What does Sydney's train strike mean for the city and commuters?

The scale of the disruption Sydney's looming strike action and shutdown of city's trains this weekend is becoming clearer.

The Rail, Tram and Bus Union (RTBU) industrial action will now begin from Friday morning and it means train services across Sydney, as well as any inter-city services, will halt for more than two days.

Those services are expected to recommence from mid-morning on Sunday. 

"This will cause significant disruption to people's lives and to the operation of our city," NSW Minister for Transport Jo Haylen said.

"You can't simply click your fingers and change the way a very big system works."

What does the planned train shutdown mean for Sydneysiders? (702 ABC Sydney: Amanda Hoh)

Are any trains running this weekend?

The vast majority of trains are expected to stop running during this industrial action period from Friday morning onwards.

The union had initially said the strike would begin from Thursday 10pm, but they have since agreed to run normal services on Thursday, including the planned 86 additional services to Olympic Park for a Pearl Jam Concert.

NSW Transport secretary Josh Murray said that alternative services, including replacement buses, ferries and rideshare services, are being explored to lessen the shutdown's impact.

"However, they will already be running on Thursday and Friday at their usual capacities, and so the amount of extra capability on the bus and ferry network will be tested," he said.

City services will be affected by the shutdown. (ABC News: Blair Chapman)

There is also track work on the Metro this weekend and some replacement buses will be running. 

Senior lecturer in transport management at the University of Sydney, Geoffrey Clifton, said despite replacement transport plans, it's likely the impact will still be felt by commuters.

"There's just not spare capacity lying around idle to replace the trains."

Why are Sydney trains striking?

The shutdown is due to a deadlock between the RTBU and NSW government, with months-long negotiations over a new enterprise agreement for workers continuing.

The government said it could not agree to the union's demand for 24-hour train services like it did last weekend.

"We've seen the transport minister come out three times in the last 24 hours, which is more times than the NSW government has negotiated with us," RTBU NSW secretary Toby Warnes said.

"All we're doing is calling on the government to come back to the negotiating table and get this deal done."

Services are expected to recommence from Sunday morning. (AAP: Dan Himbrechts )

When will the Sydney trains strike end?

This shutdown will repeat every week until a resolution is reached, a Transport for NSW spokesperson said.

It presents a dilemma for those reliant on public transport.

Roughly 720,000 passenger journeys occur each day via Sydney's train network, according to government figures.

"Trains are vital to getting Sydneysiders around and we just don't have anything which can replace them," Dr Clifton said.

"There's going to be massive disruption."

Dr Clifton said Sydney's train network is vital for the city. (AAP: Nikki Short)

Congestion expected

An influx of traffic congestion across Greater Sydney is anticipated too.

"Even if they get more buses out on the streets, they'll be stuck in traffic congestion, which means the buses are going to be running slower and people won't be able to rely on a bus to get them to work, even if there is a bus available," Dr Clifton said.

The shutdown will result in more traffic congestion, Dr Clifton predicted. ( ABC News: Keana Naughton )

But the increased demand could also spark greater availability of rideshare services, like Uber, over the period, albeit to higher prices.

"Surge pricing is obviously a concern for travellers, but it's a key mechanism for getting more drivers out onto the streets," he said.

"It's a question of, 'Will people be willing to pay the higher prices in order to secure the ride?'"

According to a spokesperson for the Australian Competition and Consumer Commission (ACCC), it is not illegal in Australia to increase prices due to high demand, but any surge or dynamic pricing must be made aware up-front.

Concerns for essential services

A second, potentially dire, side effect of the shutdown could be reduced access to essential services, including emergency healthcare.

"We would have to expect that there will be some essential workers who just won't be able to get to their jobs because of the lack of trains," said Dr Clifton.

Increased traffic congestion could lead to reduced access for emergency services, Professor Clifton said. (ABC News: Keana Naughton)

The extra buses and cars on the roads will also likely create congestion, which could slow down essential services driving to emergencies.

"I wouldn't want to be waiting for an ambulance during this time, particularly for [anyone] living in the congested parts of Sydney."