Detailed plans for a light rail line along Parramatta Road linking Sydney's central business district to Burwood were developed by the state's transport agency, but were abandoned several months ago.

Fairfax Media has obtained extensive planning documents for a Parramatta Road light rail line, developed last year and early this year for Transport for NSW.

The project, estimated to cost up to $2.7 billion, would aim to take advantage of the WestConnex motorway to be completed in 2023.

The light rail line would include about 15 stops on Parramatta Road, and the route would run between Burwood Station and a terminus near Museum Station.

The line would provide a more reliable and efficient service than the bus network, which on Transport for NSW's own analysis suffers from a lack of capacity and poor customer satisfaction.

Despite the extensive plans, it is understood Transport for NSW scrapped work on the scheme in the first three months of this year.

The department also said the plans obtained by Fairfax Media, which included hundreds of pages of costings, assumptions and block-by-block designs as well as multiple documents marked "cabinet in confidence", were "never considered by government."

According to a "cabinet in confidence" document dated November 2016, the light rail line would have delivered multiple benefits for Sydney's inner west.

The tram trip from Burwood to the city was estimated to take about 22 minutes, compared with a 39-minute bus journey along the same route.

Early planning for the project assumed a tram running every four minutes in peak periods. There would be an overall improvement in traffic conditions as more commuters shifted to the light rail line. Traffic at some intersections, however, would worsen, particularly around City Road and Broadway.

With an extra 220,000 people expected to live along the Parramatta Road corridor in the next 15 years, the Transport for NSW studies depicted the light rail project as helping to take pressure off the over-loaded transport network.

The inner west heavy rail line, the bus network, plus the existing inner west light rail line, are "unable to accommodate already projected growth", a document prepared for a "risk workshop" says.

This document notes that bus satisfaction levels in the inner west are the lowest in Sydney, and bus speeds significantly below best practice in the city. The Transport Minister Andrew Constance this year used these facts as a reason to privatise the operation of bus services in the area.

The documents obtained by Fairfax Media also depict the light rail project as crucial for taking advantage of the WestConnex motorway, which will open in stages leading up to 2023.

WestConnex will provide an opportunity to improve the "urban form" of Parramatta Road, "subject to other initiatives taking timely advantage of this opportunity".

When the M4 East section of WestConnex was approved last year, then planning minister Rob Stokes imposed a condition that two lanes of Parramatta Road be reserved for public transport, unless a better public transport initiative was supplied.

The light rail line would satisfy those conditions. It is unclear how the government plans to satisfy those conditions if it does not build the tram line. It had said it would build a metro rail line between Parramatta and the city, but has committed only to intermediate stops at the Bays Precinct at Rozelle and at Sydney Olympic Park.

Mr Constance is on leave. A spokesman for Transport for NSW said the department regularly looked at transport options to consider their potential.

"Only very early assessments of this potential approach were carried out and it has never been considered by government," the spokesman said.

"Transport for NSW is still investigating public transport options to be implemented following the opening of WestConnex to support urban renewal and revitalisation of Parramatta Road.

"Such plans will also complement initiatives to improve customer services, including Sydney Metro West, which is currently in a consultation phase."

The spokesman said the decision to franchise inner west bus services was not linked to the future planning of Parramatta Road transport.

It is understood the project director of the Parramatta Road light rail scheme quit Transport for NSW after work was scrapped this year.

Construction of the project was timed to work around WestConnex. Construction work off Parramatta Road, for instance on a stabling yard, and in Burwood, would have happened before the completion of the motorway in 2023. Once the motorway was finished, the Parramatta Road work would start, allowing the tram line to open in 2025.

A separate light rail project from George Street to the eastern suburbs should open in 2019. Construction of a tram line from Westmead through Parramatta to Carlingford should start next year.