Los Angeles traffic congestion presented the perfect opportunity for Hollywood star Renee Zellweger to practice hitting the high notes for her latest film role.

The Oscar-winning actress stars as the ageing Judy Garland in her new film and performs the songs herself but it took a year to get her voice up to scratch.

“It would have been a struggle for anyone having to listen to me hit those notes but I did that mostly in the car, stuck in traffic,” Zellweger told AAP on Tuesday from the red carpet Australian premiere in Melbourne.

“I finally found something that LA traffic is good for.”

The role piqued her interest after she was invited to England to discuss the script.

“I just became greedier and greedier for information,” she said.

“We just started trying things and then one thing led to the next and we never actually made the declaration ‘now we’re going to do this’, it just sort of took over.”

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Zellweger is well known for her role in Bridget Jones’ Diary and won an Oscar for her performance in Cold Mountain.

Wearing an off-the-shoulder black gown and pointed stilettos the 50-year-old stunned the crowd and posed for selfies with fans who braved chilly weather to attend.

Zellweger‘s performance as Garland has already been praised by critics, with the actress’ singing voice on show again after making a debut in the 2002 film Chicago.

Judy follows Garland’s life in 1968, three decades after she shot to stardom in The Wizard Of Oz.

It shows Garland as she prepares for a series of sold-out shows in London and her personal and professional challenges.

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Watch Jonesy & Amanda’s interview with the Academy Award winning actress above!