The Baird government's $2 billion CBD light rail project has come under criticism in recent weeks. NSW's former Liberal premier and infrastructure boss Nick Greiner has argued it will compound congestion already clogging Sydney's spine.

Labor's transport spokesman Ryan Park argues trams will overwhelm the CBD's narrow streets and particularly its intersections. The Action for Public Transport lobby group has estimated that the government's modelling of light rail routes would require interruptions at traffic lights from Circular Quay to the eastern suburbs as frequently as 60 times per hour.

But transport experts have made the argument that light rail has the potential to speed up the flow of traffic.

Greg Sutherland, a tram expert and former government transport adviser, argues that a new tram fleet would take about 15 seconds to cross George Street intersections.

"Trams will be through intersections faster than a current Sydney diesel bus," he said. "And the [breaks] available for cross traffic will increase."

Mr Sutherland argues because they can carry five times as many passengers as buses, trams will cut down on chains of slow-moving peak-hour traffic.

Dr Michelle Zeibots from the University of Technology Sydney says the effects of the light rail on traffic will depend on whether the state government reprograms Sydney's traffic lights to fit trams.

She points to cities such as Zurich which in the 1980s re-engineered traffic light systems to accommodate tram networks. There trams are given priority but cars are a given green light before a tram has passed an intersection, which, Dr Zeibots says, primes drivers to move as soon as trams have cleared and cuts down on "dead time" when intersections are empty.

Transport Minister Andrew Constance said the government is reviewing traffic signalling as part of the project.

But how CBD traffic flows look once the light rail is completed in 2019 hangs perhaps most of all on whether more or fewer cars continue to travel through the city.

On balance,Sutherland argues the light rail will move vastly more people through the city quickly, but at first its impact on the overall flow of traffic will be neutral.

He says if cars continue to pour onto the road to take up the spaces vacated by buses, those benefits will be reversed.

Dr Zeibots says international research shows that when you remove cars from a section of a city as the government plans to do with about half of George Street, fewer people see driving through the city as convenient.

"With new motorways we get … traffic growth," she said. "Pedestrianise half of George Street and we'll get ... reductions."

Similar projects around the world, she says, have reduced the number of cars on the road by between 20 to 60 per cent.

Four questions the government must answer

1. Where are the buses going to go?

The light rail will require hundreds of buses to be re-routed through the city. The government is yet to reveal exactly how the city's other major road arteries – such as Elizabeth, Castlereagh, Park and Druitt streets – will pick up the slack. In announcing details about the line's construction last month, Transport Minister Andrew Constance said the movement of some stops will "typically mean walking to an adjacent city street for a new service". More detail is expected when the new bus timetable is released in October. "Customers will be given plenty of time to familiarise themselves with the new timetable before it is implemented," Mr Constance said.

2. Will the line really have the capacity to carry everyone who wants to use it?

It has been estimated that the line will move up to 13,500 people every hour, or "up to 450 people" per vehicle – the same number of commuters carried by nine standard buses. But groups like community action group Fix NSW Transport argue the real capacity would be far less and would not meet demand during peak periods. For instance, the group's spokesman Jim Donovan said each of the 67-metre trams, which were previously said to have a capacity of 466 people, would more realistically carry about 400 people. "Only 120 [people] will have seats," Mr Donovan said.

3. Will businesses along the route be compensated?

Work on the light rail will be staggered across 31 construction zones over the next three years once work begins in October, with each zone expected to be in place for between eight and 13 months. The state government will offer businesses facing major disruptions access to support including workshops, and promised help to minimise the impact on deliveries and servicing. But it has not yet said whether or not any will be financially compensated. "The NSW Government is continuing to work with the business community on further assistance measures," Mr Constance said.

4. How would the line be extended in the future?

If the Circular Quay to eastern suburbs light rail is deemed a success, would the network be extended – and where to? The City of Sydney wants a light rail connection between Central and Green Square. Randwick Council pushed for the line to be extended through to Maroubra Junction. And what about Parramatta Road?

– with Leesha McKenny