From the outside they look a lot like any other train, but if you peer in the window there is a big difference — fewer seats and no driver.

Key points: Sydney's new Metro trains are being tested at Rouse Hill

Sydney's new Metro trains are being tested at Rouse Hill They have less seats, but much more standing room than their double-decker counterparts

They have less seats, but much more standing room than their double-decker counterparts The driverless trains will run every four minutes during peak periods

By next year, Sydney's new driverless trains will be ferrying tens of thousands of passengers on the Northwest Metro line between Rouse Hill and Chatswood.

The first three trains are being tested on tracks at Rouse Hill, and were today unveiled by the New South Wales Government.

Premier Gladys Berejiklian inspected the new trains this morning and said it was a thrill to see how the project was progressing.

"To actually have the opportunity to walk on this future train, to see what customers will be experiencing on the new rail line is actually really uplifting, because we've never had a service like this before in Australia," Ms Berejiklian said.

The new metro trains will run every four minutes in peak periods, before the line is eventually extended under the Harbour to the CBD and, eventually, to Bankstown by 2024.

Less seats but more room

The carbon steel and stainless steel trains are 132 metres long and weigh 240 tonnes.

Inside the single-deck trains there are fewer seats and much more standing room than a traditional Sydney double-deck train.

It means some passengers may need to stand for up to 40 minutes for the journey from Rouse Hill to Chatswood.

The testing is being conducted at Rouse Hill. ( Supplied: NSW Government )

The Premier defended the decision to have fewer seats, arguing it increased capacity and would cut travel times by making it faster for people to get on and off at each station.

"There are sufficient seats for everyone who needs one," Ms Berejiklian said.

"Some people will be going all the way to the final destination but others will be hopping on and off during the journey."

Meanwhile, thousands of commuters who catch the existing double-decker trains from Macquarie Park to Chatswood are preparing for the line to be shut down for up to seven months later this year to allow conversion of the tracks to handle the new metro.

Ms Berejiklian said the inconvenience would be worth it.