For almost two years, thousands of passengers in Sydney’s inner west and south-west have queued daily for every commuter’s nightmare: the replacement bus.In Marrickville, the queue for the bus to nearby Sydenham metro station snakes past artisan butchers and bánh mi shops. During the morning peak, commuters sometimes have to wait for three or four bright-pink buses before they can secure a spot.But with “through running” testing starting on Tuesday on the Sydenham to Bankstown metro extension, which passes through Marrickville, those replacement buses will soon be just a bad memory.Just don’t ask the state government for a start date for passenger services.Sign up for the Breaking News Australia email“We are still in the hands of the national safety regulator, and we don’t want to tempt fate with a date that we don’t meet,” the premier, Chris Minns, says on Tuesday, pre-empting questions from reporters ahead of a media opportunity to ride all the way from Sydenham to Bankstown.As the doors beep shut at Sydenham, the prospect of journeys to Bankstown in less than half an hour feels very real. Five minutes later, the train has not moved.“I reckon it’s going to be hard to make 24 minutes,” jokes the premier, who gets off at the first stop: Marrickville.The NSW premier, Chris Minns, at Sydenham station. Photograph: Bianca de Marchi/AAPSoon we are zooming through the inner west at unprecedented speeds of up to 100km/h, the Cooks River passing underneath.As we pull up to stations – Campsie, Canterbury, Belmore – the doors open to reveal workers in orange hi-vis, removing plastic wrapping from benches, fixing signage and working on lifts.These former T3 Bankstown line stations have been closed since September 2024, following the opening of the wildly popular city metro extension the month before.Since then, metro trains have been running from Tallawong in the north-west via Central station, terminating at Sydenham. As of Tuesday, after passengers have disembarked at Sydenham, some trains will carry on – or “through run” – to Bankstown. They will ramp up so that every service will run to Bankstown before the first passenger services begin.Last month, the Sydney Morning Herald reported Sydney Metro was targeting mid-October.The acting NSW transport minister, Jenny Aitchison, who on Tuesday stays on board all the way to Bankstown and back, refuses to be drawn on the date. In response to another question, she later says: “If you look at the revised program that was put in place, I think we’re meeting all the targets along that.”So why has the closure, which the former Coalition government predicted in 2018 would take three to six months, and which the Minns government said would take at least a year, lasted so long?Aitchison attributes the delays to the “heritage issues on the network”.skip past newsletter promotionafter newsletter promotionThe Southwest Metro train stationed at Sydenham station in Sydney on Tuesday. Photograph: Bianca de Marchi/AAPIt’s a view echoed by Alia Karaman, the project director for Sydney Metro Southwest, who tells reporters: “We’re a brownfield railway, there are unexpected hiccups every day.”Outside Lakemba, there is an unexpected stop. The train grinds to a halt, and the horn goes off.The faces of the dozens of transport officials drop. Something has triggered the network alarm system. There may be something blocking the track, they worry. We may have to turn back.Thankfully, we start moving again, and at pace. From the time the train actually left Sydenham to when doors open on the rejuvenated Bankstown station, it has taken just over 26 minutes, despite the interruption.It’s not the top speed yet, but it reflects the savings that will be delivered across the network. A journey from Bankstown to Central is expected to take 28 minutes – a six-minute saving compared with the former rail line. Lakemba to Victoria Cross, meanwhile, is expected to take 37 minutes – a 24-minute saving.The government says the extension will deliver capacity for an additional 17,000 people during peak hours. But will that be enough? Aitchison says Transport for NSW has modelled demand. “We know there’s obviously going to be demand, but it is hard to know that until it actually starts.”For now, Sydneysiders have more interruptions to deal with, including full line closures across the whole metro line in coming weekends in July.At times during the journey to Bankstown and back to Sydenham, the replacement bus can be glimpsed running alongside the train – the status quo, for now.