Public servants faced a series of questions about the 18-month delay to finishing the $31 million road project during a Legislative Assembly committee hearing on Thursday, in the wake of auditors being called in to examine a series of problems on the job.

The audit underway is also examining the governance and management of the contracts for the duplication project amid a series of extensions and variations to the contract related to both the pipeline relocation and the new signalled intersection at Mirrabei Drive.

Public servants managing the project also told the committee while they knew generally where the gas pipeline was, it was not until work started they realised exactly where it was and that it was initially lain at too shallow a depth.

But the gas network owner, Jemena, has rejected that claim, saying both the original pipe and new pipe were lain between 600mm and 900mm deep, consistent with the relevant Australian standard.

While the government has previously blamed gas network owner Jemena for the delays, the company in turn blamed a third party subcontractor, who the company said damaged pipes while installing the new pipeline, causing further delays to the project.

Transport Canberra and City Services deputy director-general Duncan Edghill said while percentage figures of the delay should be taken with a grain of salt, 75 per cent of the 434 day delay to completing the project were caused by the relocation of the pipeline and a TransACT-owned fibre optic cable.

He said the remainder of the delay was partly due to the government's decision in 2016 to change the Gundaroo Drive-Mirrabei Drive intersection from a roundabout to a traffic light intersection and wet weather.

But city services deputy director-general Jim Corrigan said while the government knew where the utility services were, when they located the gas pipeline, it was not laid deep enough underground, and the pipeline had to be relocated and laid deeper.

Director-general Emma Thomas also said while the government knew where utilities were located, sometimes the data used was not always accurately recorded, while the owners of utilities often did not allow other parties to touch the infrastructure.

Mr Edghill said there was a further issue with utility companies around the country, which were grappling with many infrastructure projects at the same time, affecting the availability of the experts to get on the ground for every project quickly.

"The reality is that we’re somewhat beholden to the timeframe the utility companies take, there's no easy answer to the utilities issue in Australia at the moment, but we hope to minimise the risk and associated potential for delays," he said.

But Mr Edghill said the government was considering changing the way it runs such projects in the future, by having utility works completed prior to the other construction, instead of concurrently as was the case on the Gundaroo Drive project.

Jemena spokesman Michael Pintabona said both the original pipe, and the new one was buried to a depth consistent with Australian standard and it would not have impacted the project timeframe for the road project, but did not clarify whether he was referring to the original pipe, or the new one.