) as a construction compound.

[104] On 11 July 2016, the Second Turnbull Ministry announced the environmental approval for Stage 2 of the WestConnex motorway with a captive breeding plan and construction and maintenance of additional habitat for the green and golden bell frog and offsets for damage to the critically endangered CCRIF.

[105][106] The destruction of heritage properties in Haberfield, a suburb listed in its entirety as a Conservation area, has been the subject of specific criticism, especially when the chair of the Greater Sydney Commission said she was unaware of it.

[107][108] The compulsorily acquisition of residential properties in inner-city suburbs for the project, including "at least 50 listed heritage buildings"[13][109] has been the subject of much criticism and opposition on grounds of disruption, loss of heritage and unfairness of process, including the Government's decision to release only the executive summary of the project's business case.

[111] A proposal in 2016 for an additional tunnel between Iron Cove Bridge and an interchange at Rozelle, required the acquisition of further residential properties.

Residents whose homes were affected reportedly received letters about such acquisitions on the same day that the responsible Government Minister said final decisions on them "had yet to be made".

[131] According to a report commissioned by the City of Sydney, once excluded factors are properly considered, the full cost of the project may be more than $45 billion.

[64] On 12 May 2017, the NSW Government announced its intention to sell at least 51% of Sydney Motorway Corporation, the holding company for the WestConnex project.

In 2014, the NSW Auditor-General, Grant Hehir at the time, conducted a performance assurance audit covering the period from the development of the concept in October 2012 through to the pre-tender phase for Stage 1 in March 2014 and concluded that:[141] In the period covered by this audit, the processes applied to WestConnex to provide independent assurance to [NSW] Government did not meet best practice standards.