The NSW government has denied it builds multi-billion dollar road projects using half-century-old traffic modelling techniques.
The NSW government has hit out at an academic's claim that flawed, half-century-old traffic modelling techniques are being used to justify multi-billion dollar road projects.
The traffic modelling used by the state government to justify travel time benefits for projects, including the $16 billion WestConnex, was designed in the 1950s, Professor Michiel Bliemer says.
"Usually the travel times are underestimated," Dr Bliemer told AAP on Monday.
The University of Sydney academic and Transport Network Modelling chair said the current modelling is based on the same assumptions that were made 60 years ago when there was almost no congestion.
"The formula accepts all the traffic on the roads - it just doesn't stop it. That's the problem. They just let everything flow through to their destination," he said.
"They should be held up in queues and that doesn't happen in the old model. They just go through without any impediment."
Dr Bliemer said the government was aware the modelling techniques produced "unrealistic assumptions" of traffic flow.
But the Roads and Maritime Service says their models - including those used on WestConnex - are modern and backed by expert opinion.
"The modelling is the most modern, tried and tested currently used by industry and did not exist in the 1950s," a spokesman told AAP in a statement.
"The complexity and computational power simply did not exist until recently."
The spokesman said any assertion the RMS was using outdated or flawed models was "incorrect".
Dr Bleimer argues NSW is not alone with many other governments using dated techniques.
He argues the government could receive inaccurate travel time benefit data, which it uses, in part, to justify embarking on expensive road projects.
"You may be building infrastructure maybe not in the right location," he said.
Dr Bleimer claims he's developed a mathematical model which could cope with the size and complexity of Sydney's roads and is already being used in the Netherlands.
RMS says it uses a number of modelling techniques that simulate traffic movement based on vehicle flow, lane changing and gap acceptance - among other variables.
The spokesman on Monday said the government was happy to brief Dr Bleimer so he can "better understand" its approach.