Revealed: The four new tunnels Brisbane needs to ease traffic congestion
Brisbane's peak-hour traffic has evolved into gridlock … so could a network of strategic tunnels be the city's best escape route? AI v THE EXPERTS
Brisbane commuters are suffering through four waves of peak-hour traffic every day – so what is the solution?
In October 2025 it was revealed even flexible work schedules are failing to slow the exploding number of cars on Southeast Queensland roads.
Transurban traffic data showed Brisbane’s congestion curve was widening with dual peaks emerging early-morning and midafternoon.
So are tunnels the answer? If so, where and when?
We’ve gone to a university professor, a transport advocate and AI to delve into tunnels and whether they’re Brisbane’s best chance of moving forward. Who do you agree with?
What the evidence shows from existing tunnels
■ Legacy Way (M5) — a 4.6–5km toll tunnel linking the Western Fwy (Toowong) to the Inner-City Bypass — is documented by the Australian Government as easing congestion and reducing travel times on this corridor.
It received $500m federal funding and was completed in 2015.
Independent case reporting notes that peak-hour travel time was roughly halved when it opened, underscoring the scale of congestion relief possible when long, signal-free links are added to the network.
■ Clem7 and AirportlinkM7 form part of Transurban’s Brisbane network tying the northside (M7) to inner-city links, removing signalised intersections and adding river-crossing capacity — both fundamentals for reducing stop-start congestion.
■ Bus/metro tunnelling works under Adelaide Street connect the South East and Inner Northern Busways, enabling about 1400 daily services to bypass CBD surface conflicts, improving reliability and person-throughput.
Where the worst pressure is now
■ Gateway Motorway (north) records some of Brisbane’s sharpest peak slowdowns (PM outbound speed drops of 45–49km/h on certain sections), highlighting sustained capacity pressure on the northside approach to the Bruce Highway.
■ Gympie Road corridor (Bruce Hwy approach) is flagged by the state for bypass solutioning; TMR’s open datasets and BSTM screenline counts identify consistently high flows on state-controlled arterials in this sector.
Why tunnels (according to AI)
■ They avoid signals and conflict points: Removing dozens of lights (e.g., the 19 signals cited on Gympie Rd) is the single biggest way to stabilise travel times and cut queuing.
They add cross-river capacity where bridges and streets are saturated: East–West would create another grade-separated river link, a known constraint for east – west movements.
■ They protect the surface street grid for local access and buses: When tunnels go offline, the citywide delays demonstrate how much surface capacity they free during normal operation (Legacy Way’s outage pushed ICB/Milton Rd to 20–30 minute delays).
■ They complement rail/bus tunnels that shift trips off roads: The State’s Cross River Rail (10.2km line with 5.9 km twin tunnels) is explicitly designed to relieve inner-Brisbane capacity constraints and, by doing so, frees road space and improves network performance.
Tunnels to prioritise (according to AI)
1) Gympie Road Bypass Tunnel (Kedron–Carseldine)
What it is: A tolled, four-lane (two each way) bypass tunnel under Gympie Rd from Kedron to Carseldine, skipping 19 traffic lights. Led by North Brisbane Infrastructure (QIC subsidiary) for the Queensland Government.
Congestion benefit evidence: Government statements cite up to 32 minutes saved per day for return peak trips, with reductions in rat-running and improved safety from diverting through-traffic out of local streets.
By plugging directly into the AirportlinkM7/Clem7/ICB spine at Kedron, it removes stop-start friction from one of Brisbane’s busiest urban arterials.
Why it matters network-wide: It gives northside – CBD and north – south movements a fast, reliable path that doesn’t consume scarce surface signal time on Gympie Rd, and it relieves pressure feeding the Gateway north where RACQ reports the largest peak speed collapses.
Status: Investment proposal merits confirmed by the State; no construction funding announced yet (i.e., still pre-contracts).
2) East–West Link Tunnel (Toowong–Buranda, cross-river)
What it is:A tolled road tunnel linking the Western Freeway at Toowong to the Pacific Motorway at Buranda, envisioned to provide another cross-river, motorway-grade link and remove traffic from Milton Rd, Coronation Dr and the Riverside Expressway that is just “passing through.”
This is the fifth (unbuilt) TransApex link on record in Brisbane City Council materials tabled in Queensland Parliament.
Congestion benefit logic in the official plan: A continuous east – west motorway-standard tunnel eliminates multiple signalised corridors and creates additional cross-river capacity, reducing inner-city weaving and freeing CBD surface capacity. (As documented in Council’s TransApex program.)
Status: A recognised Council proposal but not in current state program/funding; would require a new business case consistent with Infrastructure Australia’s Assessment Framework before progressing.
3) Targeted bus/metro tunnelling (CBD and northward) to increase person-throughput
What it is: Brisbane has delivered the Adelaide Street bus tunnel as part of Brisbane Metro; the Australian Government has funded a Detailed Business Case for Metro northern extensions (future lines and potential grade separations).
Congestion benefit evidence: Dedicated underground bus/metro links remove buses from mixed traffic, unclog surface intersections, and raise corridor person-capacity — a complementary way tunnels cut road congestion by mode shift and reliability.
Status: Adelaide St delivered; northern extension business case is funded (not construction).
4) North-West Transport Corridor (NWTC)
What it is: A preserved transport corridor dating back to the Wilbur Smith plan; TMR retains it for potential future arterial/rail solutions in Brisbane’s north-west.
Various underground options have been investigated over time. Any tunnel component here would need fresh business case work.
What the professor says
Griffith University transport expert, Adjunct Professor Matt Burke, said that instead of more tunnels, the existing tunnels needed to be better used.
Prof Burke, the CEO of Bicycle Queensland, said the current system of free surface roads, relatively high tunnel tolls and no discounts to encourage motorists to use several tunnels to extend their trips underground was a recipe for traffic snarls.
“What we have created is basically a pro-congestion charging scheme. If you want to generate more congestion, this is how you would go about doing it,’’ Prof Burke said.
He said the reason the Toowong to Buranda tunnel never went ahead was that it was the worst of former Lord Mayor Campbell Newman’s “Trans Apex’’ network of bridges and tunnels.
It was long and would therefore be expensive, there was less demand for it from motorists and viable surface alternatives.
While a Kedron-to-Chermside tunnel would help deal with growing freight and passenger movement on the northside, he said a better alternative for moving large numbers of people would be to replicate Cross River Rail on the northside.
“At the moment you have the future Sunshine Coast line, the Redcliffe, Ferny Grove and Caboolture lines all feeding into Bowen Hills station, and the northside also has the windiest city rail lines in the country,’’ he said.
Mr Burke said it was unlikely any new tunnel would pass a cost-benefit ratio analysis if it was free and if it was tolled, experience with the Clem7, Legacy Way and Airport Link showed it would likely be under-utilised.
What RACQ says
RACQ head of public policy, Dr Michael Kane, said while more Metro tunnels and a northwest underground connection were needed, getting a proper plan in place first for the city was their priority.
“There’s more than enough work to start with on finishing motorways and interchanges including the Logan and Gateway motorways,” he said.
“By 2046 we will be the same size as Sydney. Sydney has a lot of tunnels and tolls and is still the most congested city in Australia so we don’t want to end up like them.
“I don’t think any tunnel is a priority in the next decade and we don’t want to see projects that don’t fit into a network plan.”
Dr Kane said however that a connection from the Centenary Mwy through to Brisbane’s northwest suburbs would be vital in coming years and some of that would have to be underground.
The RACQ had no preference for a tunnel route on the northside despite some calls for it to follow Gympie Rd and others pushing the Northwest Corridor from Kedron to Chermside.
He also said the priority extension for Metro was from Herston to Chermside.
“There’s are 26 sets of lights. You can’t have a mass public transport system with 26 intersections,” he said.
“Whatever we do, we need to get it right. It needs to be spot on which is why we shouldn’t be talking about specific projects before we get a proper network plan.”
Possible priorities (according to AI)
■ Advance the Gympie Road Bypass Tunnel to a full Business Case and funding decision
Use TMR’s BSTM and traffic census datasets to quantify corridor-wide impacts (Airportlink/ICB interfaces, Bruce Hwy approach, local rat-running) and to verify the 32 minutes per day commuter saving claim in the investment proposal material.
■ Commence a modern business case for the East–West Link Tunnel (Toowong–Buranda)
Re-test the TransApex alignment and portals against today’s demand (BSTM), current land use, and construction methods. Submit under Infrastructure Australia’s Assessment Framework (Stage 3) to enter national funding pipelines.
■ Lock in the person-throughput gains from bus/metro tunnelling
Finish the Metro northern extension business case and identify any additional short tunnel sections/underpasses that remove remaining CBD and Chermside-axis bus conflicts, building on the benefits already achieved with the Adelaide St tunnel.
Expected congestion wins
Travel-time reliability: The federal project page for Legacy Way cites congestion easing and travel time reduction; Brisbane’s experience shows signal-free links deliver step-change reliability v repeated surface widening.
Northside relief: The Gympie Road Bypass would divert through-traffic out of 19 signals and reduce rat-running — exactly where RACQ identifies the steepest peak slowdowns feeding the Bruce/Gateway system.
System resilience: The February 2025 Legacy Way incident demonstrated how dependent the city is on these grade-separated links; more tunnels provide redundancy and keep freight and commuter flows moving during incidents.
Mode shift (freeing road space): Cross River Rail adds core rail capacity (with 5.9 km of twin tunnels under the river/CBD), which the business case identifies as essential to relieving inner-city constraints and improving conditions for other modes, including roads.
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