In March, the government signed a $107,181.45 contract with Kicks Entertainment to coordinate the launch event on a Saturday.

The contract required Kicks Entertainment to manage queues and co-ordinate traffic and crowd management around the light rail stops.

An ACT government spokeswoman described the event as a "thank you to the Canberra community".

But the total launch event cost $446,000, government officials revealed during ACT estimates on Friday.

That included $292,000 for traffic management and security along the route and at events, and $154,000 for entertainment.

Transport Canberra's Ed O'Daly said the traffic management and security was essential for safety on the day, due to the public interest in the launch.

"On top of that there was a modest celebratory event that we did at the same time," he said.

Opposition transport spokeswoman Candice Burch said it was staggering to learn almost half a million dollars of taxpayers' money was spent on the party.

"I think many Canberrans would be shocked at this unnecessary expense," Miss Burch said.

"This is another example of how the government is so reckless with ratepayers' money.

"Let's not forget the thousands of Canberrans who are living in poverty, or the thousands of Canberrans, including children, who have had their bus taken away from them because the government says they don't need it."