And there are doubts over whether the system – a digital-radio upgrade – will be in place by mid next year, almost five years after the initial deadline to install the $225 million project.

Tightly held government documents show that a digital train-radio system, which would allow drivers, controllers, signallers, guards and trackworkers to communicate with one another, has been plagued by delays and overruns since the previous government first promised to introduce it by 2010.

For drivers, the lack of a digital-radio system exposes them to “black spots” on the city’s rail network, where the current analogue radio system is erratic.

Documents obtained by Fairfax Media (PDF 2.9MB) show that the latest attempts to get the project back on track remains at risk of missing its new deadline.

“At this stage the forecast date for final completion of July 2015 is noted with concern,” says a Transport for NSW update into the project, obtained using freedom of information laws.

Following the Waterfall train disaster on January 2003, an inquiry by Peter McInerney highlighted the long-standing failure to upgrade communications technology on Sydney and NSW trains.

“The Waterfall, Hexham and Glenbrook rail accidents, and the other accidents considered by the Glenbrook Inquiry, all point strongly to the need for compatibility of communications systems throughout the network,” Justice McInerney’s report said. “It is essential that drivers, controllers, signallers, guards and trackside work gangs communicate using the same technology,” the report said.

In response, the former Labor government said it would introduce a digital-radio system across the network by the end of 2010. But the government did not sign a contract to deliver the system until 2009. That $225 million contract, with infrastructure company UGL, envisaged finishing the project by 2012.

But after the O’Farrell government came to office, the contract was renegotiated and the completion date pushed back to April next year. That date has since been pushed to next July. Documents also show that there have since been multiple commercial disputes between UGL and the government that may have driven up the project’s cost.

Transport Minister Gladys Berejiklian blamed the delays on the former government, and said the project would be finished by July.

“It is a disgrace that Labor left this project in such a mess,” Ms Berejiklian said.  “The safety of customers is a priority for the NSW government and I'm pleased this complex project is now back on track."

Bob Newham, an organiser for the Rail, Tram & Bus Union, said one of the problems with the analogue radio system was that it was “patchy.” Mr Newham cited the Blue Mountains and the Hawkesbury River as areas where drivers might find they were in a communications “black spot”.

“You still have emergency functionality but that only applies to trains within that specific area,” Mr Newham said. “If you saw trespassers on the track and you needed to ring the signal box to alert them, you would not have that capability,” he said. The analogue system also does not allow drivers to communicate with other trains; for instance, to tell an oncoming train that something is wrong.

A spokeswoman for Transport for NSW said the government found the project had been “mismanaged” when it came to office.

“The project deadline was put under continuing detailed review as the government worked to resolve the situation and bring the project back on track,” the spokeswoman said. “DTRS is a very complex and difficult project that includes the design and installation of a bespoke communications system, tailored to the needs of a large, complex rail network.”