Train services in Sydney and across other Australian cities are experiencing major delays due to a signalling system problem, according to multiple reports. All outlets state that two rail lines are primarily affected, while disruptions spread beyond those routes and create knock-on effects for the wider network. The delays are described as significant enough to disrupt normal operations and propagate through connected services, suggesting traffic management and scheduling are impacted across the rail system rather than only on isolated segments. While the articles focus on the core affected routes, they also emphasise that commuters may experience broader delays, including interruptions to services that rely on the same signalling infrastructure and network flow. The reports do not indicate a specific cause beyond the signalling issue, nor do they provide detailed repair timelines in the supplied summaries. Overall, the shared picture is that a signalling fault is driving substantial operational delays, with two main lines affected first and additional service impacts occurring throughout the rail network.