Deanna "Violet" Maree Coco was sentenced in the Downing Centre Local Court on Friday for a protest conducted in April as part of a Fireproof Australia movement.

The 22-year-old protester was part of a two-car convoy which disrupted peak-hour traffic at about 8.30am on April 13 to raise awareness of climate change.

She was sentenced to a non-parole period of eight months, expiring on July 31, 2023, for breaching traffic laws by blocking traffic, possessing an orange flare in a public place, and resisting police after being asked to move on.

Her full prison sentence stretches to February 31, 2024.

Coco was fined $2500 for using the flare while on top of a pantech truck parked on the Harbour Bridge.

The protest disrupted traffic and prevented an ambulance with lights and sirens blazing from reaching an emergency, police said.

Officers alleged that she and Alan Russell Glover were in the truck while Jay Larbalestier and Karen Fitz-Gibbon were in the second vehicle, a Kia.

"Fitz-Gibbon and Larbalestier got out of the Kia and sat in front of the white Hino truck with a red and white 'Fireproof Australia' banner. Fitz-Gibbon and Larbalestier also glued one hand each to the roadway," police wrote.

"The accused and Glover got out of the truck and climbed onto its roof. The accused and Glover both lit flares whilst atop the truck."

The protest, which was live-streamed on social media, used significant police resources, the court was told.

Coco's lawyer Mark Davis told AAP he was disappointed with the sentence and had already challenged it on appeal.

"We are extremely disappointed in this outcome. This is the first person to be imprisoned under the new Roads Act amendment .... which is essentially being properly seen as an anti-protest law," he said.

The amendments, which passed NSW Parliament in April, created new offences for activities which disrupted or damaged major roads or public facilities.

Mr Davis said Coco's crime was at the lower end of seriousness, saying she had only blocked one of five lanes on the bridge.

"She's a very committed, very gentle young woman, with no violence in her past, no damage to property. She's a sincere person and it's distressing to us that she's now in prison," he said.

An appeal of the sentence will be heard in the District Court on March 2. Mr Davis said he would make another bail application in that court after attempts to secure Coco's freedom were rejected by the Local Court.

Sophie McNeill of Human Rights Watch slammed the court's "outrageous decision" on Twitter.

Human Rights Watch previously examined Coco's case in May, she wrote.

"We found climate protesters like her were being increasingly and disproportionately subjected to vindictive legal action by Australian authorities that is restricting the rights to freedom of peaceful assembly and expression."

Australian Associated Press