HS2 is set to ditch some of its most ambitious railway technology in a bid to make Britain's most troubled infrastructure project easier to finish.

A report by spending watchdog the National Audit Office (NAO) published on Monday reveals the Department for Transport (DfT) has agreed changes to simplify parts of the railway's technical specification as part of HS2's latest reset, which began in January 2025. The report is the first full assessment of the project since the reset got underway.

The transport secretary asked HS2 Ltd in January to examine whether running trains more slowly could reduce cost, schedule risk, and testing time. The company responded by proposing a maximum operating speed of 320 km/h rather than 360 km/h.

One of the biggest casualties is automatic train operation (ATO), a system that would have allowed trains to operate automatically under normal conditions while a driver remained onboard to supervise. Rather than pursue a bespoke setup, HS2 now plans to drop ATO from Phase 1, allowing it to simplify the signaling system by adopting technology already proven elsewhere.

HS2 Ltd estimates the revised specification could save between £1 billion and £2.5 billion and allow the railway to open at least a year earlier than previously expected.

The NAO, however, warned that the savings remain uncertain, noting that slower journeys would reduce the railway's long-term benefits by around £1.3 billion.

According to the report, simplifying the railway would also avoid the time and expense of proving it could safely operate at 360 km/h while avoiding the risk that testing might ultimately show the higher speed was not feasible.

As of the end of March, DfT and HS2 Ltd had spent £46.8 billion on HS2, including the canceled Phase 2. HS2 expects the reset itself to cost £153 million before concluding in spring 2027.

The watchdog said DfT and HS2 Ltd were taking "reasonable steps" to revise the project's cost and schedule, but warned the figures published in May still carry "a high level of uncertainty."

HS2 is now working toward what it calls "a fully assured and endorsed revised baseline," validating the quality of its data and assumptions, including with contractors, and resolving inconsistencies before using it to manage delivery.

The NAO also urged ministers not to rush the exercise simply to hit the current deadline. It recommended reviewing this autumn whether completing the reset by spring 2027 remains realistic and, if necessary, extending the timetable until the program is "fully on a stable footing."

Beyond that, the watchdog said HS2 should continue focusing on cost, schedule, and commercial management, identify capability gaps before they become critical, and apply lessons from previous rail programs on systems integration and the complexity of bringing an entire railway together. It also said that decisions on the future train fleet should align with the wider rail network to ensure sufficient capacity and maximize the project's benefits.

For years, HS2 has been trying to build the railway of the future. The latest reset suggests ministers would now settle for building one that actually opens. ®