Suburban Rail Loop
The Suburban Rail Loop (SRL) is a planned 90-kilometre orbital heavy rail line designed to encircle Melbourne's middle suburbs, interconnecting the city's existing radial rail lines from Frankston in the southeast to Werribee in the west while providing a direct link to Melbourne Airport.[1] Announced in 2018 by then-Premier Daniel Andrews as a signature infrastructure initiative of the Victorian Labor government, the project aims to alleviate congestion on radial routes, support urban densification in suburban centers, and reduce reliance on car travel by enabling orbital connectivity without passing through the central business district.[2] Construction has commenced on the initial SRL East stage, a 26-kilometre twin-tunnel segment with six underground stations linking Cheltenham and Box Hill, with early works underway since 2022 and full tunnel boring scheduled to begin in 2026, targeting passenger services by 2035.[2] The Victorian government estimates SRL East construction costs at $30 to $34.5 billion, funded in part by $2.2 billion from the federal government, though independent analyses project total lifecycle expenses for East and subsequent North stages exceeding $216 billion when including operations and maintenance to 2084.[3][4] The project has sparked significant controversy amid Victoria's escalating state debt, with critics questioning its benefit-cost ratio, potential for cost overruns, and opportunity costs relative to alternative transport investments, as highlighted in evaluations by Infrastructure Australia and parliamentary budget analyses that underscore uncertainties in long-term projections and scope risks.[5][4] Despite commitments from the current Allan administration to proceed, opposition parties have advocated for scaled-back implementation contingent on fiscal reviews, reflecting broader debates on the sustainability of large-scale public works in a high-debt environment.[6][7]Project Overview
Route and Technical Design
The Suburban Rail Loop (SRL) comprises a 90-kilometre orbital railway designed to encircle Melbourne's middle-ring suburbs, interconnecting existing radial lines from the Frankston Line in the southeast to the Werribee Line in the west via Melbourne Airport in the northwest.[8][1] This ring configuration bypasses the central business district, enabling direct suburb-to-suburb travel and integration with major employment, education, and transport hubs.[1] Construction is phased, beginning with SRL East, a 26-kilometre twin-tunnel segment linking Cheltenham station on the Frankston Line to Box Hill station on the Lilydale and Belgrave lines.[9] This initial phase includes six new underground stations at Cheltenham, Clayton (a major interchange with the Cranbourne, Pakenham, and Frankston lines), Monash University, Glen Waverley, Mount Waverley, and Box Hill.[10] Subsequent phases, SRL North and SRL West, will extend the loop northward through areas including Broadmeadows and the airport, and westward to complete the circuit, incorporating additional stations and super-hubs at locations such as Clayton, Broadmeadows, and Sunshine.[1] Technically, the SRL employs metro-style rapid transit technology, with SRL East and North sections featuring fully automated, driverless operations using state-of-the-art signalling systems on a standalone network independent of the existing metropolitan rail infrastructure.[4][11] Trains will consist of new four-car automated units optimized for high capacity, low noise, and accessibility, supported by twin bored tunnels averaging 26 metres in depth for SRL East, excavated using tunnel boring machines (TBMs) commencing in 2026.[12][13] The design prioritizes seamless integration with surface transport via multi-modal precincts, while cross passages in the tunnels ensure safety and maintenance access.[14]Stated Objectives and Expected Benefits
The Suburban Rail Loop (SRL), as outlined by the Victorian Government, seeks to establish a 90-kilometre orbital railway line linking major Melbourne metropolitan lines from Frankston to Werribee via Melbourne Airport, functioning as both a transport infrastructure and urban planning initiative to interconnect suburbs and redirect population growth away from outer fringes toward established middle-ring areas.[15][8] The core objectives include easing pressure on existing radial rail networks, facilitating direct inter-suburban journeys without reliance on the central business district, and integrating new stations with precinct developments to enhance access to employment, education, healthcare, and services.[16][1] Anticipated transport benefits encompass substantial reductions in journey times, such as 35 minutes from Burwood to Melbourne Airport and 10 minutes from Box Hill to Monash University, supported by turn-up-and-go frequencies of trains every two minutes in peak periods across the initial eastern section's six underground stations (Cheltenham, Clayton, Monash, Glen Waverley, Burwood, and Box Hill).[15] Three designated transport superhubs at Clayton, Broadmeadows, and Sunshine are planned to improve interchange with regional rail, V/Line services, and high-speed options, thereby decreasing overall road congestion and car dependency.[16][8] Projected economic and urban outcomes include the creation of up to 24,000 construction jobs, with 8,000 directly tied to SRL East and at least 10% allocated to apprentices, trainees, or cadets, alongside the enablement of over 70,000 new homes and 230,000 jobs in station precincts through mid-rise developments and value capture mechanisms.[15][16] These developments are expected to incorporate affordable housing provisions, expanded community services like schools, and environmental mitigations such as planting more than 4,000 new trees to offset impacts, ultimately aiming to bolster Victoria's gross state product via agglomeration effects and long-term productivity gains.[15]Historical Context and Development
Pre-Proposal Background
Melbourne's suburban rail network originated in the late 19th century as a radial system converging on the central business district (CBD), with the first suburban lines opening in the 1880s and electrification commencing in the early 20th century to serve growing outer areas.[17] This structure prioritized spokes radiating from Flinders Street Station, reflecting the era's focus on CBD-centric commuting patterns, and expanded through the interwar period without significant orbital connections.[17] By the mid-20th century, post-war population growth and urban sprawl amplified cross-suburban travel demands, yet planning remained dominated by radial extensions and road infrastructure, including the prioritization of freeways over rail loops.[17] The concept of an orbital rail line first gained formal traction in the 1969 Metropolitan Transportation Plan, which proposed linking western and eastern suburbs via an orbital route to alleviate radial congestion, including a specific extension to Doncaster with land reservations along the Eastern Freeway corridor.[17] Property acquisition for the Doncaster line proceeded in 1975, but by 1982, the state government shelved these plans in favor of bus services and freeway expansions, citing economic unviability and shifting priorities toward automobile dependency.[17] The reserved land was sold off in 1984, effectively terminating the initiative amid broader fiscal constraints and a lack of demonstrated demand sufficient to justify the costs over radial improvements.[17] Subsequent decades saw recurring but unrealized orbital proposals, including the 1980s Victorian Transport Study's recommendation for a network incorporating loop elements and the 1991 "On the Right Track" report, which advocated orbital options for eastern suburbs to counter freeway reliance.[17] The 2002 Melbourne 2030 planning framework outlined potential orbital links, while the 2008 Victorian Transport Plan deferred such concepts to prioritize radial projects like the Regional Rail Link, completed in 2015.[17] These efforts consistently faltered due to high capital requirements, political preferences for visible road projects, underestimation of long-term orbital patronage amid low-density suburban growth, and competition from bus-based orbital services like SmartBus routes introduced in the 2000s.[17] By the 2010s, informal discussions, such as a proposed "blue orbital" east-west line through the inner north, highlighted persistent gaps but yielded no commitments, as resources focused on inner-city loops like the Melbourne Underground Rail Loop (opened 1981–1985) and metro tunnel preparations.[18][17]Initial Proposal and Early Planning (2018–2020)
The Suburban Rail Loop was first publicly proposed on 27 August 2018 by Victorian Premier Daniel Andrews as a key infrastructure pledge during the state election campaign.[19] The project envisioned a 90-kilometer underground orbital railway encircling Melbourne's central business district, linking major existing rail lines from the Frankston line in the southeast to the Werribee line in the west, passing through Melbourne Airport, and incorporating up to 12 new stations to enhance suburban connectivity.[19] At announcement, initial cost estimates for the full loop exceeded $50 billion, with the state government committing to fund it independently without seeking federal contributions.[20] Following the Labor Party's re-election on 24 November 2018, the government reaffirmed its commitment to the project, initiating detailed planning phases.[21] In September 2019, the Suburban Rail Loop Authority (SRLA) was established as a non-statutory body under the Department of Transport to oversee project development, including route assessments, stakeholder engagement, and reference design work.[22] The 2019–20 state budget allocated $300 million specifically for planning, site investigations, and early development activities.[4] Throughout 2019 and 2020, early planning focused on refining the corridor alignment and technical specifications, with reference design efforts commencing to outline feasible tunnel and station configurations.[23] On 24 November 2019, the government announced dedicated high-capacity metro trains for the loop, emphasizing its standalone operation integrated with the broader network.[24] By mid-2020, planning advanced to precinct-level engagements and environmental scoping for the initial eastern segment, culminating in the 2020–21 budget's $2.2 billion commitment to early works preparatory to construction.[25] These steps prioritized strategic corridor evaluation and market sounding without a comprehensive business case at the outset.[21]Business Case Development and Release (2021)
The Suburban Rail Loop Authority (SRLA), established on September 3, 2019, led the development of the project's business case following the Victorian Government's commitment to the initiative in August 2018.[26] The process involved technical investigations, stakeholder engagement across six phases starting mid-2019, and economic modeling commissioned from KPMG, integrated with Victoria's Value Creation Contract Framework.[26] Planning funding of $300 million was allocated in the 2019-20 state budget, with an additional $2.2 billion for SRL East early works in the 2020-21 budget, amid COVID-19 recovery considerations.[26] The Business and Investment Case was released in August 2021, articulating a strategic rationale for SRL East (Cheltenham to Box Hill, 26 km of twin-bored tunnels and six underground stations) and SRL North (Box Hill to Melbourne Airport, 34 km with seven stations) to address Melbourne's radial transport inefficiencies, urban sprawl, and projected population growth to 9 million by 2056.[26][27] It projected SRL East costs at $30.0–34.5 billion in net present value (NPV) over 14 years to 2035, with program-wide costs for both sections ranging $30.7–57.6 billion depending on sequencing options (completion by 2043 or 2053).[26][27] Expected benefits included 165,000 additional jobs in precincts by 2056, 606,000 fewer daily vehicle trips, 430,000 daily orbital passengers, and a gross state product (GSP) increase of $50.8–58.7 billion in present value, alongside public transport savings of $14.9–21.7 billion and wider economic effects like agglomeration valued at $6–9.7 billion.[26][27] Economic appraisal yielded benefit-cost ratios (BCRs) of 1.0–1.7 at a 4% discount rate for the program options, with net present values of $3.0–22.9 billion, incorporating transport user benefits, road decongestion ($10.0–14.3 billion), health improvements ($1.6–1.7 billion per section), and environmental savings ($0.5 billion).[27][26] The case emphasized connectivity to national employment clusters and activity centers, promoting 20-minute neighborhoods and reduced car dependency, with construction supporting up to 23,900 jobs statewide.[27] Value capture mechanisms, such as land tax and stamp duty from precinct developments, were proposed to offset costs.[26] Subsequent independent reviews questioned the case's robustness; the Victorian Auditor-General's Office found in 2022 that information provided to government did not adequately demonstrate the economic rationale, citing deficiencies in methodology and evidence. The Parliamentary Budget Office's analysis, using government benefits at face value, confirmed BCR sensitivity to discount rates: 1.2–1.4 at 4% but 0.6–0.7 (net cost) at 7%, excluding pre-2022 expenditures of $574 million.[28] These assessments highlighted the case's reliance on optimistic assumptions and lower discounting, potentially overstating viability from a standard fiscal perspective.[28]Approvals and Early Contracts
The approvals process for the Suburban Rail Loop (SRL) is conducted in stages, with each phase subject to separate environmental and planning assessments under Victorian law, primarily through Environment Effects Statements (EES). For SRL East, the initial stage, scoping requirements for the EES were finalized in 2020, with the draft EES exhibited for public consultation from October to December 2021. An independent inquiry and advisory committee reviewed submissions, leading to the Minister for Planning's approval of the EES on 5 August 2022, incorporating recommended conditions to mitigate environmental impacts.[29][30][31] Initial works for SRL East received separate planning approvals ahead of the full EES. In November 2020, the Suburban Rail Loop Stage One Impact Assessment and Approvals Report for Initial Works outlined site establishment activities, including ground improvement and road modifications to facilitate early construction. The Victorian Government committed $2.2 billion to fund SRL East's early works package in 2020, enabling progression without awaiting comprehensive project approvals.[32][33] Early contracts focused on preparatory activities across SRL East sites. In May 2021, the $2.2 billion Development, Initial, and Early Works Package (Works Package A) was awarded to Laing O'Rourke, covering road diversions, utility relocations, and site preparations at stations such as Box Hill and the southern stabling yard. Construction on these early works began in mid-2022, marking the project's entry into physical development phase. Subsequent contracts, including the first major tunnelling package, were awarded later, with northern tunnels contracted in November 2024 to the Terra Verde consortium.[34][35]Current Construction Status
SRL East Progress
Construction of the Suburban Rail Loop (SRL) East, spanning 26 km of twin rail tunnels and six underground stations from Cheltenham to Box Hill, commenced with initial and early works in mid-2022, focusing on site establishment, utility relocations, and geotechnical investigations across all station precincts.[9] By late 2024, works had advanced to active construction at every station site—Cheltenham, Clayton, Monash, Glen Waverley, Burwood, and Box Hill—with up to 8,000 direct jobs created and completion targeted for 2035 to enable passenger services.[36] [37] Major tunnelling contracts were awarded in phases: a $3.6 billion package in December 2023 for the 16 km southern tunnels from Cheltenham to Glen Waverley, and a $1.7 billion contract on November 10, 2024, for the northern section from Glen Waverley to Box Hill, with tunnelling scheduled to begin in 2026.[38] [39] Early works, including land acquisition and ground improvement trials, experienced minor schedule extensions, shifting completion from late 2025 to mid-2026 per Victorian Auditor-General's Office reporting, though overall project momentum continued with tunnel boring machine launch site preparations in Burwood and Clarinda by October 2025.[33] [40] Site-specific advancements included reinforced wall construction at Clayton starting mid-2025, followed by excavation in early 2026, and ongoing precinct planning hearings for Glen Waverley in July 2025 to integrate station development with urban renewal.[41] [42] Works notices through October 2025 detailed night-time operations and road closures at Glen Waverley and Box Hill, indicating sustained progress amid community notifications for noise and traffic impacts.[43]Site Preparations and Recent Milestones (2024–2025)
![Aerial view of SRL East staging area in Box Hill Gardens]float-right Site preparations for the Suburban Rail Loop East (SRL East) have advanced through the Initial Works and Early Works (IWEW) package, encompassing utility relocations, site establishments, road and tram modifications, and ground improvement trials across multiple locations.[34] These activities, initiated in 2023, continued into 2024 and 2025 to facilitate tunnel boring machine (TBM) launches and station constructions at the six planned sites: Cheltenham, Clayton, Monash, Glen Waverley, Burwood, and Box Hill.[44] The IWEW package is projected to conclude by April 2026, supporting overall SRL East completion targeted for 2035.[33] In 2024, construction crews established presence at all six SRL East station sites, marking significant progress in site mobilization and preliminary earthworks.[36] By mid-2024, halfway milestones included ongoing works at station sites and the train stabling facility, with approximately 1,500 personnel engaged by November.[45][46] At Box Hill, crews advanced TBM launch site preparations, including underground utility adjustments, as detailed in December updates.[47] Key 2025 developments included the announcement of TBM arrivals on site, with major construction commencing at the Burwood station to accommodate these machines.[48][49] Site establishment works began at Monash in mid-2025, involving vegetation removal and service demolitions, set to extend into early 2026.[50] In July, the Box Hill worksite expanded to include adjacent properties for enhanced efficiency in TBM preparations.[51] Draft structure plans for SRL East precincts were released on March 3, integrating urban development around stations.[52] Infrastructure Australia accepted the SRL East proposal for evaluation in December 2024, preceding further federal scrutiny in early 2025.[53]Proposed Extensions and Phasing
SRL North
The SRL North section forms the northern segment of the Suburban Rail Loop, extending from Box Hill to Melbourne Airport and serving key northern and outer suburban areas of Melbourne. This phase proposes seven new stations at Doncaster, Heidelberg, Bundoora, Reservoir, Fawkner, Broadmeadows, and Melbourne Airport, providing direct connections to existing rail lines and enhancing orbital travel options.[54] The route aims to integrate with SRL East at Box Hill, facilitating seamless transfers and reducing reliance on radial lines into the city center.[55] Primarily underground, SRL North is designed to alleviate congestion on roads like the Eastern Freeway and Metropolitan Ring Road by offering faster public transport alternatives, with projected benefits including shorter journey times to employment centers and improved access for over 8,500 daily regional passengers via the Broadmeadows super hub.[54] Construction of this section is anticipated to generate 5,100 jobs, while station precincts are planned to support thousands of new homes and urban development in growth corridors.[54] At Broadmeadows, more than 50% of Hume corridor passengers are expected to interchange, boosting connectivity to regional services.[54] As of 2025, SRL North remains in early planning, following the commencement of SRL East works, with construction expected to begin around 2035 after East's projected completion.[55] Full operation for this phase is forecasted for 2053, aligning with broader phasing to deliver the 90-kilometer loop incrementally.[56] The segment's development includes airport integration, addressing long-standing calls for direct rail access to Melbourne Airport from northern suburbs.[55] Independent reviews, such as those by Infrastructure Australia, have noted uncertainties in cost estimates that could impact the combined economic case for SRL East and North.[7]SRL Airport Integration
The Suburban Rail Loop's integration with Melbourne Airport, known as Tullamarine Airport, is achieved through the SRL North section, which terminates at a new underground station directly beneath the airport terminals. This 34-kilometer extension from Box Hill will include seven new stations at Doncaster, Heidelberg, Bundoora, Reservoir, Fawkner, Broadmeadows, and Melbourne Airport, providing orbital connectivity to the broader SRL network spanning Cheltenham to Werribee.[54] The airport station is designed to facilitate seamless transfers for passengers, linking to airport facilities via escalators and walkways, while enabling direct access to metropolitan, regional, and high-speed rail services.[54] Complementing this, the dedicated Melbourne Airport Rail (SRL Airport) project establishes a surface-level rail link from the airport to Sunshine Station, approximately 25 kilometers west, incorporating track reconfiguration and a new Albion station with full accessibility features. From Sunshine Superhub, services will connect via the Metro Tunnel to the CBD in under 30 minutes, extending to Cranbourne and Pakenham lines, thus integrating airport access with Victoria's regional network.[57] This configuration allows SRL orbital trains to interchange at Broadmeadows Superhub—serving an estimated 8,500 daily regional passengers—with the airport link, reducing reliance on roads and supporting electrification to Melton and future western extensions.[54][57] As of October 2025, SRL North remains in early planning, with completion projected around 2053 following SRL East's opening in 2035; reference designs for the airport station are under development to accommodate growing passenger volumes.[54] Meanwhile, Melbourne Airport Rail's preparatory works, including utilities relocation around Sunshine, are complete, with the first stage of track upgrades set to commence imminently to enable airport services by the early 2030s.[57] The Victorian Government leads both components, emphasizing reduced congestion and enhanced economic connectivity, though full loop closure via SRL West from the airport to Werribee is yet to enter detailed planning.[57][55]SRL West
The SRL West constitutes the proposed western segment of the Suburban Rail Loop, spanning from Sunshine to Werribee and connecting key western suburbs of Melbourne.[58] This section would link the Werribee line directly to the Sunshine transport super hub, facilitating orbital travel without reliance on the central business district.[58] It forms part of the broader 90-kilometre orbital network designed to integrate with existing radial lines.[1] As of October 2025, SRL West remains in the early planning phase, subject to further investigation, detailed design, and development prior to any commitment to construction.[58] No specific intermediate stations have been confirmed, though the route would enhance connectivity to precincts including Sunshine Hospital, Victoria University, and Joan Kirner Women’s and Children’s Hospital.[58] Infrastructure Australia has recommended preparing a detailed business case for SRL West, alongside SRL North, to support potential federal funding assessments.[7] SRL West is planned for integration with complementary projects, including the Melbourne Airport Rail Link at Sunshine, the Metro Tunnel project, and the Sunbury Line Upgrade, to create a cohesive western transport corridor.[58] This linkage would enable faster journeys from Werribee to Melbourne Airport and onward connections, reducing travel times and improving access to employment and services in the region.[58] The section anticipates supporting precinct development with additional housing near stations to capitalize on enhanced public transport accessibility.[58] No timeline for construction or completion has been established, reflecting its status as a later phase following SRL East.[58] The Victorian government positions SRL West as a means to boost economic activity in underserved western areas by promoting job proximity and efficient commuting.[58]Economic Analysis
Cost Estimates and Funding Mechanisms
The Suburban Rail Loop East, the initial 26 km stage from Cheltenham to Box Hill, has an estimated capital cost of $30–34.5 billion, with completion targeted for 2035.[3] This figure reflects updates from earlier projections, incorporating inflation and design refinements since the 2021 business case, though independent assessments anticipate potential overruns due to 2020 baseline pricing amid post-pandemic economic pressures.[6] The Victorian Parliamentary Budget Office estimated lifecycle costs for SRL East, including asset works, renewals, and operations over 50 years, at $84.1 billion as of March 2024.[4] For the full 90 km loop encompassing east, north, and west phases, capital construction costs are projected to exceed $100 billion, with total lifecycle expenses—including maintenance and operations—potentially surpassing $200 billion over decades.[59] The Parliamentary Budget Office's analysis for SRL East and North phases alone forecasted $216.6 billion in combined lifecycle costs, dominated by $133.9 billion in asset works and renewals.[4] These estimates draw from government budget papers and independent fiscal modeling, highlighting escalation from initial 2018–2021 figures of around $50 billion for the full project due to scope expansions, supply chain disruptions, and labor shortages.[60] Funding for the project relies predominantly on Victorian state borrowing and budget allocations, with the government committing $9.3 billion to SRL East as of August 2025.[61] Early works packages, valued at $1.7 billion for certain components, are fully state-funded without private partnerships.[55] Federal contributions have been limited, totaling approximately $2.2 billion toward SRL East, though ongoing negotiations seek additional support amid fiscal constraints.[62] Proposed mechanisms include value capture from urban renewal around stations, such as developer levies on increased land values, and a dedicated fund drawing from redirected existing tax revenues like payroll or property taxes to address an estimated $11.5 billion shortfall for later phases.[63][64] No major private financing models, such as public-private partnerships for operations, have been finalized, leaving the bulk of debt servicing on state taxpayers.[33]Patronage Forecasts and Benefit-Cost Assessments
The Suburban Rail Loop is projected to generate approximately 400,000 daily trips by 2051, positioning it as Melbourne's busiest standalone rail line with bi-directional peak flows and around 80% capacity utilization in the morning peak.[63] Updated modeling extends this to over 430,000 daily orbital journeys by 2056, alongside more than 230,000 additional public transport trips across Melbourne, derived from the Victorian Integrated Transport Model (VITM) and agent-based simulations incorporating pre-COVID-19 travel patterns and land-use integration.[65] These forecasts assume high-frequency services (up to 24 trains per hour in peaks) and integration with existing radial lines, though they face uncertainties from remote work trends and autonomous vehicle adoption, potentially reducing demand.[65] The 2021 business case, prepared by KPMG for the Victorian government, estimated a base benefit-cost ratio (BCR) of 1.1–1.7 for the East and North sections combined (using a 4% social discount rate over a 50-year appraisal period), yielding a net present value (NPV) range of $3.0 billion to $22.9 billion in 2020 dollars.[65] This incorporated conventional benefits (e.g., travel time savings, reduced congestion) plus wider economic impacts like productivity gains from job agglomeration, quantified via tax revenue proxies and imperfect market adjustments per Australian Transport Assessment and Planning (ATAP) guidelines.[65] Sensitivity tests adjusted for COVID-19 (BCR 0.8–1.4) and high rideshare penetration (0.8–1.3), highlighting reliance on optimistic assumptions such as 1.5% annual productivity growth and government debt financing during construction.[65] Independent analyses have yielded lower BCRs, questioning the government's figures due to the low discount rate—which favors capital-intensive, long-horizon projects—and potential overstatement of wider benefits. The Victorian Parliamentary Budget Office's 2024 review, applying a central 7% discount rate, calculated a BCR of 0.6–0.7 for East and North (NPV -$10.6 billion to -$7.4 billion), rising to 1.2–1.4 only at 4% with full benefits inclusion; higher 10% rates produced 0.3–0.4.[28] Infrastructure Australia's January 2025 Stage 3 evaluation referenced the government's 1.1–1.7 BCR but flagged overstated economic benefits ($48.5–$58.7 billion) amid cost escalations beyond the 2020 $34.5 billion estimate, recommending updated appraisals before further federal funding.[7] These critiques underscore methodological divergences, with government models emphasizing urban consolidation and precinct job growth (e.g., 545,000 jobs by 2056) potentially inflating returns relative to conservative baseline scenarios.[7][28]| Source | BCR Range | Discount Rate | Key Notes |
|---|---|---|---|
| Government Business Case (2021) | 1.1–1.7 | 4% | Includes wider economic benefits; pre-escalation costs.[65] |
| PBO Analysis (2024) | 0.6–0.7 (central) | 7% | Net costs at standard rates; aligns with government at 4%.[28] |
| Infrastructure Australia (2025) | 1.1–1.7 (referenced) | 4% | Benefits potentially overstated; calls for revisions.[7] |