What the current evidence can answer
Important: this is a mixed opening-transition reference, not a pure pre-opening baseline.
Questions answered within the current mixed-period reference
Where is combined monitored overnight two-way freight activity currently greatest?
Current answer: West Gate Bridge ranks first among governed paired whole-site assets, averaging 2,202.1 normalised combined truck passings over an eight-hour night.
Evidence: Stage 22 governed paired-site ranking; 148 eligible West Gate paired nights.
Next evidence: Compare the same governed measure across separately defined pre-opening, transition and later operating windows.
Boundary: Passings are sensor observations, not unique trucks or complete journeys.
Is West Gate Bridge freight activity sustained in both directions?
Current answer: Yes. Sustained two-way pressure occurred on 81.8% of eligible nights. 87.8% of nights were classified as balanced.
Evidence: Stage 22 paired inbound/eastbound and outbound/westbound evidence.
Next evidence: Compare the same percentages across separately governed opening-period segments and later operating periods.
Boundary: The measure establishes two-way monitored activity; it does not identify individual truck routes.
Which direction currently carries the larger share, and when does combined freight peak?
Current answer: Inbound/eastbound is the overall dominant direction with 55.8% of paired passings. Median directional imbalance is 11.3%. The combined peak is 5:00 am-6:00 am, averaging 621.9 truck passings.
Evidence: Stage 22 paired whole-site direction and hourly profile.
Next evidence: Test whether direction shares and the peak hour differ between pre-opening, transition and later operating windows.
Boundary: This is monitored bridge activity, not origin-to-destination routing evidence.
How do both West Gate Bridge directions rank for overnight operating-speed pressure within the governed reference period?
Current answer: Outbound/westbound ranks 3 with a pressure index of 37.86. Inbound/eastbound ranks 5 with an index of 30.03.
Evidence: Stage 23A.4 strategic-network Tier A ranking for the mixed opening-transition reference period.
Next evidence: Compare later operating-period observations against the frozen reference and separately build a clean segmented pre-opening versus operating-period analysis.
Boundary: The pressure index is relative point-speed pressure, not travel delay.
Which West Gate Bridge direction is more pressured within the current reference period?
Current answer: Outbound/westbound. Its observed speed is 84.1% of reference, compared with 89.9% inbound. It is below 90% of reference during 40.0% of eligible hours, versus 31.3% inbound.
Evidence: Stage 23A.4 directional pressure measures.
Next evidence: Test whether either or both directional gaps narrow in later operating periods and in a separately segmented opening analysis.
Boundary: The comparison does not convert the speed gap into journey-time savings.
Which West Gate Bridge direction is less reliable from night to night within the current reference period?
Current answer: Inbound/eastbound is slightly less reliable. Its P90-P10 nightly spread is 32.3 percentage points and it ranks second for network reliability risk. Outbound/westbound has a 30.7-point spread and ranks third.
Evidence: Stage 23A.4 network reliability-risk ranking.
Next evidence: Compare later-period P90-P10 and interquartile spreads, and separately evaluate segmented pre-opening and operating-period windows.
Boundary: A larger spread means less consistency; it does not by itself identify the cause.
Is bridge pressure occasional, or does it recur for sustained periods within the current reference?
Current answer: It is recurring. Sustained-pressure nights occur on 51.9% of outbound eligible nights and 42.0% of inbound eligible nights. Both directions recorded worst-night runs spanning all eight overnight hours.
Evidence: Stage 23A.4 sustained-pressure and longest-run measures.
Next evidence: Measure whether sustained-night frequency and longest runs fall in later operating periods and across the segmented opening windows.
Boundary: Worst-night runs establish persistence within the monitored overnight window, not a full-day condition.
During which overnight hours is West Gate Bridge pressure most pronounced within the current reference?
Current answer: Outbound/westbound has its worst governed hour at 12:00 am-1:00 am; inbound/eastbound at 10:00 pm-11:00 pm. Complete profiles are available for every hour from 10 pm to 6 am.
Evidence: Stage 23A.4 eight-hour directional profiles.
Next evidence: Compare each later operating-period hour with the matching frozen hourly reference and rebuild the profiles for segmented opening windows.
Boundary: The profiles are detector-hour evidence and should not be described as complete corridor travel times.
Where is overnight strategic-network speed pressure greatest within the governed reference period?
Current answer: Tullamarine FWY Inbound - Before Mickleham Rd (SB) ranks first with a pressure index of 56.03. Truck speed is below 90% of reference during 75.5% of eligible hours, with sustained pressure on 76.9% of eligible nights.
Evidence: Stage 23A.4 strategic-network pressure ranking for the mixed opening-transition reference.
Next evidence: Track whether the leading pressure location changes in later operating periods and between segmented windows.
Boundary: A rank identifies relative monitored pressure, not the cause or a complete journey impact.
Which monitored community-road location has the greatest overnight pressure within the governed reference period?
Current answer: Sydney Rd and Jukes Rd (SB) ranks first with a pressure index of 34.11. It is below 90% of reference during 47.1% of eligible hours and records sustained pressure on 69.8% of eligible nights.
Evidence: Stage 23A.4 community-road Tier A ranking for the mixed opening-transition reference.
Next evidence: Use the same measures in segmented windows and later operating periods to test community-road relief.
Boundary: The ranking covers governed monitored headings, not every local road.
Is leading overnight freight pressure concentrated or evenly distributed within the current reference?
Current answer: It is concentrated. All five leading strategic-network pressure headings are on the Tullamarine Freeway or West Gate Bridge. Both bridge directions are in the top five.
Evidence: Stage 23A.4 network top-five pressure ranking for the mixed opening-transition reference.
Next evidence: Test whether later-period top-five pressure becomes less concentrated or moves elsewhere, and compare segmented windows.
Boundary: Concentration in monitored rankings does not establish why those locations are pressured.
How much governed evidence supports the current reference-period findings?
Current answer: The speed reference contains 269 Tier A headings, 2,152 reference-ready heading-hours, 374,900 complete speed hours and 46,697 eligible heading-nights. Stage 22 adds 119 paired sites, 163,819 complete paired hours and 20,401 eligible paired nights.
Evidence: Governed Stage 22 and Stage 23A.4 manifests.
Next evidence: Preserve equivalent quality gates when producing segmented opening windows and later-period comparisons.
Boundary: Evidence strength supports comparison; it does not remove the need to account for external conditions.
Which headings are suitable for public comparison, and what fixed reference can later operating periods be tested against?
Current answer: 269 Tier A headings qualify for full temporal comparison; 12 Tier B headings are descriptive only; 2 Tier C headings are excluded. Later periods can be compared with VTA_STAGE23A4_P85_20251101_20260521, but that reference spans 1 November 2025 to 21 May 2026 and is not a pure pre-opening baseline.
Evidence: Stage 23A.3 tiers and Stage 23A.4 frozen mixed-period opening-transition reference.
Next evidence: Keep the frozen reference for later-period monitoring, and separately build pre-opening, transition and early-operation windows for a clean opening-effect evaluation.
Boundary: The P85 reference is an observed upper-normal point speed, not a posted speed limit or a pure pre-opening counterfactual.
Opening segmentation or later-period evidence pending
Can the current Stage 23A.4 reference by itself establish a clean before-versus-after West Gate Tunnel opening effect?
Current answer: No. The tunnel opened on 14 December 2025, while the reference spans 1 November 2025 to 21 May 2026. It contains 43 pre-opening nights and 159 nights on or after opening, so it is a mixed opening-transition reference.
Evidence: Existing governed mixed-period opening-transition reference.
Next evidence: A governed Stage 23A.5 segmentation with separate pre-opening, opening-transition and early-operation windows, each subjected to fresh coverage and density gates.
Boundary: No West Gate Tunnel opening benefit or failure verdict can be issued from the mixed-period reference alone.
Did West Gate Bridge operating-speed pressure improve in later operating periods?
Current answer: The current mixed-period inbound and outbound reference is established separately, including pressure index and threshold occurrence.
Evidence: Existing governed mixed-period opening-transition reference.
Next evidence: A governed later operating-period comparison against the frozen reference, plus a separately segmented opening analysis.
Boundary: No West Gate Tunnel opening benefit or failure verdict can be issued from the mixed-period reference alone.
Did West Gate Bridge reliability improve in later operating periods?
Current answer: Current P10-P90, P25-P75, worst-night and sustained-run measures are established in both directions.
Evidence: Existing governed mixed-period opening-transition reference.
Next evidence: Later-period nightly distributions with comparable coverage, plus segmented pre-opening, transition and operating windows.
Boundary: No West Gate Tunnel opening benefit or failure verdict can be issued from the mixed-period reference alone.
Did freight redistribute from community roads onto intended strategic routes?
Current answer: Current community, network, directional and two-way monitoring reference conditions are available.
Evidence: Existing governed mixed-period opening-transition reference.
Next evidence: Segmented and later-period TIRTL and SCATS counts across the same monitored community and strategic-route set.
Boundary: No West Gate Tunnel opening benefit or failure verdict can be issued from the mixed-period reference alone.
Did monitored Port of Melbourne approaches improve in later operating periods?
Current answer: Existing monitored approach volumes, pressure and reliability form an opening-transition reference, not a pure pre-opening baseline.
Evidence: Existing governed mixed-period opening-transition reference.
Next evidence: Equivalent segmented and later-period evidence across the complete selected port-approach chain.
Boundary: No West Gate Tunnel opening benefit or failure verdict can be issued from the mixed-period reference alone.
Did the worst overnight operating hours improve in later periods and in both directions?
Current answer: Eight separate hourly references and pressure profiles are frozen for every Tier A heading, with bridge directions kept separate.
Evidence: Existing governed mixed-period opening-transition reference.
Next evidence: Later-period hourly observations compared hour-for-hour, plus segmented opening profiles without averaging directions together.
Boundary: No West Gate Tunnel opening benefit or failure verdict can be issued from the mixed-period reference alone.
Did pressure reduce, redistribute as intended, or move elsewhere?
Current answer: The current monitored network ranking and community/network separation establish the mixed-period opening geography.
Evidence: Existing governed mixed-period opening-transition reference.
Next evidence: Segmented and later-period network-wide change maps and corridor comparisons, including locations outside the immediate project footprint.
Boundary: No West Gate Tunnel opening benefit or failure verdict can be issued from the mixed-period reference alone.
Were any later measured improvements sustained?
Current answer: The frozen reference and quality gates are ready for repeated later-period monitoring.
Evidence: Existing governed mixed-period opening-transition reference.
Next evidence: Separate stable operating-period assessments, followed by 90-, 180- and 365-day evaluations with seasonal, roadwork and incident context.
Boundary: No West Gate Tunnel opening benefit or failure verdict can be issued from the mixed-period reference alone.
Questions requiring additional evidence
What was the complete origin-to-destination truck journey-time saving?
Current answer: Not established by the current detector dataset alone.
Evidence: Current TIRTL and SCATS evidence can describe monitored conditions and changes, but not this claim by itself.
Next evidence: Linked journey observations or approved segment travel-time data covering complete freight paths.
Boundary: Do not infer this result from point speeds or sensor passings without the stated additional evidence.
How many truck-hours were saved or lost?
Current answer: Not established by the current detector dataset alone.
Evidence: Current TIRTL and SCATS evidence can describe monitored conditions and changes, but not this claim by itself.
Next evidence: Approved segment distances, governed reference travel times and a defensible method for aggregating detector evidence.
Boundary: Do not infer this result from point speeds or sensor passings without the stated additional evidence.
How many unique trucks used each route?
Current answer: Not established by the current detector dataset alone.
Evidence: Current TIRTL and SCATS evidence can describe monitored conditions and changes, but not this claim by itself.
Next evidence: Privacy-governed vehicle linkage or another method that can distinguish unique vehicles from repeated sensor passings.
Boundary: Do not infer this result from point speeds or sensor passings without the stated additional evidence.
Where did individual freight journeys begin and end?
Current answer: Not established by the current detector dataset alone.
Evidence: Current TIRTL and SCATS evidence can describe monitored conditions and changes, but not this claim by itself.
Next evidence: Origin-destination or linked trajectory evidence. A detector passing alone cannot identify the complete journey.
Boundary: Do not infer this result from point speeds or sensor passings without the stated additional evidence.
What monetary productivity benefit was delivered?
Current answer: Not established by the current detector dataset alone.
Evidence: Current TIRTL and SCATS evidence can describe monitored conditions and changes, but not this claim by itself.
Next evidence: Governed travel-time savings, vehicle operating costs, freight value and economic appraisal assumptions.
Boundary: Do not infer this result from point speeds or sensor passings without the stated additional evidence.
What emissions benefit was delivered?
Current answer: Not established by the current detector dataset alone.
Evidence: Current TIRTL and SCATS evidence can describe monitored conditions and changes, but not this claim by itself.
Next evidence: Distance, vehicle technology, speed-cycle and emissions-model inputs beyond the current detector pressure evidence.
Boundary: Do not infer this result from point speeds or sensor passings without the stated additional evidence.
Can every observed change be attributed solely to the project?
Current answer: Not established by the current detector dataset alone.
Evidence: Current TIRTL and SCATS evidence can describe monitored conditions and changes, but not this claim by itself.
Next evidence: A causal evaluation controlling for incidents, roadworks, economic conditions, seasonality, enforcement and other network changes.
Boundary: Do not infer this result from point speeds or sensor passings without the stated additional evidence.