Sydney's 20-somethings are fast ditching their cars for public transport, previously unpublished figures show, revealing the trend is widespread in the city.

An analysis of new travel figures from the Bureau of Transport Statistics shows the generational shift to public transport is not confined to well-serviced inner areas but also in outer Sydney, where public transport is more patchy.

The transformation in travel patterns, experts and surveys say, is likely caused by the cost and inconvenience of maintaining a car but also the widespread use of mobile devices, which are more attractive on public transport.

Ten years ago, people aged 21 to 30 in Sydney drove themselves on about 53 per cent of all trips on an average weekday. That share fell almost eight percentage points to 45.5 per cent in 2011-12.

Among people aged 31 to 40, the ''mode share'' of driving trips fell from 64.2 per cent to 60.2 per cent in the decade. Sydney residents in their 40s and 50s are also driving less but the trend is not as pronounced and residents in their 60s and 70s are, on average, driving slightly more.