Australian millennials are taking longer to get their licence, relying on public transport instead, according to a global study.

The study, led by researchers from Victoria's Monash University, compared the travel behaviour of young adults in cities including Melbourne, Brisbane, Atlanta, London and New York.

All cities, apart from New York, recorded an increase in kilometres travelled by millennials on public transport in the past 10 to 15 years, with Brisbane the highest at 66 per cent and Melbourne by 45 per cent.

While car travel by young adults in Brisbane also increased over the same period by 16 per cent, kilometres travelled by car in Melbourne was almost the same as it was in the early 1990s.

Researchers say this may reflect the steady decrease in young Victorians getting a driver's licence, from 76 per cent in 2000 to 57 per cent in 2018.

"At this rate, only half of 18 to 23-year-olds in Melbourne will get a licence by 2025," report lead researcher Alexa Delbosc from Monash said.

The increase in public transport use in Melbourne was greatest among low-income earners and parents of young children, in part due to the investment in new, high-frequency bus services since the 1990s.

"We also saw big increases in train patronage, reflecting strong growth in jobs and housing in the city centre," Dr Delbosc said.

Meanwhile, Brisbane's public transport supply increased more than any other city in the study, with a 40 per cent increase in service kilometres since the early 2000s when the city rolled out its new bus network.