It has been more than a decade in the making and despite time blowouts, a host of near-misses, one collision and the final green light at the 11th hour, Canberra's light rail has finally taken its first passengers.

Key points: Thousands of people expected on first day of service

Thousands of people expected on first day of service Launch comes 16 years after light rail first discussed

Launch comes 16 years after light rail first discussed Project costed at $700 million but came in under budget

The overcast and slightly gloomy start to Saturday was not enough to deter people from getting up early to be some of the first to catch a ride.

The very first at the city station was Jordan Thompson, who said he was excited to be at the front of the inaugural line.

"I wasn't expecting this, I was expecting to be at the back, but I'm really looking forward to it," he said.

"It's going to be good fun, it's going to be a good thing for Canberra and I think a lot of people will enjoy it."

Nick Farrelly said his son Freddy "loves trains" and had been excited to jump aboard.

Nick and Freddy Farrelly were some of the first people to ride Canberra's light rail. ( ABC News: Isaac Nowroozi )

"He told me this morning that he wanted to come down to the train station so here we are, fourth in the queue and looking forward to the trip out to Gungahlin," Mr Farrelly said.

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At Gungahlin, Millie Arandjelovic lined up from 7.30am to secure her spot on the first rides.

"[I'm excited] there'll be no more parking issues, so when you're riding from Gungahlin down to Civic, don't have to worry about parking anymore, so it's just going to be nice and easy," she said.

Some ventured from the opposite end of the city to take part in the historic day.

"I live in Banks so I'm literally the furthest away possible from the light rail," Murray said.

"I've waited for about four years now through the construction and traffic and stuff … this is what I'm most excited for."

Success won't be clear until after holidays

Hundreds of people were expected to ride the light rail on its first day. ( ABC News: Isaac Nowroozi )

Travellers are being offered free trips along the service for the day, with a month's worth of free public transport across both light rail and the revised bus network beginning after the holidays on April 29.

Transport Minister Meegan Fitzharris said the government would be keeping a close eye on how many people used the light rail during that period.

"We're expecting the patronage to start at just under 4,000 in the peak periods and that will continue to build," she said.

"I think we'll have a real sense [of its success] after the first 6 months of operation."

Ms Fitzharris said the Government had capacity to increase the frequency of services along the route if the demand was great enough.

Chief Minister Andrew Barr said he was proud of his Government's achievement, despite a number of sceptics and critics to the plan along the way.

He also said he was aware construction of light rail had taken a toll on some businesses along the route and thanked them and Canberrans for their patience during the process.

"It's very difficult to build an infrastructure project of this scale without some disruption," Mr Barr said.

"I contrast our experience with that that's going on just a few hundred kilometres up the road [in Sydney] where projects are running late, very late, over budget, without any clear sign of a resolution.

"This is the biggest single transport infrastructure project undertaken in the Territory … so it was never going to be disruption-free but it has gone very smoothly."

Light rail was first discussed by the ACT government as a serious consideration around 16 years ago, but the idea has been around much longer than that.

Canberra's designers, Walter Burley Griffin and his wife Marion, envisaged a tram network for the city more than 100 years ago and the idea has been debated since then.

While the cost of the service was originally announced as $707 million for the first stage from Gungahlin to the City, Ms Fitzharris recently said the project came in under budget and full details would be released in the coming weeks.