Public transport in Sydney's west is shaping up as a key battleground in the state election campaign after Labor leader Michael Daley vowed to spend $8 billion to "fast-track" a new metro train line between Parramatta and the central city.

In a pitch designed to resonate with voters in vulnerable seats in the city's west, Mr Daley said the funding injection meant Labor would deliver the signature rail project – the total cost of which has been estimated at up to $18 billion – "more quickly" than the Berejiklian government.

A driver who rammed into a railway signal box delaying services has reignited the political posturing over Sydney's ageing train network. The opposition has promised to spend big to speed up construction of a metro link between the city and Parramatt

The bulk of the money Labor has committed to the new rail line, if it wins the election on March 23, would come from cancelling toll road projects such as the Beaches Link in the city's blue-ribbon north-east.

Mr Daley would not say how the new Sydney Metro West rail line would be fast tracked, or how much earlier it would be completed, sparking accusations from the government that he was making "empty promises" to voters in the city's west.

Instead, he said a Labor government would "at least match" the Coalition government's promise to have the line open by the late 2020s.

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"Our hope is that we will get it done more quickly," Mr Daley said. "These projects can be delivered much more quickly if you have a big upfront injection."

The $8 billion includes $3 billion already committed to the project by federal Opposition Leader Bill Shorten, should Labor win government at the federal election.

State Labor has said it will cancel the proposed $14 billion Western Harbour Tunnel and Beaches Link toll road project, as well as a conversion of the existing Sydenham-to-Bankstown rail line to carry metro trains, and direct the money needed for them to Sydney Metro West.

It has also vowed to ditch an extension of the F6 motorway in Sydney's south, the first stage of which has been estimated at up to $2.6 billion. Funds for the F6 would form part of a $3 billion package Mr Daley unveiled on Monday for the existing rail network.

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The Berejiklian government will sharpen its campaign pitch on public transport in the next few weeks when it releases more detail about Sydney Metro West. That will include the likely timing of construction, and the final number of train stations and their locations.

Transport Minister Andrew Constance stepped up his attacks on Mr Daley for promising to cancel vital projects in Sydney such as the Western Harbour Tunnel, and ridiculed his ability to fast-track construction of a metro train line between Parramatta and the CBD.

"He’s got no start date, no end date – how can you fast track a project without a date?" he said.

"He can’t on one hand say he needs all planning approvals and a parliamentary inquiry before he starts the job, and then tell everyone he is going to fast-track it. We have a record of fast-tracking these projects – Labor has a record of cancelling these projects."

But Mr Daley said his policies were "modest, real, affordable, costed and focused on people".

They include allowing local communities and the business community to view plans for transport projects worth more than $1 billion through "public planning inquiries".

When it first announced the Metro West project in late 2016, the Coalition government said it wanted construction of the line for single-deck trains to start within five years – or by 2021 – and for the line to open in the second half of the 2020s.

Mr Constance last month vowed that project's construction would be "well under way" in the next term of government if the Coalition was re-elected.

It earmarked $3 billion for the Metro West in last year's state budget.

Leaked documents have shown that Transport for NSW estimates the project will cost up to $18 billion. However, the final cost will depend on the route chosen and the number of stations built.

Mr Daley said the $3 billion package for Sydney's existing rail network would be guided by a board of experts to increase services and improve reliability.

"Trains are running late, the system can't cope with increased demand and the public can no longer rely on government to deliver to deliver a basic service," he said.

Mr Daley's rail commitments were accompanied by a number of other transport announcements, including a promise to spend $900 million improving regional and rural roads, and a further $1.1 billion expanding the government's $825 million pinch-point program, which aims to ease congestion on Sydney's major roads.

He also promised to give $10 million to Liverpool council to undertake a feasibility study and prepare a business case for a rapid transport system between Western Sydney Airport and the city's south-west.